Terraforming
Almost everyone interested in Mars knows about terraforming, the process of making Mars more like Earth. The terraformation process, as imagined by scientists and science fiction writers, will result in a thicker atmosphere, flowing surface water and enough water in the atmosphere to create clouds and rain. It could take thousands of years before a viable atmosphere is created (1).
Imagine if terraforming is successful, that we in the near future have traveled to Mars and started to live there, permanently. A thicker and stronger Martian atmosphere would enormously affect the current surface. Resurfacing, the combined efforts of erosion and deposition would become stronger, especially when liquid water becomes the main resurfacing agent. Currently mostly the wind resurfaces Mars, which is much weaker then water.
The difference between Earth and Mars
Should terraforming be successful Mars would look more like Earth, but there would be one big difference: Mars is, as far as we know, not tectonically active. There is wind activity and at the poles CO2 ice is in a cycle of deposition and sublimation every year due to the seasons, but no plate tectonics is active. On Earth the movements of crustal plates cause mountains and ocean basins to form, creating positive relief. The compressive movement of crustal plates causes a mountain belt to rise higher and higher. However, erosion by wind and water will immediately attack the mountain and rivers subsequently carry the eroded material to lower elevations where it is deposited as sediment. The movement of the Earth’s crust has been active for billions of years and has regenerated high relief landscapes for water and wind to attack.
On Mars, on the other hand, no geological active crust is present. The planet is, so to speak, tectonically dead. It wasn’t dead during its first billion years, however. At that time the surface was constantly being resurfaced by impacts and volcanism. Volcanism became more localized and created an enormous bulge, the Tharsis Bulge. On the flanks of Tharsis enormous volcanoes originated, of which one of them, Olympus Mons, is the highest volcano in the solar system (27 kms). During this era the northern hemisphere became what it is today: much lower and less cratered then the southern hemisphere. Scientists do not know exactly what caused this hemispheric ‘dichotomy’, although the lower amount of craters has been linked to a resurfacing event. After this enormous volcanic episode water took over. Footprints of this water flow era can be seen on images from Mars: enormous outflow channels cut kilometer deep into the bedrock and flowing towards the northern lowlands.
The last billions of years, however, mostly only wind erosion attacked the surface. Wind is much less an erosive force then water. Further more, the atmosphere is currently very thin (1/1000 the thickness of the terrestrial atmosphere at sea level) which lowers the erosive force of wind even more.
Eroding to death
Therefore, in short, Mars, without an active crust, will erode to death. This means that high regions will be eroded and deposition will take place at low regions. This process will continue until all rocky high relief has been eroded and the planet has an even layer of soft sediment, which will be redeposited all the time by wind and water. This will also affect the climate; wind patterns on Mars are thought to be controlled by the great differences in relief, like Tharsis and the dichotomy.
Perhaps Mars will eventually look like one big dune field, except for a possible northern ocean inside the northern highlands. But if deposition will occur mainly in the low regions this ocean could eventually become clogged-up by sediments and the water would distribute evenly over the planet or in patches of lakes throughout a dune covered planet. Plant growth will play an ambiguous role. On Earth plant roots help rock to break because it slowly widens cracks in the rocks causing the rocks to loosen. Plant growth will also create a protective layer over the soft sediment causing wind erosiveness to decrease.
Luckily Mars has an enormous relief, so this scenario of a dune Mars will probably not happen soon (within human time scales). Eroding down a mountain on Earth takes millions of years anyway. But still, erosion will attack the Martian surface, with no process to create new rocky surfaces. Terraforming, in the form of a temperature increase, will immediately attack the surface, starting with the disappearance of the polar deposits.
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