The grandaddy of ALH84001 crystallized 4.5 by ago. Then sometime between 3.6 - 4 by ago, during the period of the late heavy bombardment which occured in the inner Solar System, the grandaddy of ALH84001 was fractured by a large impact. This is supported by the observation that ALH84001 underwent at least two shock heatings separated by a period of annealing. Presumably, the second shock event was the one which ejected ALH84001 into space 16 My ago.
During the time of the first shock, Mars's Atmosphere was considerably wetter than today (as suggested by modeling and surface features) and it is postulated that water seeped into AL84001. Because the water was saturated with atmospheric carbon dioxide, carbonate materials were deposited into the fissures with the subsequent formation of the evidence:
Evidence for Biology
Four lines of attack (all indirect except for the fossils):
2. Teardrop-shaped crystals of magnetite and iron sulfide embedded in places where the carbonate is dissolved. Certain terrestrial bacteria use such crystals as compasses to find their way. Huh. But, Mars currently has no magnetic field to speak of. What's the deal?
3. PAHs (polycyclic aromatic hydrocarbons)
4. Elongated and Oval-shaped structures within the carbonate===> teeny fossils. Really tiny fossils; Typical Terrestrial bacteria are ~ 0.5 - 20 microns long ( E. Coli, roughly 1-2 micro-meters in length, roughly 1-2 micro-meters in length); "Martians" are 20 - 100 nanometers. There are suggestions that fossils of comparable sized organisms have been found on the Earth in Eastern Washington ( nanobacteria).
