Petroleum is thought to have originated mainly from the remains of sediments of photosynthetic organisms which sedimented from ancient seas, and were heated and compressed by geological processes. Assuming that to be true, it is interesting to note that photosynthetic organisms originated almost 3.5 billion years ago.
The higher the oxygen level the higher the rate of sedimentation of photosynthetic organisms, presumably. Note that such sedimentation began to occur nearly 3 gya. Also note that the vast majority of petroleum which humans have begun to tap into, originated roughly 100 mya or more recently. I think you will agree with me that the Proterozoic Era (2.5 gya to about 540 gya) is likely to have been extremely prolific in the sense of laying down organic carbon in sediments.
Now, observe the Tethys Sea in the image (see Tethys Ocean). The Tethys Sea (Ocean) opened about 250 mya and closed about 10 mya. Most of the modern world's known oil and gas reserves lie in the sediments which once underlay the Tethys water masses. Much of this oil and gas is of fairly recent origin, geologically speaking, although some dates back to the early Triassic (250 to 200 mya). It only takes a hundred thousand years or so to make petroleum by natural means, depending upon local geology.
Now, I know you are saying to your computers, "But Al, if we are only beginning to tap a very small fraction of all the oil that has been deposited, where is all the rest of the oil?"
To which I reply, "Where do you think it is? Floating beyond the orbit of Pluto?" No, seriously, a lot of things can happen to oil deposits over time. Some can seep into oceans and be eaten by microbes. Some can be turned into various types of gas, and escape or be adsorbed by minerals. But most of it is likely to have been buried in the constant geologic upheaval of the planet's layers of rock.
The Japanese and Chinese have recently begun finding significant deposits of oil and gas within volcanic rock. Oil geologists are beginning to look beneath undersea volcanic deposits for submerged oil fields of great potential. The Russians have been finding significant petroleum beneath deep igneous and metamorphic layers for many years. The history of oil formation goes back over ten times farther than almost all of the oil humans have retrieved or located so far -- although drops of bitumen has been found in rocks dated between 2.6 and 3.2 gya.
Australian expert in petroleum geology, Associate Professor Colin Ward of the University of New South Wales, says it's not surprising that algae and other simple life forms existed during this early stage of the Earth's history.
What is significant, is that there are now signs they were producing oil.
"He's found good evidence that the processes that generate oil were active in a very early history," he says.
Rasmussen's discovery may have implications for exploration, Ward says.
"It focuses attention back on very old rocks as a possible places to look for more oil and gases," he says. _Source
So why do I say that the age of oil may be ending soon? Because while it takes 100,000 years (plus or minus) to make petroleum by natural processes, it only takes a matter of weeks -- from start of algae crop to harvesting and processing -- using modern methods. Yes, modern oil made this way is very expensive, but that is because we have just begun learning to create it. Within 20 years, Al Fin energy experts assure me that microbial fuels and energy will be fully price-competitive with petroleum, and rapidly scaling to match production within 30 years.
You may hear a lot of talk about "peak oil" in certain circles. The most likely kinds of peak oil you will see are "political peak oil" from bad energy policy or political conflict, and "peak demand" -- when consumers choose other forms of energy and fuel than petroleum. Peak demand can also occur from economic, or other forms of collapse, which we hope does not occur.
The beginning of oil, the end of oil. Mayhaps both.
More 9Nov10: Whether crude oil survives or is decomposed to wet and / or dry natural gas probably depends more upon the catalytic environment in the reservoir than the temperature. The presence of mineral catalysts changes the decomposition picture significantly. We may discover that much of the sub-seafloor methane clathrate resource is a result of this type of natural catalysis of crude oil to natural gas, which migrates upward to a cooler, moister environment and is captured in clathrate. Of course, abiotic gas might well do the same thing in some formations.
By. Al Fin