Under extreme heat and pressure, the remains of lush, swampy forests can eventually become coal.

350 to 290 million years ago, coal forests thrived in lowlands at the edges of rivers and seas (like today's Louisiana bayous). Tropical climates encouraged dense growth of ferns, tree ferns, and club-mosses.

Carbon is present in plant tissue. In some places, thick masses of dead plants accumulate in water. Eventually, after long periods of deep burial, that carbon can be compressed into coal.

Other fossil fuels, such as oil and gas, can form from the remains of millions of tiny marine organisms.

Formation of Coal

Peat is partly decayed plant material found in bogs and swamps. It accumulates as dead plants are pressed into a porous mat.
Lignite forms as accumulated rock layers and sediments press peat into a soft coal-like material.
Bituminous coal results when heat and pressure transform lignite into soft coal.
Anthracite coal forms from bituminous coal that has undergone extreme heat and pressure to become very hard.