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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.

The finding, hidden from scientists for more than 15 years in the magnetic structure of a well-studied meteorite found in Antarctica, presents a serious alternative to the idea that life on Earth arose spontaneously out of some primordial soup.

The bottom line: Our ancestors may have been Martians.

The study by researchers at Caltech, Vanderbildt and McGill universities reveals that a Mars rock known as Allan Hills, thought since 1996 to contain fossilized remains of Martian bacteria, remained cool enough to sustain embedded microbial life during its violent ejection from Mars and subsequent 16 million-year journey to Earth.

Amazingly, even during a fiery entry through Earth's atmosphere, the interior of the rock never got much hotter than a bad summer day in New York City -- 105 degrees Fahrenheit (40 degrees Celsius).

Leading scientists from several fields said the research renews vigor in the idea that life on Earth could have come from somewhere else, part of a broader theory called panspermia.

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.

Melosh, who was not involved in the research but had previously shown that rocks could be ejected from planets without being overheated, says mounting evidence shows any life that might have existed millions of years ago on a wetter, warmer Mars could have traveled to Earth.

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.

After eons of wanderings, Earth's gravity finally got hold of the rock and reeled it in. That was sometime between 11,000 and 13,000 years ago.

Researchers found the meteorite in 1984, stuck in Antarctica's Allan Hills ice field. A 1996 study of the rock claimed to find fossilized trails of microbial life that originated on Mars. Many scientists doubted the finding, saying the features could have been created on Earth or might not have indicated microbial life at all.

Debate has swirled around the rock ever since.

But even if Allan Hills is dead as a doornail -- the meteorite does not contain actual life, only the apparent signatures of life -- the new study demonstrates that space rocks are capable of acting as vessels for the transport of organisms around the solar system.

Like an interplanetary shuttle service for life as we know it.

And there seems to no shortage of shuttles: Experts estimate that roughly a ton of Martian rocks fall on Earth every year. More than a dozen have been found, while others bury themselves in sand or ice, or disappear into the seas.

"Our findings give a boost to panspermia, since they are the first experimental evidence that a rock could be transferred from one planet to another without being heat sterilized," said Benjamin Weiss of the California Institute of Technology and lead author of the study.

The study is published in the October 27 issue of the journal Science.

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.

But Brownlee and his coauthor, paleontologist Peter Ward, contend that while complex life might be rare, microbial life could be widespread in our galaxy and elsewhere. And Brownlee pointed out that where there is microbial life, there can be lots of it: Typical terrestrial soils have billions of bacteria per gram, he said.

"If there's microbial life on Mars, it must be carried to Earth," Brownlee said, adding that the new study tells us it is more likely that these microbes could arrive intact.

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.