Study Puts Hole In Comet Theory Of Life's Origin

Astervitude writes "A new study by US and Japanese scientists has put a serious dent into one version of the popular panspermia theory that credits comets for bringing the seeds of life to Earth. Surveys conducted by the University of Arizona, the National Astronomical Observatory of Japan and others now show that objects from the main asteroid belt between Jupiter and Mars were largely responsible for the period of Late Heavy Bombardment that ended 3.9 billion years ago. UA Professor Emeritus Robert Strom believes that no more than 10 percent of the Earth's water comes from comets and any oceans then extant would have been 'vaporized by the asteroid impacts during the cataclysm.'" Interesting, because this directly contradicts the Nova mini-series Origins that just finished running on PBS. Science never stops moving.

Re:So why does this contradict panspermia?

[StuckInSyrup]

If conditions were right, that initial small pocket of bacteria or virii could multiply to cover the planet in a matter of years.

I do not disagree completely, but one word is definitely wrong in this sentence. Virii.
A virus is a parasitic lifeform, that "lives" only inside of a living cell. No cell - no life, no multiplication, no evolution and no spreadnig. Outside of a living cell a virus is an inactive lump of protein and nucleic acid.
Other tahn that, a virus is a potent driver of evolution by mixing up its host genome, possibly creating new genetic structures.

Re:So why does this contradict panspermia?

[smallfeet]

%60 of systems seem to be binary or trinary, not good for life to develope. Planets would need to be in the "goldylocks" zone where water is liquid much of the time. And there are about 5-6 other factors that would limit development of life elsewhere. There will still be a lot of good planets, but not anywhere near as many as you suggest.

Contradictions abound!

[edunbar93]

This theory also directly contradicts another theory I saw this month in Sky and Telescope [skyandtelescope.com], which referred to this article [nature.com]. This one is for the formation of the outer gaseous planets and the kuiper belt. The basis of the theory is that the orbits of all the gas giants should have been closer to the sun, as they would have required a much denser gas-and-dust cloud than would have existed as far out as they are now. As well, the kuiper belt would have formed closer to the sun.

Due to gravitational interactions between the gas planets and the kuiper belt objects, Jupiter's orbit shrinks and Saturn, Uranus and Neptune expand, with the latter two actually changing place and moving into much more elliptical orbits before settling down into their current orbits. These larger orbits put both planets squarely into the primordial kuiper belt and, well, cause the Late Heavy Bombardment.