Kieren Torres Howard of the Meteorite Working Group, and colleagues have discovered organic material in glass created from a meteor impact.
via New Scientist
Remnants of an ancient swamp have been found preserved inside glass created during a meteorite strike. The discovery marks the first time that traces of life have been found to survive the heat and pressure of an impact, adding weight to arguments that microbes travelling on space rocks could have seeded the solar system.
Astrobiologists have long suggested that simple life forms could have hitched a ride to Earth inside meteors, or that impacts on early Earth could have sent terrestrial microbes to other worlds on ejected pieces of our planet. We know that rocks kicked up by impacts can travel vast distances. Martian meteorites with soil trapped inside have landed on Earth, and theoretical calculations suggest that meteor strikes on Earth could have had enough energy to send rocks as far away as the moons of Jupiter and Saturn.
But this concept, called panspermia, also assumes that the organic compounds essential to life as we know it can survive the extreme pressures and temperatures of a crash-landing. Now, evidence has been found around Darwin crater in Tasmania, which was formed by an impact about 800,000 years ago.
Glass created when rock melted during the impact is strewn in a 400-square-kilometre field around the crater. Kieren Torres Howard was conducting doctoral research at the University of Tasmania in Hobart, Australia, studying the distribution and composition of the impact glass. Taking a closer look with an X-ray diffraction machine, he found that the glass is unexpectedly shot through with tiny spherical inclusions. The glass is also riddled with geometrically regular pockets, like a honeycomb.
Howard and colleagues ground up the glass and sorted through the fragments with an acupuncture needle to pick out the inclusions, the largest of which was about 200 micrometres across. Chemical analysis showed that the inclusions were rich in organic material similar to that in a peat swamp, including cellulose and polymers that might derive from leaf cuticles.
“They looked really pristine,” says Howard, who is now at the City University of New York in Brooklyn. “It’s not just that you see a signature of organic materials, it’s almost as if you took the signature of a swamp today.” Previous evidence found at the crater site, including a species of burrowing crayfish that has probably lived in the area for the past million years, had suggested that the region was a swamp or rainforest when Darwin crater was formed.
“That’s what allowed us to really believe we’d found some organics. We knew this was a swamp impact,” says Howard. The team think that a meteor smacked into the ground and melted some of the upper rock to form the impact glass. Bits of plant matter found its way into the molten glass as everything was hurled away by the impact. The water and other volatile compounds in the plants immediately boiled, making a bubbling froth that froze inside the glass as it cooled, creating the honeycomb of pockets.
“I think it is well argued, and they made a very interesting discovery,” says Christian Koeberl of the Natural History Museum in Vienna, Austria, who was not involved in the new work. “It is the first time to my knowledge that organic material has been found preserved in such a way within impact glass.”
So could pieces of an ancient swamp on Earth have gone flying off into space? It’s plausible, the team says, and organics trapped inside glass would be somewhat protected from cosmic radiation on an interplanetary journey. “That’s when the implications get much more funky,” says Howard. “There’s not much challenge in dispersing this stuff. Some material might end up on the moon, some might end up on Mars. The material would be ejected into space in a well-preserved state.”
NASA’s Curiosity rover may have already found Martian impact glass at its home in the Red Planet’s Gale crater, according to a presentation at the Geological Society of America meeting in Colorado last month. Curiosity doesn’t have the dexterity to pick up these shards and run analyses on them, says John Mustard of Brown University in Providence, Rhode Island. But such glasses could be good targets for future sample-return missions aiming to bring Mars rocks back to Earth. Scientists here could then run tests to see if terrestrial material has landed on Mars, or if the glass contains preserved traces of long-lost Martian vegetation.
“Could it have been the mechanism by which panspermia happened? Sure,” says Mustard. “It allows the packaging and interplanetary transfer of organic material.”