No. 119: Sep-Oct 1998
Geologists usually don't bother looking for oil in very ancient (Precambrian) rocks for two reasons:
Yet, Precambrian oil in commercial quantities has been found in formations up to 2 billion years old (in Siberia, Australia, Michigan, for example). While some of this oil might have migrated in-to the Precambrian rocks from younger source rocks, some of it does seem indigenous and, therefore, ancient.
Now, three Australian scientists (R. Buick, B. Rasmussen, B. Krapez) have discovered tiny nodules of bitumen (lumps of hydrocarbons) in sedimentary rocks up to 3.5 billion years old in Africa and Australia. These bitumen nodules were formed when natural hydrocarbons were irradiated by radioactive isotopes that coexisted in the ancient rocks. Futhermore, these African and Australian rock formations were never severely deformed or subjected to high temperatures. The possibility exists, therefore, that some of the earth's oldest rocks may contain substantial oil reserves. So far, no one has seriously looked for oil in Precambrian rocks because of the two preconceptions noted above.
(Palmer, Douglas; "Any Old Oil?" New Scientist, p.22, March 14, 1998.)
Comments. Large quantities of oil and bitumen 3.5 billion years old have profound implications. Far from being lifeless, the most ancient of our planet's seas may have been thick soups of bacteria and other simple life forms. So much terrestrial life so soon after the formation of the earth could imply that there was an extraterrestrial inoculation of biotic material that gave terrestrial life a jump start -- assuming that this ancient oil and bitumen are truly biogenic! The possible (and highly anomalous) abiotic origin of oil and natural gas are covered in some depth in Anomalies in Geology.