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.