Evolutionary history of Mars – Københavns Universitet

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Evolutionary history of Mars

The evolution of the planet Mars is roughly divided into three eras: The Noachian, the Hesperian, and the Amazonian. The eras were named after areas on Mars which were formed in those time periods.

The timing of the eras is based on the study of impact crater density on the Martian surface, based on the argument that older regions have more craters. However since there are several competing models describing the rate of meteor impacts on Mars, the timing of the periods is still debated, and the ages given below are only approximate.

The topmost map shows areas from the three eras: Noachian (orange), Hesperian (green) and Amazonian (blue). The bottommost map shows the elevation of different areas on Mars.

The Noachian era

The Noachian era is the oldest of the three time periods and lasted from Mars' beginning, about 4.5 billion years ago, to about 3.7 billion years ago. Geological features in Noachian areas on Mars such as dried up river valleys and delta features suggest that the climate may have been warmer and more humid in this period. For such a climate to be possible, the atmosphere must have been thicker than it is today. Volcanic activity took place during the Noachian era and the volcanic Tharsis region was formed during this time period.

The Hesperian era

The Hesperian era lasted from about 3.7 billion years ago to about 3 billion years ago. During this time period the Martian climate began to change to drier, dustier conditions. Water that might have flowed on the Martian surface during the Noachian era may have frozen as underground ice deposits. During the Hesperian extensive lava plains formed.

The Amazonian era

The Amazonian era began about 3 billion years ago and continues to the present. Amazonian Mars has been mostly dry and dusty, but there are signs that water was sometimes released onto the surface locally from underground through sudden floods. Olympus Mons, the largest known volcano in the Solar System, has been formed in this period.

The mystery of the lost atmosphere

It is still debated what could have caused the disappearance of the supposed dense atmosphere and humid climate of the Noachian era. It has been suggested that such a climate change could have been caused by the turnoff of the global magnetic field in the Noachian era followed by an ejection of almost all of the early Martian atmosphere into space due to heavy impacts and solar wind stripping combined with CO2 being absorbed into the regolith and deposited in the polar caps.