Everyday Uses of Rocks and Minerals - Shelf 12
When we describe oil and coal as fossil fuels, we mean it: they are produced by the cooking of decomposed plant and animal matter deep in the earth's crust over many millions of years. Fossil fuels are a form of solar power: they are energy from the sun trapped by plants millions of years ago. Oil is formed in oil shales, but once it becomes liquid it tends to rise until it is trapped in a porous reservoir rock, like the ones shown here. Drilling into the reservoirs releases the oil for human use. Finding oil is a tricky proposition, combining the science of geology with the art of imagining where the oil would flow within the crust.