The geology of Mars from studies of martian meteorites

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Until robots or humans are sent to Mars and bring back samples, martian meteorites are the only samples of Mars that we have available for study. We know they are from Mars because gas trapped within them matches the composition of the martian atmosphere as measured by the Viking landers. These meteorites provide us with an opportunity study the geology of another planet. All of the martian meteorites are similar to basalts from the Earth. By analogy with the Earth, we know that these rocks were formed by crystallization of magma that was melted out of the martian mantle. This melt ascended to the surface of Mars, where it cooled and crystallized. There are also minerals within the meteorites that are evidence for the activity of water percolating through the rocks. In addition we have pockets of glass that formed when local areas within the rock were heated, as a result of the impact that lofted the rock into space and started its journey to Earth. These pockets of glass are where the martian atmosphere is found.