What's puzzling is that the remaining meteorites have ages in the billions of years. Age was determined by measuring certain radioactive isotopes within the rock. The composition and age of the young meteorites indicate that volcanoes on Mars had been active in the recent geologic past. Mars Global Surveyor, orbiting and imaging Mars since 1997, has returned images that indicate young volcanic deposits on the surface. A simple explanation that all the young samples left Mars together, from an area of recent volcanism, as a result of asteroid impact.
Results indicate the young samples left Mars by four different impacts.
In total, all studied Martian meteorites come from nine ejection events. As a result, there is speculation that Mars was volcanically active much longer than previously accepted. Ingrained theories hold that geologic activity on Mars ended billions of years ago. This problem also cast doubts on the accepted rate that meteor craters appear on Mars. Scientists hope an automated mission to retrieve material from known locations on Mars will help them make sense of these Martian meteor mysteries.