Underground fuels like oil, coal, and natural gas are collectively known as fossil fuels.

Here's why they are called fossil fuels:

* Formed from ancient organic matter: They were formed over millions of years from the remains of dead plants and animals (specifically, plankton and other marine organisms for oil and natural gas).

* Stored underground: These remains were buried under layers of sediment and, over time, heat and pressure transformed them into the fuels we use today.

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