Does Life Exist on Mars?

Martian Meteorites

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Of the approximately 22,000 meteorites found on the Earth, only 18 are thought to be of Martian origin. These meteorites are said to be from Mars due to (1) the type of igneous rock they are made of, a type unusual here on Earth. The fact that these are igneous rocks means that they were formed from volcanic activity and must therefore be from a planet instead of say, an asteroid. (2) These meteorites are mostly younger than the thousands of meteorites found on Earth. They are 1.3 billion years old versus the usual 4.5 billion-year-old samples indicating that they must have formed on a planet after the formatin of the solar system. (3) Perhaps the most convincing evidence that some meteorites are from Mars is the atmosphere trapped in little bubbles in the rocks. This ratio of gases in this atmosphere is unlike that found on Earth, but matches the atmosphere the Viking missions found on Mars. Mars' atmosphere is thought to have changed very little in the past few billion years and so the atmosphere trapped billions of years ago in meteorites would be very similar to the atmosphere we find on Mars today.

One of the Martian meteorites recently stirred up great interest when NASA scientists announced in the August 1996 issue of Science that they had found what may be evidence for life in Martian meteorite ALH84001. Unlike other Mars meteorites which are around 1.3 billion years old, ALH84001 was 4.5 billion years old, suggesting that it was part of the original crust formed on Mars. A type of rock called carbonate was found in the meteorite. Carbonate is formed from liquid H₂O (water) and CO₂ (carbon dioxide) gas, on Earth sometimes with the help of life. The carbonate in ALH84001 was formed about 3.9 billion years ago. The rock was ejected from the Martian surface and sent on its way to Earth, probably by a meteoriod, about 17 million years ago. It is believed to have been on Earth for approximately 11,000 years before it was discovered in 1984 in Allyn Hills, Antarctica.