Mastodons, Mummies, and Meteorites: Evidence of Life Out There?
Scanning electron microscope image of the Orgueil meteorite.
Credit: Dr. Richard Hoover/Journal of Cosmology
The recent publication of the investigation of a rare class of meteorite (the CI1 Carbonaceous Chondrite) by Dr. Richard Hoover of NASA's Marshall Space Flight Center has caused another stir among scientists and the news media regarding possible origins of life on Earth, and life in the Universe in general. Exciting stuff—though the report stimulated the "usual" spectrum of responses, ranging from the starry-eyed wow! to the cool-headed let's wait and see to a tepid-at-best we've heard this hype before….
In a nutshell, Dr. Hoover's study suggests that encased within the minerals of the studied meteorites are chemical signatures of life and fossils of microbes, some of which are very similar to known Earthly cyanobacteria, and some that are not very like Earth life forms at all. The implication is that life (at least these would-be meteoritic microbes) originated outside of Earth, on some other parent body—possibly a comet—and that the formation of life may be common and ubiquitous in the Universe. It's a very big implication—and as some respondents have cited, big implications require big proof (okay, I'm paraphrasing Carl Sagan's, "extraordinary claims require extraordinary proof").
One of the challenges in this type of investigation is in distinguishing between "indigenous" mineral and microbe-like forms in the meteorites (that is, those that may have come along with the meteorite during its fall to Earth) and contamination by Earthly microbes—because, come on, if the Earth's surface is nothing else, it is absolutely teeming with life in every nook and cranny!
Other implications have been mentioned beside life from "out there" seeding the early Earth and giving rise to us (in fact, there is no definitive proof that life originated on Earth—and according to one theory, life could not have started here).
One idea goes the other way: life started on Earth early on, prior to the end of the period of heavy bombardment of our world by asteroids and comets, and the blasts of some of those collisions could have kicked the Earthly specimens back into space…maybe only to return to us eons later as "evidence of extraterrestrial life"—which would be ironic.
As part of his analysis, Dr. Hoover included a range of known Earth life as control references–samples from mastodons, Egyptian mummies, insects preserved in amber, fossilized cyanobacteria from ancient rocks, and several others—to compare to the samples from his subject meteorites. According to his publication, the comparison of the samples has shown certain organic chemicals found in terrestrial life lacking in the meteorites—a number of amino acids, and nitrogen—which suggest that the meteorite samples may not bear contamination by Earthly life.
The quest for life beyond Earth has gone on for a long time, and a lot of tantalizing clues and possible evidence have been making the rounds. Microbe fossils in meteorites from Mars? Life not-as-we-know-it living in the waters of Mono Lake? Methane plumes from beneath the Martian surface? Organic molecules in the tails of comets and on Saturn's moon Titan? And now, possible organics and fossils in the rarest of carbonaceous chondrite meteorites?
For the moment, I'll wait and see how scientists review Dr. Hoover's study—because, yes, I have heard before what turned out to be hype—but in the back of my mind…wow!