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31 “many great and small fragments carrying seed and living plants and animals would undoubtedly be scattered through space. . . . If at the present instant no life existed upon this earth, one such stone falling on it might. ... lead to its becoming covered with vegetation.” Acknowledging that this hypothesis may seem wild and visionary, Kelvin maintained that it was not unscientific.*° Kelvin’s vision gained credibility during the 1980s, when scientists dis- covered that some meteorites found in Antarctica actually were pieces of Mars, blasted off the red planet by impacts. More than 5 billion Martian rocks capable of carrying living microbes have fallen to Earth in the past 4 billion years.”” We have found so many of them that mail-order houses offer samples for sale. Ro wens AL enn wen Tad Lee ea dante Tart NAA nee ee ee dt NE A group of researchers led by geologist David McKay reported in 1996 that a chunk of Martian rock contained possible chemical signs of ancient life. Most provocatively, McKay’s team spotted shapes that might be micro- fossils of tiny bacteria, resembling some found on our own planet.”* By implication, Earth and Mars were not quarantined from each other; if life started either on Earth or on Mars, it could have spread to the other. RTA QA £6 02010 242-4 NAA Oe 9 Ba dle en nn wk ee et te ee NASA officials saw the McKay group’s findings as so important that they asked President Clinton to announce them to the public, a scene borrowed by the film “Contact.” The McKay team’s interpretations have been chal- lenged by other researchers, leaving the issue unresolved.” Recent research suggests that life may have started earlier on Mars, which cooled off more quickly and stabilized its surface earlier than our own planet. (Percival Lowell, who believed that evolution on Mars was further along than evolution on the Earth, would have enjoyed hearing that.) Some scientists believe that tiny fossils—mineralized communities of microorganisms—still might offer the best hope for finding evidence of past life on the red planet.* Could the ancestors of life on Earth be Martian microorganisms, trans- ported to our planet in chunks of rock? That might explain why life on Earth is separated into three distinct lineages, suggested Stanford’s Norman Sleep; these might represent three distinct sowings of Martian seed.*! There is a downside to this theory. If Earth and Mars can contaminate each other, it may be very difficult to determine if there were two indepen- dent origins of life. If hardy “nanobacteria” exist, relics of ancient life such as those found in the meteorite from Mars might be the descendants of interstellar colonists. A group of scientists who studied this question reported that no meteorite from a planet of another solar system has ever landed on Earth. However, other researchers have found interstellar dust grains in our solar system; Was Arrhenius Right after All? Was Arrhenius Right after All?