Petroleum formation theories

fossil fuel, petroleum is believed by most scientists to be the transformed remains of long-dead organisms. The majority of petroleum is thought to come from the fossils of plants and tiny marine organisms. Larger animals might contribute to the mix as well.Another theory holds that more oil was in Earth from the beginning than what's been produced by dead animals, but that we have yet to tap it. n the leading theory, dead organic material accumulates on the bottom of oceans, riverbeds or swamps, mixing with mud and sand. Over time, more sediment piles on top, and the resulting heat and pressure transform the organic layer into a dark and waxy substance known as kerogen. Left alone, the kerogen molecules eventually crack, breaking up into shorter and lighter molecules composed almost solely of carbon and hydrogen atoms. Depending on how liquid or gaseous this mixture is, it will turn into either petroleum or natural gas. Scientists aren't really sure, but they figure it's probably on the order of hundreds of thousands of years. The idea that petroleum formed from dead organic matter is known as the "biogenic theory" of petroleum formation, and was first proposed by a Russian scientist almost 250 years ago. In the 1950s, however, a few Russian scientists began questioning this traditional view and proposed instead that petroleum could form naturally deep inside the Earth. This so-called "abiogenic" petroleum might seep upward through cracks formed by asteroid impacts to form underground pools, according to one hypothesis. Some geologists have suggested probing ancient impact craters in the search for oil. Abiogenic sources of oil have been found, but never in commercially profitable amounts. The controversy isn't over whether naturally forming oil reserves exist, said Larry Nation of the American Association of Petroleum Geologists. It's over how much they contribute to Earth's overall reserves and how much time and effort geologists should devote to seeking them out.