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These layered hills, seen in this false color image of part of Arabia Terra on Mars, may have a watery origin. Arabia Terra is a mountainous region in the northern hemisphere of Mars, dating from the Noachian geological era of the Red Planet, around four billion years ago. Considering the region’s great age, it sports numerous craters, often within which are layered mounds such as those in this image of NASA’s Mars Reconnaissance Orbiter.
The stratified rocks of Arabia Terra come in three forms. The first type, seen in this image, is described by alternating layers of light and dark matter, which may represent episodic periods of sediment deposition. One can imagine an ancient lake filling the crater in which these mounds are found, the shoreline changing as sea levels varied with the Martian climate, the tides leaving behind alternating layers of mudstone and limestone. Or maybe the layers signify different volcanic events that interrupted the usual deposition processes by dumping layers of ash on the mounds.
The second type consists of layers that appear to be made of the same material and form “ stepped ” mesas, while the third type has dark, thin layers of rubbery, irregular material and often produces rocks that roll over them. slopes. This third type could be the result of lava having once flowed through a sandy region; thereafter, the basalt rock hardened, and on the edges of the cliffs where the sandy material crumbles, the larger pieces of basalt rock eventually give way and roll to the bottom of the crater. Image: NASA / JPL – Caltech / University of Arizona.
