Four and a half billion years ago, a rock was formed on Mars by some volcanic process. Half a billion years later, this rock was broken into smaller pieces by a meteorite impact nearby. Some ground water also entered the rock. 16 million years ago, an asteroid hit Mars somewhere near where this rock was. The impact threw pieces of the rock into space. One 2 kilogram piece of rock orbited the Sun until 13,000 years ago, when it came close to the Earth. This piece crashed onto an Antarctic glacier. Over 13,000 years, it reached the Allan Hills region of Antarctica, buried inside the ice. In 1984, this meteorite was discovered and named ALH84001. A large number of people worked out this history of the meteorite that we just narrated.
This year, a team led by David McKay of the American space organization NASA, suggested that there seemed that there seemed to be signs that life may have existed on this rock in some bygone era: The meteorite has some organic molecules, of the same family as naphthalene (which is used in mothballs). When bacteria decay, such compounds are produced. Many meteorites do have such compounds. The meteorite has iron oxide (magnetite) of the sort which some bacteria on Earth secrete. It has iron sulphide, which is produced by some anaerobic bacteria (those that don’t use oxygen). The meteorite has some balls of carbonate material, which may be formed by some material, which may be formed by some living thing. On the other hand, almost all earth bacteria are 100 times larger than this material. The meteorite may contain very small fossils (less than hundred millionth of a millimeter). Nanobacteria are this size.
In 1961, another meteorite was found to have signs of life. But soon these were discovered to be grains of pollen and particles of furnace ash. The signs of life turned out to be from Earth itself. This could be the case for the Antarctic meteorite too. What makes scientist more hopeful is that some of these items mentioned are within cracks, and the cracks could only have been formed before the meteorite came to rest in Antarctica. So maybe, just maybe, the signs of bacterial life that we see are from when the rock was on Mars. In 1976, the Viking spacecraft failed to find any such bacteria on Mars. But maybe they landed in the lifeless part of Mars. Or maybe bacteria were present on Mars millions of years ago, but aren’t there now. Scientists are looking at ALH84001 very, very carefully. And even US President Bill Clinton has promised support for a new NASA spacecraft to Mars.
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