Bacteria extraterrestrial

Let us imagine that an extraterrestrial civilization wanted to study our planet s life and decided to send a spaceship on Earth once every million years. For at least 2000 times, the answer would have always been the same The dry lands are completely sterile, and in the seas there are only colonies of bacteria. After that, the dispatches would have been slightly different "Now there are small amounts of oxygen in the atmosphere, and the seas are also inhabited by bigger cells which... 

Westall, F., 1999, The nature of fossil bacteria. A guide to the search for extraterrestrial life, J Geophys Res, 104 (E7) 16437-16451. 

Taylor et al. (2000) primarily described the cosmic spherules in the South-Pole suite of particles because the unmelted MMs were difficult to distinguish from the terrestrial particles. The ice from which the extraterrestrial particles of the South-Pole suite were recovered was deposited during a period of about 400 years between AD 1100 and 1500. The diameters of these cosmic spherules range from 50 to 1,000 pm and the grain-size distribution is assumed to be unbiased because all the particles that fell on the snow surface were preserved in the ice without appreciable losses by chemical weathering or attack by bacteria. 

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