From: Washington University in St. Louis
Posted: Monday, March 27, 2000
Geologists at Washington University in St. Louis have developed new theoretical calculations on how life might have arisen on Earth, Mars and other celestial bodies from volcanic gases.
Analyzing ash, lava and magma chemical compositions from nine representative volcanoes around the world, geologists Everett L. Shock, Ph.D., professor of earth and planetary sciences in Arts and Sciences at Washington University, and Mikhail Y. Zolotov, Ph.D., senior research scientist, describe a scenario where initial volcanic gases spewing from the Earth as hot as 1200 degrees Celsius cool down to a relatively low temperature of between 150-300 degrees C. Shock and Zolotov have shown that, in this temperature range, environmental and chemical conditions are ripe for basic hydrocarbons -- a wide range of carbon-based compounds essential for life -- to form from the hydrogen and carbon monoxide present in the volcanic gases. They say that a naturally occurring catalytic reaction, similar to a famous industrial process called Fischer-Tropsch synthesis, involves the iron compound magnetite as catalyst, and is an essential part of the process.
For decades researchers observing volcanic rocks have detected a fine film of organics on mineral surfaces of the rocks. This led to endless speculation about the source of the organic film. Many thought that the organic compounds were stable parts of the Earth's mantle brought up over time through volcanic activity. The other perspective was that the organic mixtures condensed and coalesced in volcanic gases during eruptions. The calculations show that the latter process is more likely.
Conditions favorable for hydrocarbon synthesis also may be favorable for other life ingredients, such as amino acids and complex organic polymers, leading, perhaps, to self-replicating RNA molecules and eventually to all sorts of cells and diverse organisms.
The calculations take into consideration temperatures, gas composition, oxidation states of the gases and geophysical conditions of the individual volcanoes. They are valuable as a framework for researchers to set up experiments and test results, and they should be integral in analyzing Martian meteorites. They could, in fact, help settle a dispute over whether the controversial analysis of a Martian meteorite in 1996 -- which bore evidence of the same kinds of organics found in many terrestrial volcanic lava, magma and ash samples -- is indicative of fossil evidence or else a similar non-biologic pathway that Shock and Zolotov describe.
Shock and Zolotov published their results in the Jan. 2000 issue of the Journal of Geophysical Research. Their work was supported by the National Science Foundation and NASA.
The calculations show not only that life can arise from the gaseous crucible of present day terrestrial volcanoes, but that it was even more likely to develop billions of years ago on early Earth, Mars and Jupiter's satellite, Europa. There is a solid body of evidence that shows the temperature of magma then would have been about 200 degrees C hotter than now and that the atmosphere would have been less oxidized. The Shock/Zolotov calculations show that higher initial temperatures of spewing volcanic gases are more favorable for organic synthesis, once the gases dilute and cool to the hydrocarbon-forming zone of 150-300 degrees C.
"These conditions might have contributed to the production of organic compounds required for the emergence of life," says Shock, who first rose to prominence in the "Origins of Life" debate in 1992 when he performed calculations that showed life could have first emerged chemosynthetically -- without sunlight -- at hot water vents on the ocean floor. "Our work began with an eye toward understanding the hydrocarbons found in Martian meteorites, but we soon realized that there are plenty of gas compositions from Earth's volcanoes, and we thought we should study the full range of possibilities. So, with this paper we analyzed the hard physical evidence from the Earth, and, from that, we think we can extrapolate to Mars.
"The calculations prove what can happen thermodynamically, but not necessarily what will happen. Developing them is an important first step in understanding this process. For the first time, we now have a quantified temperature zone in which hydrocarbons can form, and a framework to understand what conditions lead to hydrocarbon formation from volcanic gas. There have been a number of experiments in this area over the years, but not a framework to better understand the process. Misha's (Zolotov's) calculations predict what kinds of chemical clues one should see based on the organic compounds that are present.'
Zolotov gathered data from volcanoes ranging from Mt. St. Helen's and Iceland's Surtsey to Sicily's Mount Aetna and Hawaii's Kilauea. All of the volcanoes arose from different geological settings and produced initial gas temperatures of varying ranges.
"The calculations show that there is a potential for hydrocarbons to form during the cooling process, and that this condition also is promising for amino acids to develop, " Zolotov says. "The process is not very efficient today. For instance, at Kilauea, the hydrogen and carbon monoxide amounts of the gases are no more than 2 percent. But it still is a steady source for hydrocarbons to form."
As for the origins of life -- on Earth, at least -- there are two basic competing views: One suggests that life was brought here by comet or meteorite impacts or interplanetary dust; the other that life was generated here, either at the ocean floor, through a lightning spark that touched off an atmosphere that produced organic compounds in watery environments, or in volcanic gases. All scenarios involve organic compounds.
"Unlike spark discharge scenarios, the processes we are pursuing to study the origins of life, here, or on Mars, are normal, daily geological processes. The volcanic gas scenario is one of the most approachable,' says Shock. "The evidence is readily accessible, and we know we can extrapolate from evidence here to Mars and other bodies without much ambiguity."
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