Click on "news @ nature.com" above for the full report. Two references cited therein are here and here.

Here are some panspermia-related links:

Definition of panspermia

Are We All Aliens? The New Case for Panspermia

Society for Life in Space

panspermia.org

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Please excuse my ignorance here, there seems to be a presupposition with this theory that life evoled on Mars first and then was seeded here by meteorite impact.

I just wonder if there's any basis in science for this supposition. I suspect there must be, but if so, what is it? Why would Martian oceans evolve life before Terran ones?

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These are "possible" reasons, just off the top of my head. Please take them with a grain of salt.
1) Mars is farther from the Sun, therefore, it cooled earlier than Earth.
2) Mars is smaller than Earth, therefore, it cooled earlier than Earth.
3) Mars was not clobbered by another planet-sized object shortly after it formed, therefore, it cooled earlier than Earth.

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The best reason I am aware of is that Mars has a relatively low escape velocity; therefore material can leave that world after a much less energetic impact, allowing the hypothetical microbes inside to survive more easily.

Any impact that sent Earth rocks into orbit would be so energetic it would probably sterilise the material.

Such impacts, capable of sending Earth rocks into orbit, are also rare;

consider the fact that no material has been found on Earth that originated on Venus, which is of similar size to the Earth; but several meteorites are believed to have come from Mars.

So, logically, if any exchange of living material ever took place in the early solar system, it probably came from Mars (or another small body) to the Earth, rather than the other way round.

That does not prove that it necessarily did.

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I don't understand how bacteria can survive a meteorite impact. I'm sure the temperatures go into the thousands of degrees.

On the surface, yes, but depending on the size, the interior can remain cool. There's quite a few issues - first you have to blast a chunk off of one planet, it has to travel through the rather unfriendly environment of space for, quite possibly, millions of years, then it hits another planet. After all that, it has to land somewhere friendly to life. For all that, bacteria are extremely tough, there are a LOT of them, and they are very small. It isn't necessarily impossible. But right now, it IS speculation. It may be true, it may not, but we just don't know yet.

Incidentally, I wouldn't look to "www.panspermia.org" as a reference. It seems to take a "Creation Science" slant. You'll quickly find, among other things, an "Evolution vs. Creationism" page with complaints about "Darwinists." 'Nuff said.

I believe the panspermia idea goes back as far as Lord Kelvin. Considering all the superstition of the Middle Ages (or even earlier), meteor showers may have caused some thoughts on this idea as well.

It does not explain how life formed, however, only gives it more time elsewhere to form. I suspect it didn't need it but I skipped biology so don't take me too serious.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

I think its an interesting subject. Isn't there evidence of amino acids, or other complex molecules needed by life as we know it, in comets? I recall reading about that a while ago.

I would also bet that bacteria can survive a controlled descent via parachute as well as meteorite impact. So how do we know there isn't life on Mars and we put it there? Sort of a man-made panspermia?