Where oil comes from

I have long believed (and still believe) that oil comes from dead life (hence "fossil fuel"). As explained in Wikipedia:

All oils, with their high carbon and hydrogen content, can be traced back to organic sources. Mineral oils, found in porous rocks underground, are no exception, as they were originally the organic material, such as dead plankton, accumulated on the seafloor in geologically ancient times.

But now here's the latest from Titan:

According to new Cassini data, Saturns largest moon, Titan, has "hundreds" times more liquid hydrocarbons than all the liquid fossil fuel deposits on Earth. This is impressive as Titan's 5150 km diameter is only about 50% larger than Earth's Moon and only a little larger than the planet Mercury. Titan's hydrocarbons cycle into the atmosphere, fall as rain and collect in lakes creating massive lakes and dunes.

Titan is a planet-sized hydrocarbon factory. Instead of water, vast quantities of organic chemicals rain down on the moon's surface, pooling in huge reservoirs of liquid methane and ethane. Solid carbon-based molecules are also present in the dune region around the equator, dwarfing Earth's total coal supplies. Carl Sagan coined the term "tholins" to describe prebiotic chemicals, and the dunes of Titan are expected to be teeming with them.

This may all be entirely what the experts expected, but it does suggest the question: if Titan is full of this stuff and never had life, then is it possible that at least some of Earth's oil and gas are not from dead life after all? As it happens, years ago I came across a theory - evidently not widely accepted to this day, presumably for good reason - that Earth's oils do not, in fact, come from dead life.

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I think the evidence is too

I think the evidence is too strong that biotic matter was behind atlest some of the fossil fuels on Earth, but theoretically it is possible that the molecular structure and chemical properties of fossil fuels can be replicated without life having existed at one point. Basically, both theories could in theory be right.

apples and oranges

Titan has naturally occurring simple hydrocarbons, like methane and ethane. The fossil fuels on Earth have a substantially more complex structure that is unlikely to form without life. Furthermore, oil and gas companies employ geologists who successfully use biological markers to identify potential new sites of underground deposits.

In the mid 20th century, there was a competing theory about how fossil fuels might form through purely geologic action. However, since then it's been completely debunked. See Abiogenic origin of hydrocarbons: an historical overview


The fossil fuels on Earth have a substantially more complex structure that is unlikely to form without life.

I expected there was some good reason for rejecting the hypothesis. However, the argument from complexity obviously does not apply to Earth's methane.

oil and gas companies employ geologists who successfully use biological markers

That might apply to methane.

Making complex hydrocarbons is fairly easy.

Making complex hydrocarbons is fairly easy. The processes on Titan are probably somewhat different, due to the different temperature range, but on, or more importantly, in, the Earth, the process is something like this:

  1. If you heat almost *any* carbon-containing substance in the presence of water, you get "water gas", which is a mix of Hydrogen and carbon monoxide. (done artificially, this is called Syngas) This can occur with any buried organic material, or primordial carbon in the Earth's crust.
  2. If the water-gas encounters iron oxide in the rock as it seeps upward through the crust, and does so in a certain range of temperature and pressure, you get petroleum. (done artificially this is called the Fisher-Tropsch process) And yes, this does yield the more complex hydrocarbons.

So, formation of petroleum from primordial carbon is not impossible, or even unlikely. However, you can do isotopic analysis of the petroleum to figure out where the carbon in it came from, and from what I've heard, the results so far are more consistent with buried biological material being the source. (Living cells have preferential uptakes of certain isotopes, and thus give something of a 'fingerprint' ) Advocates of abiogenic theories of petroleum origin suggest that the isotope fingerprints are artifacts due to the actions of microbes in the Earth's crust on the petroleum (the "deep hot biosphere"), but that seems like a stretch.


I'm going with what MD said plus ...

The reason this idea is being pushed by some is to argue that petroleum is much more abundant than we think. The claim being that some deep inorganic process is backing a large inflow of petroleum.

I don't buy it. Even if the petroleum were produced by inorganic means we would still be as much in the dark about how it percolates up and pools. Still seems that these pools were formed over millions of years.

The processes by which organic matter is pumped into the mantle by subduction zones already seems to result in a process of slow percolation up from very great depths. I don't see how would be significantly different from an inorganic process. You'd think that both processes would have settled down to a steady state hundreds of millions of years ago. Actually an inorganic one should have reached steady state more than a billion years ago.

If lots of oil were refilling the reserves at a rate comparable to what we are pumping out now one would kind of expect that the oil fields would have overflowed to the surface long ago. We should be able to find oil fields because of the vast lakes of oil above them.

Seems more likely to me that there are relatively tiny inflows into these oil fields. They may be backed up very deep but they still reflect tens of millions of years of accumulation.

Even if petroleum is more

Even if petroleum is more abundant than we think, it is important to move towards alternate sources due to economic and environmental concerns.