Fossil Fuels---Investigation 3 Energy Resources
Vocabulary terms:
Coal
Petroleum
Swamp
Peat
Natural gas
Figure 1: Sketch of an ancient coal swamp.
Lignite
Bituminous coal
Organic Matter
Seal
Anthracite coal
Reservoir
Coal Swamps
Coal is formed from the growth of a lot of trees in swamps.
Swamps are low areas where the ground is almost constantly covered
with water. As these trees died, more trees grew on top of them. The
trees kept dying and growing on top of each other, and thick layers of
dead trees built up under the water. Coal swamps are rare today, but
used to be common in the Earth’s past. The weather conditions on Earth
change over time, so a coal swamp eventually became covered with mud
and sand. This is why you will find coal layers in between other rock
layers.
Types of Coal Materials
Before the dead trees are buried under the water, they are in the form of peat.
Peat is a spongy material that is made up of plant materials that are decomposing.
When the peat is buried, it is packed together by the weight of the material from
above. The water that was buried with the peat is squeezed out. Heat is also added as
the peat gets buried deeper. This heat causes a chemical change in the peat, and the
peat starts to break down. Gases are squeezed out as the peat changes form.
As the peat is buried and heated, it eventually becomes solid coal. The more it
is buried and heated, the more it chemically changes. It has more carbon atoms and
less other atoms in it. The stages of
coal are: peat, lignite, bituminous coal,
and anthracite coal (Figure 2).
Bituminous coal and anthracite coal
are deep in the Earth. To get these
types of coal, you have to dig deep
mines. Lignite is closer to the surface,
Figure 2
and can sometimes be mined directly
on the surface when erosion has taken away the
dirt on top of the lignite.
Figure 3: How plants change to peat, lignite,
and then coal.
Where Coal is Found in the United States
Figure 4
In the United States, you can find coal in many places (see Figure 4).. The Appalachian Mountains in
the eastern United States contains most of the bituminous coal and almost all of the anthracite coal. This is
where you find deep coal mines. You can also find coal in most of Illinois and Missouri. This coal can be
surface mined. Lignite is found in the western United States. This is also surface mined.
Petroleum (oil) and Natural Gas Formation
Petroleum, also called crude oil, is a liquid made
up of a mixture of carbon and hydrogen atoms. Natural
gas is also made up of carbon and hydrogen atoms. Both
petroleum and natural gas are formed deep in the Earth
over a long period of time.
Figure 5: Examples of the tiny sea plants
and animals that die and eventually make
up oil.
Much of the ocean floor is covered with muddy
sediments. In some places, these sediments contain a lot
of organic matter. This organic matter is made up of tiny
dead sea plants and sea animals (see Figure 5). These
tiny plants and animals live at the surface of the ocean,
but sink to the bottom when they die. They are then
buried by sediment. As more and more sediment is layered on the ocean floor, the organic matter is buried
deeper and deeper. As it gets buried deeper, the temperature rises from all the pressure on the organic
matter. If the temperature increases in just the right way, the organic matter is changed into gas and oil.
Petroleum and Natural Gas Reservoirs
When the oil and gas are first created, they are just tiny drops
or bubbles in the rock. These tiny drops rise upwards because they
are less dense than water. Think about how it looks when you mix oil
and water. Oil always floats on top. These droplets keep on rising
until they get stuck under a thick rock layer that they cannot move
through. This layer of rock is called a seal (see Figure 6). When we
drill for oil and gas, we drill through this seal to pump out the oil or
gas. This rock that contains the oil or gas underneath is known as a
reservoir.
Figure 6. See how the oil and gas form
and then move (migrate) upwards until
they reach the seal (non-porous rock).
Porous means to have holes.