What is the age of the earth's oil?

Question

Oil in the ground is found under the oceans and seas. It is made of dead fish. But from what period are those fish? I heard they are about 119 million years old. But fish exist much longer than that. So is it clear how old our oil is?

Answer 1

Fish have little to do with oil formation. You need a much more significant source of organic material to produce enough hydrocarbons to be significantly viable economically.

Actually, any organic material can be a source of some amount of hydrocarbon formation, but the most viable source is from zooplankton, the tiny little organisms which live in the upper levels of the ocean. When they die, their bodies fall very very slowly to the ocean floor. Ever watched a speck of dust float in the air and noticed how long it would take to land? Now just imagine that speck of dust trying to get to the ocean floor amidst swimming fish, plants, and ocean currents. When the zooplankton bodies finally reach the floor and can accumulate enough for significant deposition, the material can be converted naturally into oil and gas.

The area of the ocean and the zooplankton's short life cycle means that there is a lot of material, though it needs significant time to actual form.

The oldest oil was formed in the Eocambrian siltstone in Oman, way before any fish were said to have evolved. Oil can also be found all the way up through the Mesozoic and Cenozoic eras. In any case, oil is formed from invertebrate organisms, so neither fish, nor dinosaurs, have little to do with oil, contrary to popular belief.