How Coal Is Formed


Based on the diagram “How Coal Is Formed

Dinosaurs are old. But you know what’s even older? Coal!

The coal that we use today began to form around 300 million years ago. Did you know that coal comes from plants? Back before the dinosaurs, a lot of the Earth was covered in swamps and bogs. Special types of plants that don’t exist anymore lived in these areas. When those plants died, the stems and leaves would sink to the bottom of the swamps.

Layers and layers of these dead plants gathered under the water. They then turned into peat, a soggy, sponge-like material that is sometimes used for gardening today.

As time passed, the swamps and bogs started to dry up. The peat was left behind and got buried by sand, clay, and other materials. As the peat was buried further and further underground, it was exposed to both pressure and heat. After millions of years, the peat changed—into coal!

Types of Coal

There are four different types of coal: lignite, subbituminous, bituminous, and anthracite.

Lignite is soft coal, and is sometimes brown instead of black. You can sometimes even see bits of plant still inside it. Lignite was exposed to the least amount of heat and pressure.


Subbituminous is medium-soft coal. It formed after lignite was exposed to more heat and more pressure.




Bituminous is medium-hard coal, and had even more heat and pressure around it.



Anthracite, the hardest coal, is a glossy black color. It was exposed to the most heat and the most pressure out of all of the coal types.



Where Can We Find Coal?

Since coal formed by being buried by other materials, coal miners have to go below the surface to find it now. Some mines are all the way underground. Miners have to take a special type of elevator to get there. Other mines move the soil and rocks to the side, making a big pit where they can get to the coal more easily. After miners remove all of the coal, the soil and rocks are replaced and the land is smooth again.

And guess what! More coal is still being formed today. Big swampy places—like the Florida Everglades—are very similar to the swamps that existed 300 million years ago. In the future, the Everglades might be a great place to find coal!


Be sure to see the accompanying lessons:
How Coal Is Formed
Field Testing Coal Samples

As well as the accompanying interactive diagram:
How Coal Is Formed

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