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Washington University geologists have developed new theoretical calculations about how life might have arisen from volcanic gases on Earth, Mars and other celestial bodies.
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 & Sciences, and Mikhail Y. "Misha" Zolotov, Ph.D., senior research scientist, describe a scenario in which initial volcanic gases spewing from the Earth as hot as 1,200 degrees Celsius cool down to a relatively low temperature of 150-300 C. Shock and Zolotov have shown that, in this temperature range, environmental and chemical conditions are ripe for formation of basic hydrocarbons -- a wide range of carbon-based compounds essential for life -- from the hydrogen and carbon monoxide present in the volcanic gases.
For decades researchers observing volcanic rocks have detected a fine film of organics on the rocks' mineral surfaces, leading to endless speculation about the film's source. Many thought that the organic compounds were stable parts of the Earth's mantle brought up over time through volcanic activity. Others held that the organic mixtures condensed and coalesced in volcanic gases during eruptions. The Shock-Zolotov calculations show that the latter process is more likely.
Conditions favorable for hydrocarbon synthesis also could 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 setting up experiments and testing results, and they should be integral in analyzing Martian meteorites. They could, in fact, help settle controversy about the 1996 analysis of a Martian meteorite, which bore evidence of the same kinds of organics found in many terrestrial volcanic lava, magma and ash samples.
Shock and Zolotov published their results in the Journal of Geophysical Research. Their work was supported by the National Science Foundation and NASA.
The calculations show that life can arise not only from the gaseous crucible of present-day terrestrial volcanoes, but that it was even more likely to have developed 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 Celsius hotter than it is 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 C.
"These conditions might have contributed to the production of organic compounds required for the emergence of life," said Shock, who first rose to prominence in the "origins of life" debate in 1992 when he performed calculations showing that 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 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 Mount St. Helen 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 said. "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, or through a chain of events sparked by lightning, or in volcanic gases.
"Unlike spark discharge scenarios, the processes we are pursuing to study the origins of life here or on Mars are normal, daily geological processes," Shock said. "The volcanic gas scenario is one of the most approachable. The evidence is readily accessible, and we know we can extrapolate from evidence here to Mars and other bodies without much ambiguity."