Introduction
Have you ever seen dinosaur fossils at a museum? If so, you may have read about how the
dinosaur bones turned into fossils. The same processes that formed these fossils also formed
some of our most important energy resources. These resources are called fossil fuels. Fossil
fuels provide a very high quality energy, but because of our demand for energy, we are using
up these resources much faster than they formed.
Formation of Fossil Fuels
As you might guess from their name, fossil fuels are made from fossils. Fossil fuels come
from materials that began forming about 500 million years ago. As plants and animals died,
their remains settled on the ground and at the bottom of bodies of water. Over time, these
remains formed layer after layer. Eventually, all of these layers were buried deep enough
that they were under an enormous mass of earth. The weight of the earth pressing down on
these layers created intense heat and pressure.
After millions of years of heat and pressure, the material in these layers turned into chemicals
calledhydrocarbons,which are compounds of carbon and hydrogen. The hydrocarbons in
these layers are what we call fossil fuels. The hydrocarbons could be solid, liquid, or gaseous.
The solid form is what we know as coal. The liquid form is petroleum, or crude oil. We call
the gaseous hydrocarbons natural gas.
You may be surprised to learn that anything that used to be alive could change enough to
become something so different, such as coal or oil. There is enough heat and pressure deep
below the earth’s surface even to create diamonds, which are the hardest natural material
in the world.
Like fossil fuels, diamond is made of carbon. In fact, diamond is a type of pure carbon, so it
does not contain the hydrogen that fossil fuels do. What determines whether the remains of
living things deep in the earth turn into coal, oil, natural gas, diamond, or something else?
All of these materials form under high heat and pressure, but the conditions are different for
each material.
Coal
Coal is the solid fossil fuel that forms from dead plants that settled at the bottom of swamps
millions of years ago. The water and mud in the swamps affected how the remains of plants
broke down as they were compressed. The water and mud in the swamp keep oxygen away
from the plant material. When plants are buried without oxygen, the organic material can
be preserved or fossilized. Then, other material, such as sand and clay, settles on top of
the decaying plants and squeezes out the water and some other substances. Over time, the
pressure removes most of the material other than carbon, and the carbon-containing material