Where does oil come from?

This is pretty far away from astronomy, and I am not a geologist, but there is a book called 'Science and Earth History: the evolution/Creation controversy" by Arthur Strahler which discusses the scientific view, and why the Creationists literature on this subject is worse than being wrong.

There is general agreement in mainstream science that petroleum originated when organic matter in ancient muds and clays accumulated in subsiding geological basins. This sediment was heated over a period of millions of years as geological processes brought the material deeper underground. The end product depends on just how deep the organic-rich sediments were carried. At 150 - 200 C, natural gas is the end produce. At 60 - 150 C, oils are produced, and leach out of the rocks to form pockets that get trapped between impermeable layers of shale.

The geologic period when petroleum deposits can form depends on a balance between sufficient sources of organic material ( trees, plants etc with waxy 'hydrocarbon coatings') and the occurrence of the proper geologic subsidence and trapping processes. Deposits found in Precambrian rocks are rare, as are deposits in the much more recent Pleistocene 'rocks'. However, tar deposits are found in the latter rocks such as the famous 'La Brea Tar Pits' in southern California. It takes several million years for the petroleum products such as oil to migrate out of their parent rocks into the appropriate 'reservoir' rocks where they get trapped and accumulated into sub-surface pools. Radioactive dating of the rocks in which oil deposits occur span the range from the Cambrian Era to the Cretaceous Era between 65 million and 500 million years ago.

Creationists propose that these deposits were laid down by the Great Biblical Flood some few thousand years ago in 2350 B.C, when the organic deposits ( Flood victims) were entombed in the Earth. Their conversion into oil and gas deposits then took a few thousand years to the present time. So, everytime you fill up at the gas pump you are pouring liquified dead humans and ancient creatures into your car.

Swell.

What is the chief evidence that disputes the Creationist proposal? The migration of petroleum from their strata of origin into surrounding rocks takes a long time, measured in millions of years, not centuries. This is based on the physics of fluid flow through semi-permeable material under a pressure gradient. There is nothing speculative about this mechanism, anymore than there is controversy over how water flows through a garden hose. There is also the problem of the time scale for conversion 'or cracking' of organic matter into oil and gas derivatives under the rather gentle temperature and pressure conditions found in nature. Again this is a matter of organic chemistry, not speculation, and the time scales are again measured in millions of years not days or centuries.


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