Monday, March 19, 2007

Abiogenic Petroleum or: Where Does Gas Come From?

Okay, so abiogenic petroleum doesn't sound very interesting, but it's been bugging me the past couple of days, so I'll explain. Asking where fossil fuels come from seems like a daft question - they're made from the remains of organisms that lived millions of years ago. Certainly that's the conventional theory, but on my meanderings around the web, I've discovered that it certainly isn't the only alternative. From the Environmental Literary Council:

The prevailing explanation for the formation of oil and gas deposits is that they are the remains of plant and animal life that died millions of years ago and were compressed by heat and pressure over millions of years. Russian and Ukrainian geologists argue that formation of oil deposits requires the high pressures only found in the deep mantle and that the hydrocarbon contents in sediments do not exhibit sufficient organic material to supply the enormous amounts of petroleum found in super-giant oil fields.

The abyssal, abiotic theory of oil formation has received more attention in the West recently because of the work of retired Cornell astronomy professor Thomas Gold, who is known for development of several theories that were initially dismissed, but eventually proven true, including the existence of neutron stars. He has also been wrong, however; he was a proponent of the "steady state" theory of the universe, which has since been discarded for the "Big Bang" theory. Gold's theory of oil formation, which he expounded in a book entitled The Deep Hot Biosphere, is that hydrogen and carbon, under high temperatures and pressures found in the mantle during the formation of the Earth, form hydrocarbon molecules which have gradually leaked up to the surface through cracks in rocks. The organic materials which are found in petroleum deposits are easily explained by the metabolism of bacteria which have been found in extreme environments similar to Earth's mantle. These hyperthermophiles, or bacteria which thrive in extreme environments, have been found in hydrothermal vents, at the bottom of volcanoes, and in places where scientists formerly believed life was not possible. Gold argues that the mantle contains vast numbers of these bacteria.
A lot more can be found at Wikipedia. Deep in the Wired archives is an interesting interview with Thomas Gold, where he discusses his theories about the origins of petroleum and life:

What first made you think that there might be life at such depths?

It was in response to the long debate over how helium, which is concentrated in oil, could be associated with petroleum and biological debris. Helium has no affinity chemically with biological stuff. My argument was that the helium must have been swept up from below by petroleum from deep down, and that led me to the whole notion of the deep biosphere.

And you believe that the oily depths where you found magnetite represent the environment where life on Earth began?

Yes. You can only suppose the origin of life in circumstances where there is no direct access to the source of at least one of the components that you require. If you have the common story of the warm pond on the surface, then all of the things that are needed will be accessible to whatever microbes there are. So they will multiply exponentially up to the limit of the food supply. That means that in a flash the whole thing is done and they are all dead. There has to be a process of metering out at least one of the components so it's impossible to eat up everything at once. The hydrocarbons from the mantle provide that metered supply. If life developed down below, it could later crawl up to the surface and invent photosynthesis.

As I understand it, you think that any planetary body that's warm enough for liquid water at some depth, and that has hydrocarbons in it, will have a deep biosphere. So there could be life inside the moon.

What we know about the moon is quite remarkable. The astronauts of the Apollo program left behind a gadget that measures molecular weights. There were a few deep earthquakes measured, and in association with those earthquakes there was always a molecular mass of 16 recorded by the instrument. Now the people who don't know any chemistry then responded saying, Well, that's oxygen. But it's no good telling me it was oxygen atoms because an oxygen atom could not go a centimeter through cracks in the rock. What fairly stable molecule have we got that has mass 16? Methane. So it is warm enough for life in the moon. Mars is undoubtedly a better candidate because it's larger and has more internal heat. Then there are the satellites of the major planets, also Triton, Pluto, Charon, and the larger asteroids that have big black markings on them. Not Venus or Mercury - there the water would disappear altogether. In my first paper on the subject I advised that one should go down the deep valley on Mars and to the landslides that have come off its walls in the hope of finding solid material residue that we have identified as coming from microbial action.

I guess we'll know for sure, when we start investigating the deep interior of our planet, and other bodies in the solar-system.