The oldest geological features recognizable on Mars belong to the Noachian era, named after Noachis Terra in the southern highlands. In fact, most of Mars’s rugged southern highlands are of Noachian age. This era was characterized by very high cratering rates and the formation of the major impact basins (e.g., Hellas and Argyre); major episodes of volcanic activity; and the formation of the oldest valley networks. Lying immediately atop Noachian geological units are features of the Hesperian era. Much of the northern lowlands and, in particular, the ridged plains are of Hesperian age. The youngest major surface features on Mars belong to the Amazonian era, so named because they are typified by the plains and volcanic materials of Amazonis Planitia. The surfaces of the prominent volcanos of Elysium and Tharsis Montes are of Amazonian age. The absolute ages of martian features and thus the time history of the planet’s evolution are currently uncertain. Converting the relative chronology implied by stratigraphy relationships requires that the absolute ages of key surface features be determined, and this will almost certainly require a sample-return mission. In the meantime, observations of the density of craters in a region can be used as a means of estimating that region’s absolute age.2 In other words, if a surface has a greater density of craters than an adjacent region and the rate at which impacts have occurred over time is known, then the ages of the surfaces can be estimated. Unfortunately, this technique is dependent on imperfect models of the cratering rate at Mars through time, which are, in turn, extrapolated from the known absolute chronology of the Moon. Page 25, An Astrobiology Strategy for the EXPLORATION of MARS by Committee on an Astrobiology Strategy for the Exploration of Mars Space Studies Board, Division on Engineering and Physical Sciences, Board on Life Sciences, Division on Earth and Life Studies
Posted on: Tue, 07 Oct 2014 05:22:13 +0000
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