Welcome to Module 11!

Living on Earth I: Evolution & Extinction

White Ford Mustang Convertible

Credit: 1964 mustang by DougW at English Wikipedia, Public domain, via Wikipedia

Ah, memory lane. Dr. Alley's best friend in early elementary school had a father who sold "pop" (also called soda, or soft drinks) to dealers in Ohio and often had free samples sitting around, and a mother who drove a 1964-and-a-half white Ford Mustang with a black convertible top. Hard to beat. And what a beauty that car was! Dr. Alley's Hot Wheels Mustang was a 1967, recognizably different from the '64-and-a-half. In fact, he could easily put the Mustangs in chronological order based on the differences between models.

The early geologists of the late 1600s and 1700s had never heard of Ford Mustangs, but those geologists faced a Ford Mustang problem. Recognition of unconformities and other features in the rock record opened a world far older than written records. William Smith had demonstrated the usefulness of the law of faunal succession, so those geologists knew that putting the rocks in order put the fossils in order, and thus the biological change had accompanied geological change. But was the biological change gradual, parent to child in a great, unbroken evolutionary chain of being? Or did unknown cataclysms, or a tinkering god, or an angry god, repeatedly replace one world with another as Ford would one day replace each Mustang with a new model the next year?

Erasmus Darwin was a doctor with an interest in nature, and he put his ideas about evolution into poetry, which was published after he died. A few of his lines from The Temple of Nature (1802):

Organic life beneath the shoreless waves
Was born and nurs'd in ocean's pearly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;

These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing.

Source: University of California Paleontology Museum

OK, maybe this excerpt wouldn't make a hit song if put to music. But when his grandson Charles Darwin added observations and understanding of mechanisms of evolution to Erasmus' speculations, the evolutionists won the scientific argument over the Ford-Mustang "catastrophists." What convinced the scientific community (and "polite society") that evolution is indeed correct? We'll try to answer that fascinating question in this lesson.

Learning Objectives

• Understand that evolution is fact and more, predicts as well as explains, helps people do useful things, is not anti-religious, and that there are no serious competing scientific ideas.
• Explain how diversity generated during the reproduction of living things affects the ability to survive and reproduce, with successful experiments being passed on to accumulate and drive evolution.
• Describe how natural climate changes, and in one case a meteorite impact, have led to rapid mass extinctions that opened up opportunities for the slow evolution of new types.

What to do for Module 11?

You will have one week to complete Module 11. See the course calendar in Canvas for specific due dates.

• Take the RockOn Quiz
• Take the StudentSpeak #12 Survey
• Continue working on Exercise #6

Questions?

If you have any questions, send an email via Canvas, to ALL the Teachers and TAs. To do this, add each teacher individually in the “To” line of your email. By adding all the teachers, the TAs will be included. Failure to email ALL the teachers may result in a delayed or missed response. For detailed directions on how to do this, see How to send an email in GEOSC 10 in the Important Information module.

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Main Topics: Module 11

Evolutionary Theory includes Facts and Much More

• A scientific theory is an explanation of nature that has been tested and confirmed repeatedly, that predicts successfully, and that places facts and laws into a larger context to help us understand and make new predictions.
• The theory of evolution is highly reliable and useful, not tentative and uncertain.

Easy Come, Easy Go--How Evolution Works

• Parents reproduce by having kids.
• Kids include experiments introduced during reproduction—the kids are not identical to their parents.
• These differences often affect the ability of the kids to survive to have their own kids. This leads to natural selection - the kids with differences that favor survival tend to survive to have kids.
• But, despite the differences, kids are quite similar to their parents—the kids just receive a bit more or less of what makes their parents biologically successful.
• These processes acting over time give evolution—successful experiments accumulate in new generations, and unsuccessful ones are eliminated so that new generations slowly become different from older ones.
• Changes to living organisms are not passed on (if you get a tattoo, your kids will not be born with tattoos)—but the reproductive experiments are passed on.
• Major changes must occur slowly over many generations, often thousands or more, to maintain “back-compatibility” — everything in a living organism needs to work together, so huge jumps do not succeed.
• Thousands of generations or more require a lot of time for large animals but can occur in less than a year for disease organisms.

The Unbroken Chain

• The Law of Faunal Succession that we met in Module 9 suggests that evolution has occurred.
• Evolution predicts gradual changes over time, and thus the occurrence of transitional forms, whereas other hypotheses such as special creation or catastrophism predict that there will not be transitions.
• Transitional forms have been found, strongly supporting evolution:
  • Transitional forms are common in commonly fossilized types.
  • And less common in less-commonly-fossilized types.
  • Transitional forms are found as often as evolution predicts, and the fossil record disproves competing hypotheses.
  • Transitional forms are not found everywhere for every species in the fossil record, in part because new species often evolved geologically rapidly from small populations in isolated places (it is easier for a smaller group to evolve).

Taking Care of Business

• The theory of evolution is explanatory, predictive, and useful.
• Germs are evolving antibiotic resistance, and the scientists trying to keep us alive are using knowledge of evolution to fight those germs.
• Computer scientists mimic evolution to solve complex problems (evolutionary computing).

Teach the Conflict?

• Scientifically, there is no conflict to teach—there is much to learn and do, but with no serious problems or competitors to our understanding of evolution.
• In particular, evolution is:
  • Consistent with the second law of thermodynamics, and all other known physical laws,
  • Strongly supported by the fossil record and age dating,
  • Not anti-religion (indeed, it is supported by many religious groups).
• There is widespread and very strong scientific consensus that so-called competitors (e.g., “intelligent design”) are not science.
• Thus, “teaching the conflict” would require teaching non-science in science classes (but note that some groups, at some times, have tried to do just that).

Extinction Can Ruin Your Whole Day

• There has been a slow "background" rate of extinction, with species being lost about as often as new species appeared during most of geologic history (populations fluctuate up and down and sometimes hit zero, which is extinction).
• Occasionally there were mass extinctions when species became extinct much more rapidly than new species arose, but these mass extinctions were followed by millions of years when new species arose slightly more rapidly than old species became extinct, thus restoring biodiversity over millions of years.
• Major extinctions included:
  • the end-Paleozoic mass extinction: volcanic CO₂ drove extreme global warming.
  • the end-Mesozoic mass extinction: a meteorite triggered immense changes in climate
  • a few others that we won't make you learn in detail, that mostly were caused by large volcanic releases of CO₂ that drove heating, loss of oxygen in the ocean, and other changes (note that the modern CO₂ rise is unequivocally from humans, not from volcanoes, as we will see in Module 12).
• The dinosaurs were doing just fine until killed by changes triggered by a meteorite impact (and, some dinosaurs that were ancestors of modern birds did survive).
• The death of all of the non-bird dinosaurs freed ecological jobs (“niches”), allowing evolution to produce large mammals over the 65 million years between the meteorite and us.

The Dinosaur Killing Meteorite of 65 Million Years Ago

• Evidence: the geologic record of the extinction event occurs with an odd sedimentary layer containing much iridium (common in meteorites, otherwise rare on Earth), soot from wildfires, high-pressure shocked quartz, droplets of melted and then rapidly frozen rocks, a giant-wave deposit in places near the Yucatan including the Caribbean, and a giant crater of the right age on the Yucatan Peninsula.
• Mechanisms: the meteorite blasted things up, causing a fire from the heat when those things fell back to Earth, then cold and dark, from the sun-blocking effect of slow-falling things that also had been blasted up, with acid rain and then heating from CO₂ released from the sulfate and carbonate rocks where the meteorite hit.
• A thought: there still are big rocks out there in space—averaged over millions of years (and presuming we humans hang around that long), they are likely to kill as many people as commercial airline crashes, but not nearly so many as car crashes, and we can reduce the dangers from airline crashes and car crashes.

Evolution on a Plate

Start by watching this one-minute-and-fifty-five-second video showing the evolution of antibiotic resistance. The medicines that saved the lives of your grandparents from nasty diseases often are completely useless for you, because the disease organisms have evolved. As explained in the video, the researchers prepared a simple demonstration of this important process. They started bacteria growing in good food for bacteria, but with nearby bands of this food containing low and then higher concentrations of an antibiotic. The bacteria initially grew rapidly in the food without antibiotic, but as the bacteria spread, they encountered a low concentration of antibiotic. You will see the growth of the bacteria stop as the antibiotic killed them… until first one and then another cell evolved a defense against the antibiotic, allowing the offspring of those special new bacteria to grow rapidly into the antibiotic-bearing food. The process repeated as the bacteria encountered higher and still higher concentrations of antibiotic. In 11 days, the bacteria were rapidly growing in the highest concentration of antibiotic, and were essentially immune to that medicine. (The researchers did destroy these bacteria after the experiment, but dealing with similar processes involving bacteria, antibiotics, and people is a very important issue.)

The evolutionary changes shown in this video were very small, although obviously important. But, the time used in the experiment was a tiny, tiny fraction of the billions of years of life on Earth. Evolution is real, and knowledge of it is really useful. So, let’s go visit a fascinating National Monument, and get started on evolution.

Video: The Evolution of Bacteria on a “Mega-Plate” Petri Dish (Kishony Lab) (1:55 minutes)

Evolution and the Florissant Fossil Beds

Florissant Fossil Beds Location

Credit: R. B. Alley © Penn State
is licensed under CC BY-NC-SA 4.0

In south-central Colorado, at Florissant Fossil Beds National Monument, you can visit a unique deposit of fossil trees, leaves, insects, birds, fish, and more from about 35 million years ago. At that time, a lava flow dammed a stream to form a lake. Then, repeated volcanic eruptions dropped silica-rich ash into the lake, making the water silica-rich and favoring the growth of diatoms, single-celled algae that have silica shells. When a leaf or dead bug fell into the lake, huge numbers of diatoms quickly grew on it in very thin layers, protecting it from decay until it was buried by paper-thin layers of ash and mud. Like flowers pressed in a phone book, the flowers of that ancient time can still be seen clearly. So can the dragonflies, bees, and mosquitoes.

There are, however, certain differences between some of those creatures and similar ones that live today. Remember, back at Arches National Park in Module 9, we learned about the law of faunal succession—when rocks are placed in order from oldest to youngest, the types of fossils in the rocks also fall into order, becoming more like things alive today in younger and younger rocks. The Florissant rocks are relatively young, and their fossils are immediately familiar to modern people, but the fossils are not identical to modern species.

Petrified sequoia tree stump, Florissant Fossil Beds National Monument, Colorado.

Credit: R. B. Alley © Penn State is licensed under CC BY-NC-SA 4.0

The law of faunal succession suggests the possibility of evolution but does not prove it by any means. One early theory held that many creations and extinctions occurred over geologic history, something like the history of automobiles. One type of automobile does not give birth to another; new ones are created. But you can place the automobiles in order from oldest to youngest, and the younger they are, the more they look like modern automobiles. This idea was called catastrophism in geology. The fundamentalist interpretation of biblical creation is a one-event form of catastrophism.

Virtual Field Trip: Florissant Fossil Beds National Monument—Gnattily Dressed

Evidence of Evolution

Catastrophism eventually lost out scientifically to evolution, because evolution succeeds but catastrophism fails to explain the patterns of fossils and of living things, and to predict events such as the emergence of antibiotic-resistant microorganisms. The triumph of evolution over catastrophism owes much to biology, and more recently to genetics and molecular biology; the identification of the mechanisms driving evolution was especially important (see below).

As geologists collected more data, they joined the biologists in recognizing that evolution explained the data and predicted the next discoveries better than any catastrophist model, or any other model that anyone had ever suggested. The early geologists could see the clear change of types over time but saw catastrophic elements in the record as well. In many places, geologists would find fossils of one type, and then of a somewhat different type, with no transitions between them. Evolution implies rather gradual change, not big jumps. The early geologists knew, however, that there were big time jumps in the records (remember the many unconformities—time gaps—in the Grand Canyon sequence). So some of the jumps in the fossil record were related to the incompleteness of the rock record. And, there really were catastrophic extinction events in the record such as the meteorite that killed the dinosaurs (again, see below).

Further study has shown that many of the evolutionary changes have been biologically slow but geologically fast - recall how long geological time really is! And, many of the evolutionary changes occurred in small isolated populations that are not likely to have been fossilized. Suppose that a few animals of some type colonized a small island. Then, they had babies who had babies who had babies, a generation per year, thousands of generations in a geological eyeblink. If the babies differed by just a tiny bit from the parents, eventually a new type or species would have emerged. If that species then succeeded in escaping the island (say, because sea-level fell and the island became connected to the mainland), a new type could appear suddenly on a nearby continent. Sediments from the small island may have been subducted or otherwise destroyed, but fossils on the larger continent are more likely to have been preserved. A small island may support only a few individuals, so there never would have been many critters to produce fossils that humans could find. On the continent, the species might flourish and produce millions of individuals that left easily collected fossils. Thus, the fossil record would show a sudden jump when the actual process was gradual.

The eye of a Phacops trilobite, composed of individual elements in columns.

Credit: NASA

In one famous case (of many), trilobites of the genus Phacops are classified in part by the number of columns of elements in their compound eyes. In marine sediments from the Devonian (the middle of the Paleozoic) of Pennsylvania and Ohio, a species with eighteen columns in its eyes occurred for a while. Then, a time gap or unconformity occurred, from a temporary drying of the sea. When the sea returned and began depositing sediments again, the trilobites that returned with it had seventeen columns in their eyes. Not a huge jump, but an apparently sudden one. But wait—over in a small part of New York, the sea did not dry up. There, you can find the old eighteen-column trilobites, then some with seventeen columns plus a partial column containing a varying number of elements, and finally the seventeen-column trilobites. The generations of trilobites changed gradually, and you can see this where the rock record is complete in a small region of New York. In the bigger areas, the record looks more catastrophic because the seaway was dry and no fossils were produced when the changes were occurring through the generations living in New York.

Fossil of the trilobite Phacops rana, the State Fossil of Pennsylvania

Credit: Phacops rana by Didier Descouens, CC BY-SA 4.0, via Wikimedia Commons

You may meet someone who argues that no transitional fossils are known. This is wrong; extremely fine gradations are known in many, many lineages, including the Phacops eye columns. There is one technical sense in which, in some lineages for which fossils are scarce, there are missing transitional types. Suppose you find young fossil type 1 and old fossil type 0. They differ a good bit—you are missing the transitional form 1/2. Now suppose you find type 1/2. It is your “missing link”. You publish your results in important scientific journals, and wait for the fame and fortune to roll in. (You are likely to wait a looooooong time….) But, while you’re enjoying your discovery, someone argues that you haven’t really found the missing link, because now there are TWO transitional types missing: 1/4 between 0 and your newly discovered 1/2, and 3/4 between your newly discovered 1/2 and 1. So, you go back to work, and after years of effort, succeed in finding both 1/4 and 3/4. Wow! Now your critics point out that you are missing FOUR transitional forms (1/8, 3/8, 5/8, and 7/8). This can be argued to absurdity; we cannot find remains of every creature that ever lived, because almost all remains of almost all creatures are recycled by the efficient ecosystems of Earth (dead things are food to scavengers, worms, bacteria, fungi, etc.). But for many, many fossil types now, the gaps are vanishingly small, and the transitional forms are very well known.

The gaps in evolutionary lineages are especially well-filled for commonly fossilized types, such as creatures with shells from shallow ocean water. Shells are hard and resistant—they’re really rocks already—and so shells are preserved well. Sediments from the deep ocean are often lost down subduction zones, but shallow edges of continents are often preserved, with their fossils, for very long times. And while most of the land is eroding, most of the ocean is accumulating sediments.

The fact that most of the land surface is eroding complicates the study of the fossils that especially interest people. Think about central Pennsylvania for a moment, where Dr. Alley was sitting when he wrote this. The Commonwealth of Pennsylvania has about 1 million deer, roughly half bucks and half does, and each buck has two antlers, so Pennsylvania deer drop about 1 million antlers per year. If antlers were “preserved,” then after even a few thousand years of this, walking in the state should be dangerous, and we should hear about all sorts of antler puncture wounds from the billions of antlers scattered over the landscape. Of course, we don’t—mice, porcupines, and other creatures eat the antlers for the minerals in them. (People even collect a few shed antlers, but other creatures beat us to most of the antlers.)

In central Pennsylvania now, the only places you can find sediments being deposited are in the human-built reservoirs (which were mostly formed when dams were built in the 1930s, and so give very, very short records), a very few marshes such as Bear Meadows up the road from Penn State's University Park campus (this marsh formed during the Ice Age and thus is geologically very young), and in a few caves and along a few streams. But, the caves and stream deposits don’t last long—the caves are lost as the surface is lowered, and the streams sweep across their flood plains and move the sediments on. So central Pennsylvania today is not making much of a fossil record.

Despite difficulties such as this, careful study around the world has filled in many of the details of the fossil record, including many “missing links.” (In 2001, for example, road-builders accidentally discovered Riverbluff Cave in Missouri, with loads of ice-age fossils that offered a new window into that interesting time.) For some types of creatures, such as hominids, fossils are still scarce enough that a new find often makes headlines, and may cause a small change in the prevailing view of evolutionary history. And there was lots of excitement in 2008 when fossils of transitional flatfish were found—Darwin had worried about the way flounders evolved so the adults have both eyes on the same side of their heads, so the discovery of the transitional forms was another in the long string of successes for the theory he advanced. However, you almost never read about the great changes in thinking caused by the latest snail fossil—the record is so wonderfully complete that new insights are much harder to come by than they used to be.

The Facts and Theory of Evolution

At the start of this Module, you watched evolution occurring on a plate. Evolution has been observed in many other ways. These occurrences of evolution are facts.

Our understanding of evolution is more than these facts, though. Evolution places facts and laws, such as the law of faunal succession, into a larger context. Evolution has been tested and confirmed repeatedly, and predicts as well as explains. Evolution helps us understand what is going on, and helps us use that knowledge to do things that help people. Evolution, like relativity and quantum mechanics, is a scientific theory, the highest level of scientific understanding. The theory of quantum mechanics was used to design your computer and your phone, the theory of relativity is in your phone correcting the GPS data so you know where you are with great accuracy, and the theory of evolution is being used to fight diseases and keep you alive. Please note that calling evolution a scientific theory does NOT mean that it is speculative or uncertain, but that it is highly reliable.

The basis of evolution is diversity. (Modern social scientists and politicians are about 4 billion years behind nature on this one.) We know that kids do not look exactly like their parents—offspring are diverse or different. We also know that kids share more characteristics with their parents than with less-closely-related people from the parent’s generation. That is, we look a lot like our parents, but we are not exact copies. This arises because of genetics; the biological instructions or programs that guide the development of an individual are passed down from the parents, but there are many mechanisms active that serve to experiment a little with the instructions between generations, but not too much.

Suppose that one of these small experiments is successful (say, it gives a young giraffe a longer neck than her neighbors, which allows her to reach leaves that are out of reach of other giraffes). The long-necked giraffe will be better-fed than others and eventually is likely to succeed in surviving to have babies of her own. Some of those babies will grow a little taller than their mother, some a little shorter, and some the same height as their mother, but the offspring will average taller than the kids of other giraffes lacking the initial, successful change.

Those other giraffes lacking this new development will be less successful, and so will leave fewer babies who go on to have babies. Most populations are small enough that, if one individual is even slightly more successful than others, after a few thousand generations, all the survivors will be related to the one with the successful experiment; if one individual is even slightly less successful than others, after a few thousand generations it will have no survivors. You can demonstrate this easily using mathematical models, or with greater difficulty by breeding living types such as fruit flies, but both reach the same answer. Scientists have indeed been successful in causing evolution in the lab, and observing it in the wild. The evolution of antibiotic resistance that you watched at the start of this Module is one small example.

Once all of the members of a species contain the successful experiment, the species has been changed a little. But over those thousands of generations, other “experiments” are conducted, some successful and some not. The slow accumulation of successful experiments is evolution. The mechanism by which the changes accumulate is called natural selection—beneficial experiments allow more survival and reproduction and so are preserved and multiplied. When enough changes have accumulated, we say that a new type or species has emerged. (If a population is split into two or more parts, those parts are called new species when they no longer can interbreed.)

Notice that things that happen to adults, such as having their ears pierced or their behinds tattooed or stretching their necks to reach leaves, are not passed on to children. The changes that are passed on occur during reproduction. Sex helps generate new combinations of genetic instructions. Even species that reproduce asexually by splitting in half have ways (proto-sex?) to exchange genetic material. Sometimes, accidents occur owing to radioactive decay or toxic chemicals damaging the genetic instructions in an egg or sperm or asexually reproducing creature; however, these often are changes that hurt rather than help.

More importantly, the mechanisms of reproduction do experiment a little by moving a few things around in the genetic instructions during reproduction. Some species, and some individuals of species, conduct more experiments than others. Overuse and misuse of antibiotics by humans are producing antibiotic-resistant disease-causing organisms. These antibiotic-resistant types are often those that experiment a lot during reproduction, and so were lucky enough to quickly find an experiment that allows survival despite antibiotics.

The virus HIV that causes the disease AIDS is especially hard to “beat” with a vaccine or antiviral drug because the virus experiments a huge amount (perhaps the fastest known rate of mutation). It took decades for a large number of dedicated researchers to come up with a “cocktail” of drugs that gives long-term survival to HIV-infected patients. The rapid rate of experimentation in HIV is costly to the virus—many of the experiments are failures, which means those offspring don’t succeed. But, this high rate of experimentation allows the virus to respond quickly to challenges such as new drugs or vaccines by producing offspring with new ways to defeat those drugs or vaccines. In an AIDS patient, the viruses infecting different organs may be different. And, given that the AIDS viruses in just one person are so diverse, it is not surprising that the viruses in different people are different. The remarkable advances in molecular biology allow these changes to be measured now, but no effective vaccine has yet been developed to help people completely clear HIV.

Evolution is a well-tested, well-established science. It makes predictions that are borne out every day. Partial speciation has been achieved in the laboratory in fast-breeding types such as fruit flies. The geological evidence of gradual changes is strong, and becoming steadily stronger as more and more samples are collected.

Evolution is also being used routinely in science. The Evolution on a Plate video showed one reason why. A search on the ISI “Web of Science” in July of 2012 revealed over 3000 scientific papers on the subject "evolution and antibiotic resistance," with an ongoing rise in the number of papers on the topic. The same search in 2024 found almost 10,000 scientific papers. A quick perusal of the titles and abstracts of many of those papers revealed that, as microbes evolve to defeat our antibiotics, the scientists who are trying to keep us alive are using the tools and language of evolutionary biology. Antibiotics are quickly losing effectiveness against evolving microbes, and without major efforts, more and more people would be dying of infections picked up in hospitals, thus scientists are increasingly focusing on the problem, informed by a full understanding of evolution, its rates, and processes.

Computer scientists even use evolution—some “artificial intelligence” approaches have been patterned after the natural processes of evolution. Techniques such as genetic algorithms or evolutionary computation successfully solve complex problems, in essentially the same way that nature does. (For more on this, see the Module 11 Enrichment.) The computational pioneer Alan Turing suggested that scientists could mimic evolution to find solutions to complex problems as early as the year 1948, for example.

In the U.S., some groups continue to oppose evolution based primarily on religious grounds. This opposition has the good effect of keeping the experts “on their toes”—the experts work harder and do better science. This opposition has the unfortunate effect of convincing many people that something is fundamentally wrong with evolutionary theory, which may scare some students from entering the field and helping save lives, and may cause some people to ignore scientifically based advice and thus endanger themselves and others. Many of these people seem to believe that evolution is somehow anti-religious when the majority of church members in the U.S. belong to denominations that endorse evolution as the best description of how the biological world works. Evolution is consistent with the major religions on Earth, and even with rather strict readings of the Christian Bible. The idea that the Earth appears young, and was created recently with all of the modern types of organisms present, was tested in the 1700s and 1800s and proved wrong, as we saw in Module 10.

A longer discussion of some issues—how evolution can be consistent with religion, how evolution is consistent with the second law of thermodynamics, why "intelligent design" is not science, etc.—is given in the Enrichment. We strongly suggest that if you are interested in this topic, you read Module 11 Enrichment.

Extinction and Dinosaur National Monument

Dinosaur National Monument Location

Credit: R. B. Alley © Penn State
is licensed under CC BY-NC-SA 4.0

Dinosaur National Monument lies in western Colorado and eastern Utah. The key rocks were deposited in swamps and along rivers during the Jurassic in the middle of the Mesozoic, and are called the Morrison Formation. Before the modern Rockies were raised, sluggish streams flowed across the basins of this region, with numerous low, wet floodplains. Dinosaurs flourished. After some died, their bodies were washed up on sandbars, where their bones were buried before scavengers and gnawers could consume the bones. Over time, minerals carried in groundwater reacted chemically with the bones, depositing silica in them. (For a little more on petrification, see the Module 11 Enrichment—no magic is involved, and replacement by stone is a normal process that really is expected to occur in some places!)

Dinosaur bones in the high wall of the Dinosaur Quarry Visitor Center at Dinosaur National Monument. Visitors can see and experience how much hard work goes into the extraction, preparation, and study of fossils. There are displays illustrating some of the methods that paleontologists use to interpret how the dinosaurs lived and interacted with their environment.

Credit: Dinosaur National Monument - Dinosaur bones in the Dinosaur Quarry, from Geology and Ecology of the National Parks, USGS (Public Domain)

After the bone was turned to stone at what would become Dinosaur National Monument, the rocks of the region were raised and tilted during the mountain-building that formed the Rockies. Streams, including the Green River, cut through the rocks. The Canyon of Lodore on the Green is a favorite destination for serious white-water rafting. The first scientist in the region was John Wesley Powell, who went on to run the Grand Canyon. In 1909, workers from the Carnegie Museum of Pittsburgh found Dinosaur Ledge, a sandbar-turned-to-stone on which many dinosaur bones had been deposited and fossilized. Today, some of those petrified bones are on display in the Carnegie Museum and in other great museums, but many of the bones have been left on the ledge to be viewed in the park (see the picture above).

How Did We Get Dinosaurs?

The history of life on Earth is amazing, and much more has happened than we can possibly cover in this course. We will, however, give you a very short sketch of a few of the key events. You might watch the following short narrated video first (Evolutionary Process).

Video: Evolutionary Process (3:20 minutes)

We don’t really know exactly how or when life started, but the geological record includes evidence of life almost as soon as conditions developed that could support life as we know it, perhaps as early as 4 billion years ago. Life mostly remained in the sea for much of Earth’s history, because life is water-based and tends to dry out on land. Before the start of the Paleozoic about 530 million years ago, most living things remained small and slow-moving, probably because oxygen remained scarce in the atmosphere. We get our energy by “burning” food with oxygen to release energy, and without oxygen, we couldn’t release energy rapidly from our food. The history of oxygen in the atmosphere is fascinating, with fluctuations caused by changes in tectonics and climate and evolution, and those changes affecting biodiversity; some of the important work was done by Penn Staters, but again, the details are for another course.

After oxygen finally became consistently common in the atmosphere, with plenty of dissolved oxygen in the ocean, large and active creatures evolved “quickly”, over 10 million years or so. Many of these had shells, which are preserved well as fossils, so the fossil record of life became much more interesting. The 10 million years of this “Cambrian explosion” at the start of the Paleozoic are not exactly an explosion, but after 3.5 billion years of small, rare fossils, a large increase in just 10 million years seems fast.

Through the Paleozoic, life spread onto land, large and agile animals evolved, trees evolved, and more. As life became more diverse, some species went extinct while new ones evolved. But, at least twice during the Paleozoic, and at the end of the Paleozoic, and once during the Mesozoic there were “mass extinctions”, when a lot of species went extinct in a short time, reducing biodiversity. Then, over millions or tens of millions of years, new diversity evolved.

We are not going to make you learn the details of these older mass extinctions (we’ll cover the one that killed the dinosaurs soon…). You should know that these older mass extinctions were primarily caused by climate change, and especially by extreme warmth from release of carbon dioxide from really large flood basalt volcanic eruptions (we visited this subject way back in Module 3 with Hawaii). The heat from the extra carbon dioxide reduced the dissolved oxygen in the ocean, and the ocean may have been overfertilized by rapid weathering of the new volcanic rocks, leading to “dead zones” and release of poison gas (hydrogen sulfide). The worst of these extinctions, at the end of the Paleozoic, involved temperatures too high for large animals to survive in the tropics on land and in the ocean, and may have killed 90% of the species on Earth at the time.

(We will revisit this issue of climate change and carbon dioxide next time, in Module 12. The release of carbon dioxide that drove these extinctions was as large or larger than what humans might do if we burn all the fossil fuels, but was much slower than we might do, giving prehistoric life more time to adapt. And, we do know that the modern rise in carbon dioxide is being driven entirely by humans, not by volcanoes.)

After each mass extinction, many “jobs” (often called ecological niches) opened up because the plants and animals that had been doing those jobs were all dead. The new species that then evolved often filled the old jobs, but in interesting new ways. The earliest dinosaurs evolved as diverse life returned after the worst extinction that ended the Paleozoic.

The dinosaurs were the dominant large animals on Earth for over 100 million years. Many were quite small, but some were gigantic. They included large plant-eaters and large meat-eaters. Some spent at least part of their time flying or gliding, and others swam.

Virtual Field Trip: Dinosaurs: Where They Lived, and How They Died

Virtual Field Trip: Dinosaurs: What They Stepped In

What Killed the Dinosaurs?

The “Dinosaur Quarry” at the Dinosaur National Monument straddles the Colorado-Utah border. Bones of many dinosaurs are exposed here, still in the rocks where they were fossilized.

Credit: R. B. Alley © Penn State is licensed under CC BY-NC-SA 4.0

Mammals co-existed with the dinosaurs for most of the dinosaurs’ existence. However, almost all of the mammals remained small creatures—they generally could not outcompete the dinosaurs for the big-creature jobs.

Extinction is a normal process. A new species may arise and be more successful than an existing type, pushing the old type to extinction. Diseases, accidents, or other events may kill an entire population. And, extinction is forever. As populations vary owing to random factors, sometimes the population drops to zero. But when the population hits zero, the species can never come back up—you can’t just borrow a few creatures from a future generation and bring them back to fill in the gap. So all sorts of random events cause extinctions, and most of the species that have lived on Earth have become extinct. (This characteristic of extinction, that when you hit zero, you're gone, also applies to gamblers at casinos. To see why you’re likely to lose if you gamble, take a look at Module 11 Enrichment.)

About 65 million years ago, at the end of the Cretaceous Period of the Mesozoic Era and the start of the Paleogene Period of the Cenozoic Era (the K/Pg boundary, because K is used for Cretaceous and Pg for Paleogene; note that old literature used Tertiary rather than Paleogene and called this the K/T boundary), a very large extinction event killed most of the living dinosaurs except for the birds. At the same time, many other types became extinct—more than half of the species known from fossils near the end of the Cretaceous became extinct at the end of the Cretaceous. Because the survival of even a few individuals from a species can allow the species to persist, it is likely that almost all living things on the planet were killed. It was a catastrophic event, one of the most catastrophic in the history of the Earth.

The solution to this puzzle—how the dinosaurs and others were killed—was not found until fairly recently, but now we have a lot of important data. At the K/Pg boundary, sedimentary rocks around much of the world contain a thin clay layer. This layer is rich in iridium, an element rare on Earth but common in meteorites. This clay layer contains bits of rock that were melted and refrozen rapidly to form glass, such as are produced by meteorite impacts. Quartz grains in the layer contain shock features, which are caused by very high pressures applied very rapidly, but by no other known mechanisms such as volcanic eruptions. The layer is rich in soot (black carbon) from fires. The layer is thicker in and near the Americas than elsewhere. Around the Caribbean Sea, the layer includes a deposit of broken-up rock such as would be produced by a huge wave. And, on the Yucatan Peninsula is a large crater, the Chicxulub Structure, that is dated to the K/Pg boundary. The crater is partially buried by younger rocks but easily detected using geophysical techniques, drilling, etc. The crater is at least 110 miles (180 km) across, and perhaps as much as 180 miles (300 km) across.

This evidence indicates that a large meteorite, perhaps 6 miles (10 km) across, hit the Earth (the hole or crater made by an energetic projectile is usually a whole lot bigger than the projectile). Such a collision would have released more energy than all of the nuclear bombs that were on Earth when the U.S. and Soviet arsenals were at their largest.

The impact broke huge amounts of rock into small pieces, from the meteorite and from the Earth where the meteorite hit, and melted much more rock, blasting the solid pieces and melted drops of rock into the air and even above the atmosphere into space. As large pieces fell rapidly back to Earth, friction with the air generated heat in the same way that a re-entering space capsule or a “shooting star” is heated. For a little while, the air would have been like a toaster-broiler oven, lighting wildfires around much of the Earth that produced the soot in the fallout layer and that killed many things.

Following that, cold and dark descended. The impact site included sulfur-rich rocks. The heat of the impact vaporized some of those rocks, and that vapor cooled later to form sulfuric-acid clouds in the stratosphere. The small particles of these clouds didn't fall fast enough to heat up much, just as raindrops and dust particles do not heat up when they fall today. The many, many small particles, plus fine dust and soot from the fires blocked the sun and cooled the Earth. We know that such cooling occurs with modern volcanic eruptions—big ones such as Mt. Pinatubo in 1992 cool the Earth by a part of one degree for a year or two. A nuclear war might do much more, creating a nuclear winter or at least a nuclear fall. Even more of the sunlight would have been blocked after a huge meteorite impact, and the world may have frozen for a few years. And, with the sunlight blocked, photosynthesis would have stopped, which would have been very bad for plants that rely on photosynthesis and animals and fungi that rely on plants.

The sulfur particles, when they fell, would have made sulfuric acid, giving much stronger acid rain than the recent human-produced pollution. The sulfur in the stratospheric may have damaged the ozone layer, allowing dangerous UV radiation to penetrate as the dust and soot started to clear.

The impact site included a lot of carbonate rocks, and those broke down in the intense heat, releasing carbon dioxide. After the dust and sulfur cleared and the freezing ended, the world became anomalously hot for perhaps 100,000 years or so, from the enhanced greenhouse effect caused by all that carbon dioxide.

Dinosaur Footprints, Dinosaur Ridge, Colorado. The dinosaurs that made these were still very much alive, well before the meteorite hit.

Credit: R. B. Alley © Penn State is licensed under CC BY-NC-SA 4.0

The meteorite impact was not nearly big enough to roll the Earth over, notably move the orbit, rearrange the continents, or anything similarly cataclysmic for the physical behavior of the planet beyond the few years or decades of the heat, cold and acid — the energy brought by the impactor was enough to move the Earth in its orbit roughly 1 cm, or a bit less than ½ inch, NOT dramatic. But the event was cataclysmic for life—almost all of the living things on Earth died. Who survived? Plants with long-lasting seeds, hibernators, things that live in ocean sediment or along spreading ridges, scavengers, and probably some others with appropriate characteristics. The general pattern is that the surviving animals were small, and mammals did better than dinosaurs. (Although, yes, birds are a branch of the dinosaurs, and the birds are still with us.)

After the fire and ice was over, the “jobs” (ecological niches) of many of the dinosaurs were left open. There were no big plant eaters or big meat eaters left, for example. Over tens of millions of years, the mammals, freed of the competition from the large dinosaurs, slowly evolved to take over the jobs of the dinosaurs. Some of the larger offspring of some species were successful, although most mammals remained small (mice, voles, etc.). Lining up the fossils over time, we see an evolutionary shrubbery—lots of branches, many extinctions where those branches were cut off, the persistence of small creatures, but the appearance of some large creatures, with those leading to modern lions and tigers and bears—and people. Biodiversity was hugely reduced by the meteorite, but over the next millions of years, new species appeared a little more often than existing species went extinct, so that diversity increased back to more-or-less what it was before the meteorite, just with different species doing the jobs.

If today, Coke and Pepsi and all other soft-drink companies suddenly magically disappeared, new soft-drink companies would be started fairly soon, not because of a magical tendency for soft-drink companies to appear, not because soft-drink companies must exist, but because we usually figure out how to take advantage of opportunities. In the same way, wiping out dinosaurs opened up a space for the evolution of mammals.

More on Meteorites and Mass Extinctions

Meteorite impacts have been happening throughout Earth's history, and a Mars-sized body colliding with the Earth and blasting things into space is the best explanation for the formation of the moon. Big impacts were common early on in Earth's history. Penn State's Evan Pugh University Professor Jim Kasting (since retired), helped show that the heat from many of the huge impacts during the first few hundred million years of Earth's existence would have been enough to evaporate the whole ocean, and that as recently as about 3.8 billion years ago impactors may have been big enough to evaporate the sunlit upper layer of the ocean. Since then, collisions have been much smaller. The dinosaur-killer was larger than any others that fell to Earth during the most recent ~2 billion years (with some slight uncertainty because the record of an old event that hit entirely in the ocean might have been subducted), but the energy released by the dinosaur-killer was probably only enough to evaporate an inch or two of the ocean (a few centimeters). Even so, the dinosaur-killer wiped out a lot of species only because it hit special rocks that contained abundant sulfur and carbon. If other similar-sized meteorites had hit the Earth, almost all of them would have failed to cause a similarly large mass extinction, because almost all of them would have hit rocks that would have had less influence on the climate.

Please note that almost every major event in Earth’s history has been blamed on a meteorite by somebody at some time. Then, in almost all cases, additional scientific research showed that a meteorite was NOT responsible. The meteorite hypothesis then should have been moved to a footnote or dropped entirely. But… in online searches, the meteorite hypothesis lives on, waiting to trap unsuspecting individuals with outdated or inaccurate information. Often, one or a few scientists continue to push the idea, or nonscientific groups take over that job. Here, we have tried to give you the best information, representing an immense body of scientific work.

So, in the last couple of billion years, we have evidence of only one huge event in Earth’s history that was caused by a meteorite impact. But, smaller meteorites have caused small events, and many large rocks still are whizzing around out in space, so large impacts remain possible. An event like the one that formed the Meteor Crater, Arizona (see the picture below), which is 3/4 mile across, would be catastrophic for anyone living in or near the impact site, even though it would not have global consequences.

Meteor Crater in Arizona. The visitor's center is at the top of the image. Note vehicles in the parking lot for scale.

Credit: USGS National Map Data Download And Visualization Services. Caption By Robert Simmon

One scientific estimate found that your chances of being killed by a meteorite impact are about the same as being killed in the crash of a commercial airliner. Commercial airliner crashes kill a few hundred people per decade, and a meteorite might wait ten million years and then kill hundreds of millions of people, so the statistics are hard to compare, but the number is interesting. In comparison, recent statistics indicate that roughly 1.5% of deaths in the USA are from guns, and slightly over 1% from car crashes and other transportation-related fatalities. All other “accidental” deaths are much, much rarer but often get more press coverage, including tornadoes, hurricanes, earthquakes, food poisoning, bee stings, shark attacks, and many others. Part of this is because we have taken precautions against many of these others, such as accurate weather forecasts that allow millions of people to get out of the way of hurricanes. In the long term, smoking, over-eating, under-exercising, and other poor health habits are more important triggers of early death.

Scientists are coming up with ways to divert asteroids that might hit us, to help avoid such collisions. If we see an asteroid coming from far enough away, we need to turn its path only a tiny bit to miss the Earth. One idea is to hit the asteroid with a bag of dust that would spread across one side, changing the reflectivity of the surface; the difference between reflecting and absorbing the sunlight would cause a tiny push that would steer the asteroid. Another idea is to send a spacecraft to sit next to the asteroid for a year; the tiny gravity of the spacecraft, tugging on the asteroid, would turn it a tiny bit. In the year 2022, NASA proved that they could change the orbit of an asteroid by hitting one with a "kinetic impactor" Planning to avoid the fate of the dinosaurs may save us someday.

Really, despite the immense drama of the meteorite that killed the dinosaurs, and its critical role in the events that led to us, other issues are more important now. Let’s go visit a few of those, in the Arctic and Yellowstone, in Module 12, after you have a chance to explore the Enrichment.

Petrified Forest National Park

Here are some enrichment items from the CAUSE class visiting the Petrified Forest, a truly wonderful place.

Virtual Field Trip: Hardwoods—CAUSE and Park Paleontologist William Parker Explore the Petrified Forest

The fossil record includes some amazing things. If there were trees and insects far back in time, wouldn't you expect that the insects would have burrowed into the trees then as they do now? And wouldn't you expect that a tree with some of those burrows would be fossilized? Well, here is one example. Park Paleontologist William Parker of the Petrified Forest National Park explains fossil burrows to the CAUSE team.

Video: Ancient Bee's Nests, Petrified Forest National Park (1:56 minutes)

Petrified Forest National Park is best known for trees turned to stone, but also has an immense wealth of fossils of various types from the late Triassic (in the Mesozoic, about 210 million years ago). Here, Park Paleontologist William Parker and assistant Randall Irmis explain to the CAUSE class the paleontological excavation of plates of the armored amphibian known either as Koskinonodon or Buettneria.

Video: Uncovering Fossils - Petrified Forest National Park (2:58 minutes)

Deep Time (repeated optional content)

What do beauty, saving money at Las Vegas, religion, oil exploration, emerging new diseases, and the planet’s recovery from global warming have in common? All in some way involve deep time, the immense age of the Earth. Eric Spielvogel filmed a discussion of these and other issues with Dr. Alley, for a special “time” issue of Research! Penn State. These "Deep Time film clips" will give you something to think about, and may even help with the course. Enjoy!

During three weeks in May 2004, two hardy Penn State geoscientists traveled through 12 stunning National Parks of the southwestern United States with 13 lucky students. The trip was sponsored by CAUSE (Collaborative Active Undergraduate Student Experience), an annual course offered by the College of Earth and Mineral Sciences. Richard Alley, Evan Pugh professor of geosciences, led the expedition. CAUSE 2004 was an extension of his course, "Geology of National Parks," and allowed students to interact with and learn from the rocks and landscapes of Arizona, Utah, and Colorado. In the following videos, Alley explains the concept of deep time, how it tells the history of our planet, and how it affects our lives.

Richard Alley, Ph.D., is Evan Pugh professor of geosciences in the College of Earth and Mineral Sciences, rba6@psu.edu.

—Emily Rowlands

What is Deep Time? (2:44 minutes)

Deep Time and Beliefs (1:28 minutes)

Deep Time and Climate Change (1:34 minutes)

Deep Time and You, Part 1 (1:16 minutes)

Deep Time and You, Part 2 (2:16 minutes)

Optional Enrichment Article #1

More Insight into Evolution

Many very good sources are available on evolution. The interested reader may wish to start with Teaching About Evolution and the Nature of Science (1998), National Academy of Sciences, National Academies Press, Washington, DC.

What follows, in question-and-answer format, is a synopsis of some of the objections that the author, Dr. Alley, has heard or read against evolution, together with brief answers. The author expresses some opinions toward the end on the teaching of science, but they are quite in line with the broader scientific view and with materials already discussed in class. The author really believes that science is a tremendously useful way for humans to find out how the world works to help us stay fed and clothed and housed and healthy so that we can address big questions. The author also includes quotes from two noted people (Pope John Paul II and US President James Earl Carter) that tend to promote religion as well as science, but this does not mean that this course is promoting or discouraging religion, just that these are part of the discussion.

Question: Is evolution anti-religious, or religion anti-evolution?

Answer: They don’t have to be. The author is religious and is convinced of the overwhelming scientific evidence for evolution. When the author wrote a commentary on the subject for Pennsylvania newspapers, the pastors at the author’s church (a mainline Protestant denomination) approved of the piece. Most of the religious people in the U.S. belong to groups that have accepted evolution. Pope John Paul II added the Catholic Church to those groups accepting evolution (“Truth cannot contradict truth;” Address of Pope John Paul II to the Pontifical Academy of Sciences, October 22, 1996).

Perhaps the most famous Sunday School teacher ever in U.S. history, former president James Earl (“Jimmy”) Carter, said in January 2004 that “he was embarrassed by the Georgia Department of Education proposal to eliminate the word ‘evolution’ from the state’s curriculum” (CNN story). He went on to say, “The existing and long-standing use of the word ‘evolution’ in our state’s textbooks has not adversely affected Georgians’ belief in the omnipotence of God as the creator of the universe. There can be no incompatibility between the Christian faith and proven facts concerning geology, biology, and astronomy. There is no need to teach that stars can fall out of the sky and land on a flat Earth in order to defend our religious faith.”

There surely are people who believe in evolution and who dislike or even attack religion, and there are many religious people who dislike or attack evolution. But, evolution is not anti-religious in any way. The author is of the opinion that most leaders of evolutionary research wish to coexist with religion, and that most religious leaders wish to coexist with evolution.

Question: Doesn't evolution lead to Hitler, ethnic cleansing, or the killing of innocent misfits?

Answer: Very often, “what is” becomes entangled with “what ought to be”—“Letters to the Editor” on the subject frequently include the worry that science displacing religion inevitably leads to a lack of divine authority for moral codes, which leads to a lack of morality. As noted above, this just doesn’t make sense—evolution-accepting Jimmy Carter and Pope John Paul II were highlighted as truly moral people. (But, the author suspects that questions of morality are more important than questions of science to many of the critics of evolution.)

In regard to racial purity or some similar such nonsense, consider for a moment the case of the author. He peers out from behind thick glasses, and his daughters both wear corrective contact lenses. He likely has a genetic predisposition causing near-sightedness in individuals who, while still young, use their eyes for much close-up work such as reading. This genetic predisposition seems to be hereditable—he has passed it on. (There is still medical debate about the genetic roots of bad eyesight, but the interpretation here is probably correct.) Leaving the author in the gene pool may “weaken” it a little bit. How should the author be dealt with in a world that recognizes evolution? Should he have been sterilized as a youth, or killed, or forbidden to mate? Or, should he be recognized as suffering from a handicap for which he should receive affirmative action? The government could have subsidized lessons for him during his youth on how to be attractive to a potential mate while peering through thick glasses. (Fortunately, he was successful in marrying a wonderful woman, but maybe other downtrodden thick-glasses wearers should have been helped by outreach efforts.) Or, should we just recognize that glasses (and now, contacts) work just fine, and why worry about it? The reality of evolution in no way dictates one’s morality! Evolution is what is, not what ought to be—we have to decide how to use the scientific information about evolution.

Question: Don’t the gaps in the fossil record prove that evolution did not occur?

Answer: No. We covered this one in the text at some length; the fossil record is beautifully consistent with evolution. The gaps present are the gaps expected based on the nature of speciation and the incompleteness of the fossil record, and the gaps are filled by transitional forms in those groups that are commonly fossilized and for which you would expect to find transitional fossils. Even a little consideration shows that not every creature is fossilized, and that big and relatively rare land creatures will have somewhat sketchy fossil records whereas small and relatively common shelly shallow-sea creatures will have rather complete fossil records. This is observed. One can look at the likelihood of fossilization, and then generate predictions on how complete the fossil record will become as more fossils are collected, and these work.

Question: Aren’t there lots of problems with age dating, showing that the world is really young?

Answer: Again, this was discussed a lot back in Module 10. There are commentators who make such anti-science arguments that might seem sensible to those who don’t know the field, but those arguments can be shown to be completely wrong with just a little care.

Consider one that the author has shown several times. The author has helped count over 100,000 annual layers in a Greenland ice core and participated in numerous careful tests using the fallout of historically dated volcanoes and other time markers to show that the results are reliable. The “counter-argument” from the young-Earth supporters was that a flight of World War II planes that were forced to land on the ice sheet had been buried a couple of hundred feet in only 50 years, so a couple of thousand feet would be 500 years, and the 10,000 feet of ice thickness in central Greenland would be about 2,500 years, so the ice sheet started safely after Noah’s flood. Seems perfectly reasonable, doesn’t it?

But, when we discussed glacier flow back in Module 7 we noted that a glacier is a bit like pancake batter, spreading across a griddle under the influence of gravity. If you put a dollop of pancake batter in the middle of a griddle and watch, the layer thins as it spreads. Put another dollop on top, and both spread and get thinner. Keep putting dollops on top, and letting the batter drip off the end of the griddle, and eventually, you’ll have a whole pile of layers. The one at the bottom will have been spreading and thinning the longest and will be the thinnest.

An ice sheet is similar, spreading and thinning as more snow is piled on top. Very crudely, an annual layer will become half as thick and twice as long while it is moving halfway from wherever it is toward the bed. Friends of the author have directly measured the motion and spreading of the ice, and it fits this pattern beautifully. (These measurements show a little extra downward motion associated with squeezing snow to ice, but glaciologists usually speak in terms of ice-equivalent thickness—the air already mathematically squeezed out. And very deep, the halfway-to-the-bed-thins-by-half breaks down, because the ice sheet had to form sometime so the first layers weren’t thinned while flowing through the ice sheet, and because the flow over bumps in waffle-iron fashion also complicates things a little). The fact that Greenland makes icebergs and hence is spreading means that deeper layers are thinner, and the simple airplane burial calculation is completely wrong.

At the time the author was writing this, a quick search of the Web found numerous sites that slightly improved the young Greenland calculation while still getting it completely wrong. These sites noted the thinning of layers with increasing depth, picked a place near the edge of the ice sheet where the ice was relatively thin, picked a thickness of annual layers at the surface, picked an erroneously thick annual value at the bottom, and suggested using the numerical average of the surface and bottom thickness in the calculation to get the age of the ice sheet. Fourteen inches thick at the top, less than two inches thick at the bottom, call it two inches, take the average of 14 and 2 inches and get 8 inches per year, and a few thousand feet of ice in the thin margin of the ice sheet will still squeak in after Noah’s flood—the scientists must be confused. Seems reasonable, right?

Absolutely not. Try this very simple equivalent, that you can do in your head. Suppose that the ice sheet is two feet thick, or 24 inches, that the top annual layer is 12 inches thick, and the bottom has twelve annual layers each 1 inch thick. A scientist would count the annual layers and find 13, giving a 13-year age for the ice sheet. But the technique advocated by the young-Earth websites would average the top and bottom thicknesses (6.5 inches per year), and then calculate that fewer than 4 years were required to build up the two feet of ice, not the actual 13 years. The mathematical error made on the websites is a very simple one and one that most students will have learned to avoid while still in middle school. (The author doesn’t know whether the mistake on these young-Earth websites represents stupidity or deliberate misrepresentation, but the mistake is so flagrant that it is not easy to think of a third option.) Do the calculation right for Greenland, and you end up with a very old ice sheet. If you count the annual layers or calculate the age using the flow of the ice sheet, estimate the age by identifying abrupt climate changes and using the ages from counting tree rings or other annual layers, or use any of the other dating techniques, you’ll get the same answer: Greenland’s ice is much older than written history.

The scientific community is continually improving age-dating techniques, arguing about them, and working on them, and thus far, no serious problems have been found with the old age of the Earth. The arguments presented against the old age, such as the buried planes or the 5,000-year-old living clam (see the Enrichment from the Grand Canyon in Module 10) prove not to be problems after all.

Question: Doesn’t the second law of thermodynamics prove that evolution cannot have occurred?

Answer: No; evolution is fully consistent with the second law of thermodynamics. The second law says that entropy (disorder) increases in a closed system. Evolution sometimes makes more complex things from less complex ones, which might seem to violate the second law. But, evolution is done with the addition of energy from the sun; the Earth is not a closed system. The living and evolving creatures take complex food and burn it with oxygen to gain energy, increasing disorder. Some creationist websites have even suggested that followers avoid using this second-law argument because it is so completely and obviously wrong.

An interesting note is that a whole field of Evolutionary Computing now exists (linked to genetic algorithms, artificial intelligence, etc.). In trying to “teach” computers to solve complex and difficult problems, computer scientists have found it useful to mimic evolution and natural selection—have the computer start with a possible answer, see if it works, then tweak the answer and see if that works better, throwing away ones that work worse and keeping ones that work better. If, for example, you’re trying to improve the routing of airplanes to fly the shortest distance while carrying the most passengers, you could start with the current route map, and then randomly “perturb” it a little, to see if that works better. You need to define “better” (how many more miles of flying is it worth to allow you to sell another passenger ticket?), but then the technique is successful. Usually, many small perturbations are used in sequence, and occasionally a slightly larger one may be useful; but huge ones usually fail. The approach obtains order—a useful optimization of the flight plan—from the chaos of reality by random adjustments followed by selection of those that work better. Selection doesn’t require intelligence, but simply telling the computer to save the coordinates if the cost is lower. In biology, this selection is achieved by survival—if you survive to have kids, you have been selected. The lessons of biological evolution thus have been used to help computer scientists solve hard problems—science works. And the idea that somehow the second law of thermodynamics prevents evolution is just silliness.

Note that, in the absence of the “selection” step, randomly generating new options is almost guaranteed to fail in finding an optimal answer. Many of the anti-evolution websites and other anti-evolution materials point to how incredibly unlikely it is for random processes to generate something useful. These sites are completely correct, but completely misrepresent evolutionary theory. In evolution and evolutionary computing, the step of randomly generating lots and lots of new “experiments” is followed by the step of picking “successful” ones—in evolutionary computing, the successful ones meet some criterion such as saving the airline money; in evolution by natural selection, the successful ones promote survival to have kids.

Question: Isn’t evolution restricted to the “micro-evolution” that we can see (such as breeding tiny white dogs from larger, grayer dogs), and cannot include “macro-evolution” of new types?

Answer: This one takes a bit of discussion; it seems common-sensical, but turns out to be really wrong.

To many biologists, evolution is defined as something like a “change in gene frequencies over time,” with genes being the basic inherited instructions for making and running living things. There is no “micro” or “macro” in this; the distinction is simply not meaningful in the modern theory of evolution. “Macro” is just more of “micro”; they are not separate things.

A different way to view this question is that, biologically, there is a division between species (either things interbreed and are thus part of the same species, or they don’t interbreeed and are a different species, or they do interbreed somewhat and pose problems for what word we use to describe them, as discussed next). All of the other divisions that we draw between different living types (kingdom, phylum, class, order, family, genus) are human constructs to help us understand the world. If different people with well-developed science had named all of the creatures, those people likely would have picked the same species but may have picked different ways to group the species. “Macro” in this sense presumably is used by the evolution-skeptics to refer to changes between the larger groupings (there are wolves and coyotes and domestic dogs, but these people claim that there is a fundamental difference between “dogness” and “catness”). But larger groupings are primarily conveniences for us; evolutionary biology addresses whether creatures interbreed and exchange genes, or not.

“No, no, no” a skeptic might say, “We don’t care about what biologists think; we care about the reality, and we know that there is ‘dogness’ and ‘catness,’ these are different types or sorts.” This is harder to answer; such people presumably are postulating some unknown barrier that somehow prevents genetic “experiments” beyond pre-defined boundaries—evolution can bring about new types of dogs, or new types of cats, but only to some boundary and not beyond. But what forms such a boundary? Where is the ‘police officer’—biochemical or otherwise—that would check after two dogs had sex to make sure that the potential offspring did not include a genetic experiment that went one DNA base pair outside of the defined limits of ‘dogness’? An omnipotent deity could of course do such a thing, but there exists no scientific evidence for this—make another base substitution in DNA, and you have another experiment. Let nature choose the “good” experiments (those that lead to lots of surviving kids) and evolution happens. “Macro” evolution really means “evolution that takes long enough to occur that humans in their lifetimes won’t see much change in large animals (although plenty of such changes are happening to disease organisms).”

Dogs and cats really are different, because many successful evolutionary experiments have accumulated over tens of millions of years. Evolution really is gradual, and “hopeful monsters” (a dog gives birth to a cat, for example) do not happen. But, given the observed rates at which variability is produced by reproduction, and the rates at which natural selection is observed to function, mathematical modeling shows that there has been more than enough time in geological history for all of evolution to have occurred. There is no problem, for example, in going from the known damage that happens to cells in the bright sun (sunburn), to cells that are a bit more sensitive to light to help a creature know where the light is and avoid it, to groupings of those cells, and on to an eye. The question is not whether evolution could have happened in that much time, but why evolution ran as slowly as it did—most of the time, not a lot of change has been occurring, probably because creatures had found pretty good evolutionary solutions to problems and tended to stick with those solutions.

An additional note is that the species with us today are really not as separate and distinct as some people might have you believe, but have blurry edges, overlaps, etc., as you would expect from the scientific understanding of evolution. For example, “ring complexes” of animals are observed—species A interbreeds with B, which interbreeds with C, but A and C don’t interbreed. Are A and C the same species? Would they be if B became extinct? (Imagine what would happen if we had nothing but miniature poodles and Great Danes—could they ever “get it on”?) The messy world of biology shows that the world is not populated by “types” but by evolving populations with greater or lesser degrees of gene exchange.

Question: What about “Intelligent Design”?

Answer: “Intelligent design” is a resurrection of a very old idea. Proponents of “intelligent design” argue that there exist “irreducibly complex” parts of plants and animals, such that these parts would not have been useful while they were evolving but only after they evolved, and thus they could not have evolved. If evolution made a useless something that later became part of an eye, that something wouldn’t help the creature and might hurt it, and so wouldn’t be saved and experimented upon to generate the rest of the eye—the intermediate steps usually should be useful for evolution to work.

In decades gone by, the eye was often cited as an irreducibly complex structure—without all of the parts of your eye, you wouldn’t be reading this. But it is very easy to find successful creatures on Earth with no eyes, others with rudimentary eye spots, and others with slightly more complex eyes, and so on—gradual improvements in the slight sensitivity of all cells to light can lead to an eye. Because each step in the evolution of an eye has utility, the eye is not “irreducibly complex”. (Ask someone whether they would prefer to be completely blind or to be able to discern light and darkness, or vague shapes, and that person is not likely to opt for blindness—less-than-perfect eyes are still valuable.) As their eye argument failed, intelligent-design advocates have switched to other arguments, such as the flagellum or the clotting of blood, but scientists working on these topics are not finding these structures to be irreducibly complex, either.

Scientists working in many fields related to evolution have been vocal through their leading organizations, such as the National Academy of Sciences, and the American Association for the Advancement of Science, in noting that “intelligent design” is not science, even if it happens to be stated by people with scientific training. Scientists after all can say all sorts of things that are not science. (And yes, you can find a few scientists saying anti-religion things, but those are not science either.) The leading hypothesis of “intelligent design” seems to be that there are some things that evolutionists cannot explain. This hypothesis does not lead to useful predictions that can be tested and falsified, so it just isn’t science. Notice, by the way, that a successful scientific explanation of one so-called irreducibly complex item such as the eye has not falsified “intelligent design” to its supporters, who can always propose that something else is irreducibly complex. In a widely watched court case in Dover, Pennsylvania in 2005, a federal court stated these results very clearly: “intelligent design” is not science. (See the Kitzmiller case (.pdf) at uscourts.gov if you’d like 139 very interesting pages on this topic.)

After the author wrote a newspaper column advocating the teaching of science in science classes (included here in Enrichment 2), he received communications (e-mail, phone, letter) from numerous interested people, including many intelligent-design supporters. Aside from a couple of unpleasant “You’re going to burn in Hell” e-mails from the fringe, the exchanges were respectful, interesting, and informative, from a broad spectrum of beliefs. Notice that these are not the leaders of the “intelligent design movement”, but mostly-Pennsylvanian newspaper readers responding to a column. Two observations are:

1. None of the “intelligent design” supporters seemed to seriously consider the possibility that the “intelligent designer” was a flying spaghetti monster or a space alien; where it could be determined, the correspondent identified the “intelligent designer” as God as worshipped in the Judeo-Christian tradition, and the correspondent came from a fundamentalist, conservative, or traditional Christian background.
2. None of the “intelligent design” supporters seem to have come to their religious beliefs based on the perceived difficulty of evolutionary biochemists in explaining blood clotting, flagella, or eyes. Awe and reverence for the glory of nature did seem to figure in some religious beliefs, but supposedly irreducibly complex items were not at the forefront.

This leads to some additional, important points. The broad umbrella of “intelligent design” allows an old Earth and allows evolution to have occurred, except at those moments when an unspecified intelligence tinkered with the process, so if you are a true sacred-book literalist, “intelligent design” may give you scant comfort. And many religious people object to “intelligent design” based on the argument that it is lousy theology—if an unspecified “intelligent designer” is introduced to high-school biology students based on a claimed difficulty that scientists are having in explaining intermediate steps in blood clotting, might future success in explaining blood clotting raise questions in the minds of those students about the validity of belief in the “intelligent designer”? The pastors at the author’s church seemed remarkably uninterested in getting high school biology teachers to take over religious instruction based on explanations of flagella.

Question: But shouldn’t we be fair, teach both sides, and let kids decide?

Answer: This is a hard one because we so strongly believe in fairness and in hearing a diversity of ideas. But, if you present “both sides” in science class, it isn’t science class anymore. Science is the human search for ways to make accurate predictions, and that means setting aside the ideas that don’t work (the Earth is flat, the Earth is the center of the universe) and keeping the ones that do. Teaching the controversy over evolution in science class would be akin to teaching the controversy over whether the Earth or the Sun is more nearly the center of the solar system.

Consider the scientific controversy over gravity. We don’t have a complete understanding of gravity yet. The grand unified theories of physics have not succeeded in explaining the quantum world and gravity through one set of equations, and other research frontiers await. But we have a pretty good idea that if you knock your pencil off your desk, the pencil will fall down. In the same way, there are lots of evolutionary questions, things we don’t know, and fascinating research frontiers, but the basic idea that kids are mostly like parents, differences affect success, and this leads to evolution, is very well established with very little uncertainty.

Discussions about “intelligent design” surely can be included in school—a school that does not recognize the reality of religion in the world is not preparing its students for that world. But “intelligent design” is not science, and the author believes that science classes should teach science.

Petrification - How is the Bone Turned to Stone?

In the photo above, the petrified crocodilian tooth (still sharp!) that Randall Irmis is showing to Irene Meglis in Petrified Forest National Park is subtly different from modern equivalents. Evolution remains the scientifically best way to explain observations such as these in the fossil record and to predict additional discoveries.

Credit: R. B. Alley © Penn State is licensed under CC BY-NC-SA 4.0

No magic is involved in the petrification of bone, wood, or other materials. The chemical environment inside organic materials is very different from the chemical environment outside. All groundwaters carry minerals, and when those mineral-carrying groundwaters encounter a change in chemical conditions, some chemicals usually are picked up while others are put down. Remember that water can poison people by picking up lead and other chemicals from old pipes, and that water can clog old pipes by putting down scum and hard-water deposits—picking up some chemicals and putting down others is the usual behavior for water. Water softeners work by pulling calcium out of the water and putting sodium back in.

When organic material is buried in mud, if enough adding and subtracting of chemicals occurs before the material is eaten by worms or fungi or bacteria, then the organic material can be “turned to stone”. This petrification is rare—most organics are recycled—but occurs often enough to give us plenty of fossils to study.

For example, silica is very common and is relatively insoluble in acidic solutions but very soluble in basic solutions. Groundwater in dry environments often is basic and so carries much silica. When this silica-carrying groundwater meets the organic acids in a buried tree or bone or other formerly living things, the silica may precipitate. Actual chemical processes are typically a little more complicated than explained here, but the principle is the same. Materials scientists are even succeeding now in using wood as a template for “growing” ceramics, replacing the wood with zeolites, silicon carbide, or other materials to make useful things by human-accelerated petrification.

Extinction and Absorbing Boundaries

If you go to a casino to gamble, you are likely to lose. This is partly because the games are stacked against you—the odds on all casino games favor the house. (The odds on state lotteries typically are even more in favor of the house, by the way.)

But, you also lose at a casino because you are poor and the casino is rich. Suppose that you start off with $10 and the casino starts off with $999,990. Together, you have $1,000,000. Suppose further that this is a bizarre casino with a perfectly fair game—you and the casino are equally likely to win. If you win $10, then you have $20 and the casino has $999,980. But, there is a slight catch—if you lose $10, you are at $0 and the casino will show you the door. If you stay and gamble for a while, the outcome is almost guaranteed; you will hit $0 before the casino does, the casino will have all of your money, and you will go home broke. The $0 mark is an absorbing boundary—you can’t bounce off of it (the casino won’t give you your money back), nor can you go negative and then return (well, you might go take out a loan, but your ability to get loans to cover gambling losses is much smaller than the casino’s ability to get loans, so you’ll eventually reach the point of no return—your money will have been absorbed by the casino).

Extinction works the same way. Once a species is gone, it is gone. You can’t have a negative number of tigers and then later have a positive number. So random fluctuations eventually kill off species. But, at certain times, such as when the meteorite hit at the end of the Mesozoic, or now as we humans spread across the surface of the planet and squeeze others out (more on this coming soon!), extinctions go a whole lot faster than normal.

Just for your interest, here are a couple of thoughts on Extinction, from Aldo Leopold’s A Sand County Almanac. Some of the Almanac is written in ways that seem outdated now, including its non-neutral use of gender.  But, it was ahead of its time in 1948, when Leopold made these remarks at the dedication of a monument to the last passenger pigeon, after humans drove that highly abundant species to extinction.  We will return to biodiversity in the next Module, so this may give you useful things to think about heading into Module 12.  

It is a century now since Darwin gave us the first glimpse of the origin of the species. We know now what was unknown to all the preceding caravan of generations: that men are only fellow voyagers with other creatures in the odyssey of evolution. This new knowledge should have given us, by this time, a sense of kinship with fellow creatures; a wish to live and let live; a sense of wonder over the magnitude and duration of the biotic enterprise. 
-Leopold, Aldo [7]: A Sand County Almanac, and Sketches Here and There, 1948, Oxford University Press, New York, 1987 

For one species to mourn the death of another is a new thing under the sun. The Cro- Magnon who slew the last mammoth thought only of steaks. The sportsman who shot the last pigeon thought only of his prowess. The sailor who clubbed the last auk thought of nothing at all. But we, who have lost our pigeons, mourn the loss. Had the funeral been ours, the pigeons would hardly have mourned us. In this fact, rather than in Mr. DuPont's nylons or Mr. Vannevar Bush's bombs, lies objective evidence of our superiority over the beasts. 
-Leopold, Aldo [7]: A Sand County Almanac, and Sketches Here and There, 1948, Oxford University Press, New York, 1987 

Optional Enrichment Article #2

“Intelligent Design” Newspaper Editorial by Dr. Alley

Column by R.B. Alley, published in Harrisburg Patriot-News (2004) and republished in
Pittsburgh Post-Gazette and Centre Daily Times early in 2005.

The School Board of the Dover (PA) Area School District (November 2004) mandated the teaching of so-called “intelligent design” alongside Darwinian evolution in science classes, and similar actions are at least being considered elsewhere. As a religious person and a scientist, I hope that school boards will avoid mixing apples and angels in the classroom.

Like many scientists, I am fortunate to teach. We know that our students will soon discover things we missed, often correcting our mistakes in the process. Thus, a scientist would be foolish to claim that science gives absolute knowledge of Truth. If I successfully predict the outcome of an experiment, I’m never sure whether my understanding of the world is True, whether I’m pretty close but not quite right, or whether I’m really confused and was just lucky this time.

But, our society has agreed to act as if science is at least close to being true about some things, and this makes us very successful in doing those things. Carefully crafted bits of silicon really are computers, airplanes designed on those computers using principles of physics really do fly, and medicines from biological laboratories really do cure diseases. The military has investigated psychics as well as physicists but continues to rely on the physicists because they are so much more successful. Science, tightly wedded to engineering and technology, really does work, and is the best way we humans have invented to learn to do many things.

Science asks a high price for the value it gives, however, and that price is a real dedication to science. The cartoonist Sidney Harris once drew a panel showing two long strings of blackboard equations connected by “Then a miracle occurs,” with one scientific-looking character saying to the other “I think you should be more explicit here in step two.” For a plane to fly, for a medicine to cure disease, every step must be tested, and everyone else must be able to follow those steps. Science students are welcome to rely on divine inspiration, but they cannot rely on divine intervention in their experiments. Scientists, like athletes, must follow the rules of the game while they’re playing.

What, then, are the rules? First, scientists search for new ideas, by talking to people, or exploring traditional knowledge, or in the library or other places. We look for an idea that explains what we see around us, but that also disagrees with an old idea by predicting different outcomes of experiments or observations. Then we test the new idea against the old one by doing experiments or making observations. An idea that repeatedly makes better predictions is kept; an idea that repeatedly does more poorly is set aside. An idea that can’t be tested also is set aside; it isn’t scientific. Even if I really love an idea, or really believe it is True, but I can’t think how to give it a fair test, I have to set it aside for now. Some people find this limiting and avoid science; others find it exhilarating and are drawn to science. Doing this well gives us good things from good science.

Who decides what is or isn’t science? Scientists—with other thinkers watching over our shoulders—do the day-to-day deciding, but ultimately the whole bill-paying, newspaper-reading community is checking on us to make sure we are producing useful insights.

Does science have limits? Will we run out of new ideas? Will we hit problems that we can’t solve? Perhaps. But when I come out of a classroom of bright young students, I am convinced that we’re nowhere near any limits that might exist and that there is still much to discover.

So, what about Intelligent Design, or even Young-Earth Creationism, and teaching them in science class? They’re interesting ideas. But, some parts we don’t know how to test. Even if they are said by scientists, they aren’t science. And the testable parts have been tested and found wanting—they don’t do as well as the “scientific” view in explaining what we see around us, or in predicting what we find as we collect new tree-ring records and ice-core samples, or as we search for oil and valuable minerals, or as we watch dangerous new diseases appear faster than our bodies can respond to them. We spend a few hours discussing the main pieces of evidence in class, and a lifetime isn’t enough to cover all the details, but scientists have been working on these questions for centuries and have a pretty good idea of what works now. Evolution “in the dark backward and abysm of time” is a scientific theory, not Truth, but it is very good science.

How does this fit into the bigger picture? Although some people are happy to view science as merely a tool, others do believe that the remarkable success of science means that we are getting closer to the truth. But even these people disagree about that truth: a mechanistic universe, a benevolent and omnipotent deity, or something else? Fascinating as they are, such questions are for now outside of science. Many scientists and religious people are thinking about such questions, but no experimenter knows how to guarantee the cooperation of an omnipotent deity.

By all means, students should ask deep questions, think and discuss, and probe. Science does not tell us what we ought to do, and students will have to join us in addressing what ought to be as well as what is. But if we want to face the big questions with better medicines, with computers that function and planes that fly, with clean water and buildings that don’t fall down, I believe that we should teach science in science class.

A Rocking Review

Here’s a “musical” summary of evolution, illustrated with Alley cats, and set to an old tune.

Video: Evolution Marches On (03:31 minutes)

Module 11 Wrap-Up

Review Module Requirements

You have reached the end of Module 11! Double-check the list of requirements on the Welcome to Module 11 page and the Course Calendar to be sure you have completed all the activities required for this module.

Supplemental Materials

Following are some supplementary materials for Module 11. While you are not required to review these, you may find them interesting and helpful in preparing for the quiz!

• Website: Florissant Fossil Beds National Monument
• Website: Dinosaur National Monument

Comments or Questions?

If you have any questions, send an email via Canvas, to ALL the Teachers and TAs. To do this, add each teacher individually in the “To” line of your email. By adding all the teachers, the TAs will be included. Failure to email ALL the teachers may result in a delayed or missed response. For detailed directions on how to do this, see How to send an email in GEOSC 10 in the Important Information module.