Download Check for Understanding: Objective 2 ANSWER KEY

Check for Understanding: Objective 2
Formation of Fossil Fuels
1. Describe the process that leads to the formation of fossil fuels.
2. Explain how the formation of coal is different than the formation of petroleum and
natural gas.
3. Draw a diagram showing where:
a. Petroleum (oil) forms
b. Natural gas forms
Check for Understanding: Objective 2 ANSWER KEY
Formation of Fossil Fuels
1. Describe the process that leads to the formation of fossil fuels.
Fossil fuels formed from prehistoric plants and animals that lived hundreds of millions of years ago. As
organisms died, they sank to the bottom of the swamps of oceans. They formed layers of a spongy material
called peat. Because no oxygen was present, organisms did not entirely decompose. Over many hundreds of
years, the peat was covered by sand and clay and other minerals, which turned into a type of rock called
sedimentary. More and more rock piled on top of more rock, and it weighed more and more. It began to press
down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over
millions of years, it turned into fossil fuels.
2. Explain how the formation of coal is different than the formation of petroleum and
natural gas.
Coal formed from the dead remains of trees, ferns and other plants that lived 300 to 400 million years ago.
In some areas, such as portions of what-is-now the eastern United States, coal was formed from swamps
covered by sea water. The sea water contained a large amount of sulfur, and as the seas dried up, the sulfur
was left behind in the coal.
Oil and natural gas formed from organisms that lived in the water and were buried under ocean or river
sediments. Heat and pressure combined to compress and "cook" the organic material under layers of silt. In
most areas, a thick liquid called oil formed first, but in deeper, hot regions underground, the cooking process
continued until natural gas was formed. Over time, some of this oil and natural gas began working its way
upward through the earth's crust until they ran into rock formations called "caprocks" that are dense enough
to prevent them from seeping to the surface. It is from under these caprocks that most oil and natural gas is
produced today.
3. Draw a diagram showing where:
a. Petroleum (oil) forms
b. Natural gas forms