The popular idea that oil, gas, and coal are made of dead dinosaurs is mistaken. Fossil fuels consist mainly of dead plants – coal from trees, and natural gas and oil from algae, a kind of water plant. Your car engine doesn’t burn dead dinosaurs – it burns dead algae.
Oil, gas, and coal deposits are really remnants of ancient muddy swamps. Dead plants accumulate, and, over time, pressure turns the mud and dead plants into rock. Geologists call the once-living matter in the rock kerogen. Earth’s internal heat cooks the kerogen. The hotter it gets, the faster it becomes oil, gas, or coal. If the heat continues for long enough after oil forms, all the oil might become gas. The oil and gas then creeps through cracks in the rocks. Much is lost. We find oil and gas today because some happened to become trapped in porous, sponge-like rock layers capped by non-porous rocks. Fossil fuel experts call this arrangement a reservoir.
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