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

Question: What first interested you aboutrn the search forrnalien life? 

PaulrnDavies: I suppose myrninterest in looking for life elsewhere in the universe really dates backrn to myrnteens.  What teenager doesn’t lookrnup at the sky at night and think am I alone in the universe?  Well most people get over it, but Irnnever did and though I made a career more in physics and cosmology thanrnastrobiology I’ve always had a soft spot for the subject of life becausern itrndoes seem so mysterious.  To arnphysicist life looks nothing short of a miracle.  It’srn just amazing what living things can do and so thatrnsense of mystery, that sense of how did it all begin has always been rnthere inrnthe background and then in the 1990s I began to take a more active part,rn beganrnto study the prospects that life could spread from Mars to Earth or rnmaybe Earthrnto Mars and that maybe life began on Mars and came to Earth, and that rnidearnseemed to have a lot of traction and is now accepted as very plausible, rnand sornI was asked to help create the Australian Center for Astrobiology.  I was living at that time in Australiarnand we set this thing up in Sydney and I worked there for some years rnbeforernmoving to Arizona.

Question: How much credence has the rntheory that life beganrnon Mars gained? 

PaulrnDavies: Well I firstrnsuggested the idea in the early 1990s that life could have come from rnMars tornEarth inside rocks blasted off the red planet by comet and asteroidrnimpacts.  I think a lot of peoplernfelt that this was a pretty crackpot notion, but it became clear during rnthern1990s that not only that there is a large traffic of material exchanged rnbetweenrnMars and Earth, but that microbes are hardy enough if protected by the rnrock,rncocooned inside, to survive the harsh conditions of outer space for a rnlongrntime, many millions of years, and the evidence both theoretical and rnexperimentalrnhas firmed up and I think many people now realize that if you get life rnonrneither Mars or Earth you’ll get it on both planets from this splashingrnphenomenon.  Now the case for itrnbeginning on Mars is not very strong. rnMars is a smaller planet, so it cooled quicker, so it was ready rnfor lifernsooner.  Conditions there were morerncongenial for life to get going, but as we don’t know how life ever got rngoingrnthis is a bit of a leap in the dark, so we certainly can’t say that itrndefinitely started on Mars, but it seems very plausible that it did.  On Mars seems as good a place as Earthrnfor life to get started.

Question: Is this theory still rncontroversial, and how couldrnit be verified? 

PaulrnDavies: I thinkrnastrobiologists are comfortable with the idea that it could have startedrn onrnMars and come here.  As I’ve saidrnthe evidence is not compelling, but to really clinch this we would of rncoursernneed to either go to Mars and find life there and discover it is the rnsame lifernas we have here on Earth or just possibly a sample return mission, whichrn hasrnbeen long awaited by the astrobiology community.  Thisrn is a spacecraft that will be sent to Mars and pick up arnsort of grab bag of rocks and bring them back to Earth so they can bernstudied.  It’s just possible wernwill find traces of life in those rocks. rnIt’s equally possible we won’t, so it’s a bit of a long shot.  The only way to be really clear is tornhave some expedition to Mars and my feeling is that life on Mars today rnisrnalmost certainly, if there at all, deep under the ground, maybe a rnkilometer orrnso beneath the surface, and so that is going to be hard to get at.

Recorded April 15, 2010
rnInterviewed by Austin Allen