Published online by Cambridge University Press: 22 October 2009
These lines of evidence indicate that Mars and the earth were formed of a mixture of iron and silicate phases which was nearly uniform, and that the earth has formed a core during geologic time and Mars has not.
(Harold Urey)Mars is the only body in the Solar System, apart from the Earth and Moon, to which we devote more than one chapter in this enquiry of planetary crusts. Information now available for Mars, from telescopic observations, orbiters, landed missions and martian meteorites, is enormous and accordingly details now known about the martian crust are considerable. An important finding is that Mars has been geologically active throughout its history and yet still retains a rock record dating back to about 4.5 Gyr, the age of the oldest martian meteorite. Sedimentary deposits are recognized both in some of the oldest and youngest exposed terrains. Accordingly, Mars may well have the most completely preserved geological record of any terrestrial planet.
For both the Moon and Earth, chapters are broken out according to crustal types (primary, secondary, tertiary) and age (Hadean, Archean, Post-Archean). For Mars, we take a different approach. Mars differentiated into core, mantle and crust very early in its history, likely due to magma ocean processes. Unlike Earth, there is unambiguous evidence for this early differentiation. The composition and subsequent evolution of the crust in turn has been greatly influenced by this early history.
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