That means the total volume of lava piles up into one, very large volcano. Because magnetic fields in general act to shield planets from many forms of cosmic radiation, this discovery has important implications for the prospects for finding evidence of past life on the Martian surface. Study of the ancient magnetic field also provides important information about the interior structure, temperature and composition of Mars in the past. The presence of magnetic fields also suggests that Mars was once more of a dynamic Earth-like planet than it is today. Of fundamental importance are the age and composition of different types of rocks on the Martian surface.
Geologists use the age of rocks to determine the sequence of events in a planet's history.
Composition information tells them what happened over time. Particularly important is the identification of rocks and minerals formed in the presence of water. Water is one of the keys to whether life might have started on Mars. Future orbiting and landed missions will carry special tools designed to help answer these questions. Twelve Mars meteorites discovered on Earth can also give us clues about the planet.