You don’t find a lot of creationists among planetary biologists. Even scientists who are also people of faith will typically agree that life is a happy accident involving chemistry, randomness and a whole lot of very slow evolution. But that doesn’t mean an outside power may not have had a hand in getting things started. That power is the impact of comets and meteorites.
Water is plentiful in the universe, but in the early days of the solar system, when Earth was a molten ball of flaming goo, it would have been hard for the proto-planet to stay hydrated. Once things had settled down some, incoming comets, which are little more than water ice and rock and were plentiful in what is known as the heavy bombardment phase of the solar system’s past, could have imported all we needed. Under those wet conditions, the right elements could have started coming together to form precursors to amino acids, then the acids themselves and then, a few jillion steps later, butterflies and bunnies and all the rest. And that initial chemistry wouldn’t even have had to have gotten started on Earth. Amino acids and amino acid precursors have been detected in both comets and meteorites, meaning they could have been imported to us ready-made.
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All the same, there’s one more thing that would help get the basic elements to join hands, and that would be energy—typically in the form of heat. That’s something that ought to be hard to come by in a dirty snowball or a fragment of rock flying through space, but very easy to come by when an impact occurs. A watery object striking a dry body like Earth—or, in the alternative, a dry object striking an icy body like Jupiter’s frozen moon Europa or Saturn’s icy Enceladus—could shock-heat complex organic compounds into existence. Indeed, the Cassini spacecraft has detected those kinds of organics in water plumes that jet out from Enceladus.
Still, you can hardly test your theory by standing on a moon, waiting for a meteor to hit and then sampling the water. So a team of scientists from the U.K.’s Imperial College and the University of Kent came up with another way, one they described in a paper published in this week’s Nature Geoscience.
The researchers first mixed up batches of water with raw chemical signatures matching the various types found in comets—though without any kinds of amino acid precursors. Then they sealed the water in containers and heated it to 932º F (600º C) to ensure that any traces of organic contaminants were destroyed. The water samples were then frozen, and steel projectiles—also heat-sterilized—were fired at them from a gas gun at high speed. Ice plus impact could, in theory, equal organics—and in one sample it did.
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The winning solution was water with a mix of ammonia gas, carbon dioxide and methanol—all carbon, hydrogen, oxygen compounds. That formula produced not just precursors, but amino acids themselves. Give them 4.5 billion years—a longitudinal study if ever there was one—and who knows what they might turn into? The scientists don’t have quite that much time, but lending support to their findings is the fact that computer simulations of the same impact events yield the same chemical results.
“The fact that impacts occur is without question,” the authors wrote. “It is also known that comets contain significant quantities of the compounds used in this study, and that these compounds are found on the impacted surfaces of many of the icy bodies in the outer Solar System.”
Visiting any of those bodies to study the chemistry and confirm the theories is not set to happen anytime soon, but it’s at least on the agenda. NASA is looking at proposals for a robotic mission to Europa, and the European Space Agency has an even more ambitious one planned for launch in 2022. Called JUICE (a somewhat awkward acronym for JUpiter ICy moons Explorer) it will study Europa as well as its sister satellites Ganymede and Callisto. JUICE may not find life, but it will bring us closer to understanding how it got started—on Earth and perhaps on untold other worlds as well.
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