Spectra signatures of the shergottites are similar to the Mars' uplands, suggesting that their composition may be common on Mars. None are significantly shocked Their initial isotopic ratios are similar, unlike shergottites. They likely had an igneous origin 1.3 Ga ago. Live 146Sm possibly existed. In many respects, ALH84001 differs from the other martian meteorites.
Isotopic chronologies signify very early mantle differentiation for Mars.
Weathering Rates of Exposed Rocks Mixing Rates of Regolith To fully use the characteristics of martian meteorites to make inferences about Mars, we need to understand the origins of these samples. None of the martian meteorites resided for a significant period at the martian surface, for none show evidence for irradiation by cosmic rays on Mars. Two viable models exist for explaining the space exposure ages of martian meteorites. One assumes that separate cratering events on Mars ejected those meteorites with a common exposure age. The second explanation assumes that all martian meteorites were ejected in one very large cratering event, and that the space exposure groupings were formed by later collisional break-up events in space.