Monday, May 9, 2016

The Origin of Fossil Fuels – A Third Option

Fossil fuels seem to play a decisive role in the industrial grand transition. There is no known substitute to take an alien civilization from depending on plant materials and perhaps some moving water or atmosphere to the next level of energy consumption. Fossil fuels makes an ideal shift from plant materials, as they can be burned for heat and the heat energy used in many, many ways. There is no giant jump of technology, as there is in going from fossil fuels to fission. You just dig them up and burn them. Yet this source of concentrated energy makes possible the change from an agricultural society to an industrial one. The basic key is energy. The vast stores of fossil fuels we have on Earth makes the large technology advance we have seen in the last two centuries possible. On a planet with no or little fossil fuel, the indigenous alien civilization is going to be stuck on a plateau.

Thus, the origin of fossil fuels is an important block of knowledge in determining how many alien civilizations there might be in the Milky Way with star travel capability. An alien civilization can have given up using fossil fuels long ago, but if the planet they originated on did not have any, they would not have star travel capability. Like the origin of life, this gap in our knowledge seriously interferes with our ability to determine the likelihood of aliens visiting.

There are two currently popular theories of the origin of fossil fuels here on Earth. One theory, the biotic, says that hundreds of millions of years of vegetation was buried and decomposed, forming the basic carbon compounds that are fossil fuels today. The various organic compounds that biological organisms consist of were gradually broken down by the heat and pressure of being deep underground, and by some chemical mechanism, the oxygen and nitrogen, phosphorus and potassium mostly migrated out of the pools of gas and liquid hydrocarbons that remained. Solid sources did much the same, but the process in some areas was incomplete. The gas and liquid pools were trapped underground by sedimentary layers, or even salt layers, deposited on top of them, sealing them into the ground until discovered and piped out for energy use.

The other theory is that the masses of hydrocarbons were present since the planet was deposited, and took their own time to separate and segregate, much like various types of rocks do. Gold separates out into nuggets, but it was likely that no gold nuggets plopped down on the planet as it was forming. The heat and pressure of the formation assisted in the separation, and pools formed, rising upwards until stopped by a layer or two of impermeable rock. There doesn't seem to be much doubt that both processes are feasible and have occurred, but it isn't known what fraction of a planet's mass, or specifically Earth's, comes from either, any more than it is known how much of these hydrocarbons still are hidden, deeply buried in the mantle.

Perhaps these hydrocarbons were formed in a third way as well. Here on Earth, we figure that there was a strike of a large planetesimal that created the moon. This would have been an astoundingly ferocious impact, and the heat and shock wave of the impact may have made some major chemical changes in the carbon dioxide and water components of the atmosphere, producing hydrocarbons, which were later buried. What was left of the Earth would have been very active volcanically, producing carbon dioxide as volcanoes are wont to do, which would continue to react with the remaining water to produce more of the same. Was this a large source? Did the vulcanism go on for tens of millions of years? Hard to say.

Let's consider the extreme case, in that impact formation accounts for most hydrocarbons which later becomes fossil fuel. The biotic and abiotic mechanism do work, but only for a small fraction of the amount present on Earth. What does this mean?

It means that fossil fuels in large abundance, large enough to power an industrial grand transition, might be as rare as the likely almost unique impact that made the moon. No one has made any estimates, or at least none are popularly discussed, for how common such an impact would be in some ensemble of planetary disks and solar systems. Probably the requirements for fossil fuel production are not as stringent as those for the early life formation theory, but still they require something big to hit the planet fairly dead on, and leave a planet behind, rather than some smaller clouds of planetesimals, such as the asteroids in our solar system.

There is a bit of a synchronization here, in that if the conditions for life to originate are a narrower subset of those to produce fossil fuel, any alien civilization which manages to get up through the agricultural grand transition will find itself on a planet with a wonderful reserve of the fossil fuels it needs to march through the next grand transitions. It also means that finding suitable planets to seed for the eventual evolution of life will be difficult, if the goal is to have a planet in which an advanced alien civilization, capable of star travel, could some day develop. No fossil fuels, no star travel.

Lacking fossil fuels dooms an alien civilization to not only fall short in technology, but even if some miracle happens and they do pursue technology slowly and steadily, they would be trapped on their home planet. They might be living in a solar system where a nearby planet had suffered an impact early in its life, forming scads of fossil fuels, and they couldn't get there to take advantage of it. Without large sources of energy, such as provided by fossil fuels, the technology they figured out could not be translated into large engineering projects, such as interplanetary mining. Their population would stay small, and their productivity would be small. Together this means there is no rescue for a planet without fossil fuels.

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