300 million years ago in the Carboniferous Period, soaring trees, giant tree ferns, and other leafy plants grew in steamy swamps near the equator. Over time, the plants fell into stagnant water, decomposed, and were preserved as peat—and eventually became coal.
In the ocean, the remains of tiny plants and animals collected on the seafloor and were buried by layers of sand and rock. Under pressure, the remains decomposed, underwent chemical changes, and formed the natural gas and petroleum deposits we use today.
Fossil fuels took hundreds of millions of years to form, and they are not a renewable resource.
Alternative, renewable sources of energy are increasingly in use as technology improves to generate electricity from the sun, wind, waves, and geothermal sources. But we continue to depend on fossil fuels for the majority of our energy needs.