Meteor impacts are generally regarded as monstrous killers and one ofthe causes of mass extinctions throughout the history of life. Butthere is a chance the heavy bombardment of Earth by meteors during theplanet's youth actually spurred early life on our planet, say Canadiangeologists.
A study of the Haughton Impact Crater on Devon Island, in theCanadian Arctic, has revealed some very life-friendly features atground zero. These include hydrothermal systems, blasted rocks that areeasier for microbes to inhabit, plus the cozy, protected basin createdby the crater itself. If true, impact craters could represent some ofthe best sites to look for signs of past or present life on Mars andother planets.
A presentation on the biological effects of impacts isscheduled for Monday, 8 August, at Earth System Processes 2, a meetingco-convened by the Geological Society of America and GeologicalAssociation of Canada this week in Calgary, Alberta, Canada.
The idea that meteor impacts could benefit or even createconditions suitable for the beginning of early life struck CanadianSpace Agency geologist Gordon Osinski while he and colleagues wereconducting a geological survey of the 24-kilometer (15-mile) diameterHaughton Crater. Along the rim of the crater they noticed what lookedlike fossilized hydrothermal pipes, a few meters in diameter.
"That set the bells ringing about possible biologicalimplications," said Osinski. Hydrothermal systems are thought by manypeople to be the favourable places for life to evolve."
Detailed mineralogical analyses have since revealed that whenthe Haughton meteor smacked into the icy ground 23 million years ago itcreated not only a crater, but fractured the ground in such a way as tocreate a system of steamy hydrothermal springs reaching temperatures of250 degrees C. The heat appears to have gradually dropped over a periodof tens of thousands of years, the researchers report.
Besides providing heat and cracking the ground, the impactalso created pore spaces in otherwise dense granitic rocks, givingmicrobes more access to the minerals and the surfaces inside the rocks- basically more real estate and more supplies.
The shocked rocks are also more translucent, which would bebeneficial to organisms that possessing with any photosyntheticcapabilities.
A crater shape itself also might serve as a protectiveenvironment, says Osinski. As such, impact craters are also good placesto store evidence of past life. On Earth many craters fill with waterand become lakes. Lakes accumulate sediments, the layers of which are ageological archive of the time after the crater formed. The HaughtonImpact crater, for instance, contains the only Miocene-age sediments inthe entire Canadian Arctic.
"One of the most interesting aspects of the Haughton ImpactCrater is that it's in a polar desert," said Osinski. The dry, frigidweather makes for a barren landscape that's easy to study, he said. Thesame features make it one of the more Mars-like places on Earth.
"Most people put impacts with mass extinctions," said Osinski."What we're trying to say is that following the impact, the impactsites are actually more favorable to life than the surroundingterrain."
It's interesting to note, says Osinski, that on Earth theheaviest meteor bombardment of the planet happened at about the sametime as life is believed to have started: around 3.8 billion years ago.Impact craters of that age were long ago erased on Earth by erosion,volcanic resurfacing and plate tectonics.
But other planets and moons - including Mars - still bear thecosmic scars of that early debris-clogged period in the solar system.It may be possible, therefore, that the best places to look for atleast fossil evidence of life on Mars is inside those very samecraters, he said.
"What we're doing is trying to narrow down the search area," said Osinski.
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