1960s, they were taken as evidence of plate tectonics. Researchers believe these magnetic stripes on Mars are evidence for a short, early period of plate tectonic activity. When the rocks became solid they retained the magnetism that existed at the time. A magnetic field of a planet is believed to be caused by fluid motions under the surface. However, there are some differences, between the magnetic stripes on Earth and those on Mars. The Martian stripes are wider, much more strongly magnetized, and do not appear to spread out from a middle crustal spreading zone. Because the area containing the magnetic stripes is about 4 billion years old, it is believed that the global magnetic field probably lasted for only the first few hundred million years of Mars' life, when the temperature of the molten iron in the planet's core might have been high enough to mix it into a magnetic dynamo. There are no magnetic fields near large impact basins like Hellas. The shock of the impact may have erased the remnant magnetization in the rock. So, magnetism produced by early fluid motion in the core would not have existed after the impacts. When molten rock containing magnetic material, such as hematite (Fe2O3), cools and solidifies in the presence of a magnetic field, it becomes magnetized and takes on the polarity of the background field. This magnetism is lost only if the rock is subsequently heated above a particular temperature (the Curie point which is 770 °C for iron). The magnetism left in rocks is a record of the magnetic field when the rock solidified. Other features Interactive Mars map See also Climate of Mars Geology of Mars Glaciers on Mars Groundwater on Mars Impact crater List of craters on Mars Martian gullies References Recommended reading Grotzinger, J. and R. Milliken (eds.). 2012. Sedimentary Geology of Mars. SEPM. Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14 Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences. External links Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention Terrae on Mars Phaethontis quadrangle Memnonia quadrangle