PDA

View Full Version : Abiotic Hydrocarbons



cjackson
2014-Sep-07, 09:42 PM
How do planets and moons with no life have large amounts of methane and other hydrocarbons? Is it possible that oil and coal can form without life? If so, how?

Noclevername
2014-Sep-07, 10:01 PM
IIRC hydrocarbons form in deep space, we have found them in nebulas and the coronas of new stars.

Swift
2014-Sep-07, 11:43 PM
Here (wikipedia) (http://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules) is an extensive list of molecules found in space, including methane.

I cannot image circumstances where coal and oil form without life, they are much too complex. But simple organics, like methane, are relatively easy, given enough energy, and the UV from a star, or lightening on the surface of a planet, would be enough.

Here is a Scientific American article from 2009 (http://www.scientificamerican.com/article/methane-on-mars-titan/)

Methane (CH4) is abundant on the giant planets—Jupiter, Saturn, Uranus and Neptune—where it was the product of chemical processing of primordial solar nebula material.
... though much of the article is about the formation of methane on Mars, by either life or inorganic (geochemistry) means.

That leaves us with two possible sources: hydrogeochemical and microbial. Either one would be fascinating. Hydrothermal vents, known as black smokers, were first discovered on Earth in 1977 on the Galápagos Rift [see “The Crest of the East Pacific Rise,” by Ken C. Macdonald and Bruce P. Luyendyk; Scientific American, May 1981]. Since then, oceanographers have found them along many other mid*oceanic ridges. Laboratory experiments show that under the conditions prevailing at these vents, ultramafic silicates—rocks rich in iron or magnesium, such as olivine and pyroxene—can react to produce hydrogen in a process commonly referred to as serpentinization. In turn, reaction of hydrogen with carbon grains, carbon dioxide, carbon monoxide or carbonaceous minerals can produce methane.

The keys to this process are hydrogen, carbon, metals (which act as catalysts), and heat and pressure. All are available on Mars, too. The process of serpentinization can occur either at high temperatures (350 to 400 degrees C) or at milder ones (30 to 90 degrees C). These lower temperatures are estimated to occur within purported aquifers on Mars.

Glom
2014-Sep-08, 08:37 AM
Chicken and egg though. How do we get the life to form the complex hydrocarbons from just methane and ethane.

Noclevername
2014-Sep-08, 08:46 AM
Chicken and egg though. How do we get the life to form the complex hydrocarbons from just methane and ethane.

Complex organic chemicals such as amino acids have been found in meteorites, including amino acids not found in living things. Space hydrocarbons can apparently form much more than simple compounds.

Swift
2014-Sep-08, 01:12 PM
People have demonstrated non-lifeform based means to produce complex hydrocarbons (such as amino acids) for at least decades. It is still being studied which of these mechanisms are actually taking place outside of the lab, but there are certainly demonstrations of possible pathways.

I just think that coal or petroleum is unlikely to form from completely non-biological sources (addressing one of cjackson's questions). But other hydrocarbons are completely possible.

Ivan Viehoff
2014-Sep-11, 08:08 PM
Coal has fossils in it. I think we can be reasonably satisfied that coal is not abiotic.

Mineral oils vary substantially in composition, and some light crudes are practically diesel straight out of the ground. I understand the classic authors of the abiotic oil hypothesis (Thomas Gold, was one important one, can't be bothered repeating research, there are old threads in the science and tech branch on abiotic oil) managed to demonstrated feasible natural synthesis routes for abiotic oil consistent with conditions locally available at certain depths in the earth's crust. I think today the consensus view is that some mineral hydrocarbons may well abiotic, but if so they aren't very common in comparison to the biotic stuff. No one prospecting for oil in the places that the abiotic oil hypothesis would suggest has managed to find any.

Clearly abiotic methane is common in places like Neptune. When planetary scientists talk about "ices" they mean frozen forms of stuff like methane as well as water. The bodies coalescing to form earth included icy bodies. The question in earth's case is whether any original abiotic methane from the earth's original formation could have survived the boiling magma world that early earth became, and the answer looks like no. It is controversial whether much of earth's water was original, or came later after earth cooled from a later bombardment by icy impactors. Recent discoveries showing that certain hydrated minerals can survive high temperatures and release water in different chemical circumstances in lower temperatures, and are in fact surprisingly common at certain depths in the crust, have recently suggested the possibility, but not the fact, that more of the water is from the original formation.