Small Molecule Interactions Were Central To The Origin Of Life
Mars Rock Cool Enough to Transport Life to Earth
By Robert Roy Britt
In a discovery that has scientists rethinking where they came from, a groundbreaking study has revealed that living organisms could emigrate through the solar system in the relatively cool womb of a space rock, spreading life with little more fanfare than the arrival of a shooting star.
Are we all aliens?
"The study demonstrates clearly what we had previously only speculated about -- that the conditions of launch, space transit and reentry are not too harsh for dormant spores and other microorganisms to survive," said Jay Melosh, a geophysicist at the University of Arizona's Lunar and Planetary Laboratory.
The long, rocky road to Earth
The Allan Hills meteorite, also called ALH84001, may be the most studied and debated rock in the universe. Made of stuff thought to be 4.5 billion years old, the object was carved from a half-mile (1 kilometer) under the Martian surface about 16 million years ago when an asteroid or comet hit the Red Planet.
How about interstellar seeding?
The panspermia theory holds that the seeds of life are everywhere, and that life on Earth could be the result of germs or other dormant organisms that traveled here from another star system, then evolved into spiders and lizards, Labradors and lawyers.
Researchers familiar with the new Allan Hills study said it does lend support to the idea of interstellar seeding.
However, a rock spending millions of years in interstellar space would face doses of cosmic rays that would likely destroy any genetic material inside a live or dormant creature, said astronomer Donald Brownlee, coauthor of the book Rare Earth.
In an interview, Brownlee characterized a trip from Mars to Earth as much less hazardous, pointing out that for some rocks it takes less than a year.
"I think this is a marvelous interplanetary transportation system, but a transportation system between stars is highly questionable," Brownlee said.
Questionable, but not impossible, others said.
Smarter than a protozoan?
Rare Earth contends that a remarkable confluence of events -- the right chemicals, the right distance from a star, and more -- conspired to allow complex life to develop on our planet, and that we humans may be alarmingly alone in the universe.
How the study was done
Caltech geobiology professor Joseph Kirschvink worked with Weiss and others to test several millimeter-thin slices of the meteorite with a device that detects tiny differences in the orientation of magnetic lines in rock.
Kirschvink had provided less direct evidence in 1997 that the interior of the rock might have remained cool. The new study was to prove out his suspicions.
Slices from near the meteorite's surface showed a magnetic alignment consistent with that of Earth, which was expected: After enduring the heat created by its plummet through the atmosphere, a rock's magnetic field reorients its magnetization, to be aligned to the local field, as it cools.
But deeper inside the rock, the magnetic orientation was found to be random, indicating that the interior had kept its cool. The researchers then heated a slice of the interior to figure out at what temperature it would begin to demagnetize and set itself up for reorientation. That temperature -- 105 degrees Fahrenheit (40 degrees Celsius) -- is a threshold the rock never reached until it came to the lab.
How in the world did it stay so cool inside that rock?
Well, rock isn't exactly the best heat conductor, Weiss said, so it takes a long time for heat to penetrate to the interior.
"For a potato-sized rock entering the atmosphere, the diffusion time to the center of the rock is significantly longer than the several minutes that the rock spends being heated in the atmosphere," Weiss said.
In addition, melted bits fly off the rock's surface, carrying heat away and, as we now know, salvaging the protective womb for any life that might be aboard.Source: www.Space.com, October 26, 2000
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