Are Earthlings Martians?

Question: What first interested you about\r\n the search for\r\nalien life? 

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Paul\r\nDavies:  I suppose my\r\ninterest in looking for life elsewhere in the universe really dates back\r\n to my\r\nteens.  What teenager doesn’t look\r\nup at the sky at night and think am I alone in the universe?  Well most people get over it, but I\r\nnever did and though I made a career more in physics and cosmology than\r\nastrobiology I’ve always had a soft spot for the subject of life because\r\n it\r\ndoes seem so mysterious.  To a\r\nphysicist life looks nothing short of a miracle.  It’s\r\n just amazing what living things can do and so that\r\nsense of mystery, that sense of how did it all begin has always been \r\nthere in\r\nthe background and then in the 1990s I began to take a more active part,\r\n began\r\nto study the prospects that life could spread from Mars to Earth or \r\nmaybe Earth\r\nto Mars and that maybe life began on Mars and came to Earth, and that \r\nidea\r\nseemed to have a lot of traction and is now accepted as very plausible, \r\nand so\r\nI was asked to help create the Australian Center for Astrobiology.  I was living at that time in Australia\r\nand we set this thing up in Sydney and I worked there for some years \r\nbefore\r\nmoving to Arizona.

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Question: How much credence has the \r\ntheory that life began\r\non Mars gained? 

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Paul\r\nDavies:  Well I first\r\nsuggested the idea in the early 1990s that life could have come from \r\nMars to\r\nEarth inside rocks blasted off the red planet by comet and asteroid\r\nimpacts.  I think a lot of people\r\nfelt that this was a pretty crackpot notion, but it became clear during \r\nthe\r\n1990s that not only that there is a large traffic of material exchanged \r\nbetween\r\nMars and Earth, but that microbes are hardy enough if protected by the \r\nrock,\r\ncocooned inside, to survive the harsh conditions of outer space for a \r\nlong\r\ntime, many millions of years, and the evidence both theoretical and \r\nexperimental\r\nhas firmed up and I think many people now realize that if you get life \r\non\r\neither Mars or Earth you’ll get it on both planets from this splashing\r\nphenomenon.  Now the case for it\r\nbeginning on Mars is not very strong. \r\nMars is a smaller planet, so it cooled quicker, so it was ready \r\nfor life\r\nsooner.  Conditions there were more\r\ncongenial for life to get going, but as we don’t know how life ever got \r\ngoing\r\nthis is a bit of a leap in the dark, so we certainly can’t say that it\r\ndefinitely started on Mars, but it seems very plausible that it did.  On Mars seems as good a place as Earth\r\nfor life to get started.

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Question: Is this theory still \r\ncontroversial, and how could\r\nit be verified? 

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Paul\r\nDavies:  I think\r\nastrobiologists are comfortable with the idea that it could have started\r\n on\r\nMars and come here.  As I’ve said\r\nthe evidence is not compelling, but to really clinch this we would of \r\ncourse\r\nneed to either go to Mars and find life there and discover it is the \r\nsame life\r\nas we have here on Earth or just possibly a sample return mission, which\r\n has\r\nbeen long awaited by the astrobiology community.  This\r\n is a spacecraft that will be sent to Mars and pick up a\r\nsort of grab bag of rocks and bring them back to Earth so they can be\r\nstudied.  It’s just possible we\r\nwill find traces of life in those rocks. \r\nIt’s equally possible we won’t, so it’s a bit of a long shot.  The only way to be really clear is to\r\nhave some expedition to Mars and my feeling is that life on Mars today \r\nis\r\nalmost certainly, if there at all, deep under the ground, maybe a \r\nkilometer or\r\nso beneath the surface, and so that is going to be hard to get at.

Recorded April 15, 2010
\r\nInterviewed by Austin Allen

The theory that life on our planet originated on Mars was originally dismissed as a "crackpot notion." It’s now considered a distinct possibility.

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