PrintModule 3 Overview
Each spring, plants grow rapidly on the land and in the ocean. And, each year, enough plants die to approximately balance the new growth. Most of the dead plants are broken down quickly, by bacteria or bison or button mushrooms, or any of the other living things that rely on plants, or by being burned in fires. But, some of the plants are buried without oxygen, and begin the process of being cooked by the Earth to make fossil fuels.
Woody plants eventually may become coal, “slimy” plants may become oil, and both produce natural gas. The fossil fuels now in the Earth accumulated over a few hundred million years. If we keep burning them at modern rates, the fuels will be gone in a few hundred years; if much of the world continues to catch up with the US rate of use, the fossil fuels may become quite scarce late in this century. Nature will make more, but not enough to be helpful until millions of years have passed.
Video: Colyer Lake (4:11)
DR. RICHARD ALLEY: This lake used to be a lot bigger than it is now. People dammed a little stream to make the lake, but the dam is not considered safe anymore. And so they've lowered the water level. It's going to let us see some of the things that happen under a lake. And so we're going to go for a little trip here to find out how fossil fuels are made.
So the rivers wash mud, sand, gravel, silk, clay all sorts of sizes into lakes and the small pieces are washed away wherever there's a strong current, and they settle where there's no current. And in those places, they settle with a lot of dead plants that have lived above them. And those dead plants will start to break down in the mud. And bacteria will use them, and those bacteria make methane. And so you already start to see bubbles coming out of the mud here. That actually is the first step in making fossil fuels. This is the bacteria making methane, but later they heat of the Earth will make methane.
So if you take mud like this, and you buried it with more mud, and then more mud, and then more mud, and then starts being heated by the heat of the earth, but that organic matter down in there will start making oil to go with the methane, the natural gas that we see coming off of here. Lots of dead plants wash into water, and these are woody ones. And so this is a kind of thing that could make coal. In addition, lots more plants live in the water and the slimy plants, algae, cyanobacteria, and they eventually give rise to oil, and both give rise to natural gas.
So sometime way back in geologic history, there was a nice ocean-- warm, not a lot of oxygen in the water because it was warm-- lots of plants growing at the surface, but that oxygen bubbles out to space. And then the dead plants and mud settle to the bottom in layers. And those layers can become thousands of feet thick. Worms try to eat the dead plants that are falling down, but when they run out of oxygen, a lot of the dead plants are buried. And then as the heat of the earth cooks them, they make oil and gas.
A lot of oil and gas actually generate high pressure, and they make cracks. And they seep out of those cracks from the rock that they're-- which is now called shale-- and then they either bubble up through the water, all the way to the surface to make an oil seep or a gas seep. Or they get caught somewhere on the way in special geologic places that we can drill into to get the oil and gas.
A lot of the organic matter is still left in the rock. This is a sort of black looking rock because it's still full of organic matter. And what we're learning to do now is to break up the hard rock, like this, to make it more like this loose stuff. And they do so by drilling through it, not with a chisel, but with a real serious drill. Pumping fluid in at very high pressure to break the rock. It's called fracking, and then the oil and gas can go all to those little cracks and you can pump them out and use them.
Credit: Dutton Institute. "EARTH 104 Module 3 Colyer Lake." YouTube. July 1, 2013.