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In the 1970's NASA thought it had answered the question 'Is
there life on Mars?'. The majority of the experiments on the
Viking spacecraft indicated no biological activity; the one
apparently positive result was interpreted as a chemical reaction.
Whilst the space exploration of Mars was stopped in its tracks,
laboratory studies of the planet on Earth received an unexpected
boost when it was found we already had rocks from Mars!
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A structure about 100nm in length suggested as a fossil from Mars in meteorite ALH 84001 |
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In martian meteorites, carbonates have been found accompanied by organic matter; all living things leave evidence of their existence in the form of organic compounds or chemical fossils, even though no tangible fossil form can be seen. The organic matter in the meteorites, like the fossils, is controversial, there is no proof that it got there before the sample reached Earth. However, the scenarios proposed for how it might have entered the rock on our planet are equally implausible.
The only way to reconcile the problem is to go to Mars and seek in situ evidence of organic matter, associated with features and minerals related to flowing water. From the age of various of the meteorites we know that water was around certainly 1.3 billion years ago and maybe as recently as 600,000 years (pictures provided by NASA's Global Surveyor show features attributable to recent water activity).
In any investigation done on Mars, however, the signs of life must be sought in locations where the harsh oxidising environment has been prevented from destroying the evidence. Such a place will be within the interiors of rocks or in the soil shielded by large boulders.
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