Add another mark to the tally of how similar Mars is to Earth. While evidence continues to mount for water on the Red Planet, an unexpected new piece of research has found that it may have a continental-like crust once thought unique to Earth, suggesting it had tectonic activity long ago, possibly in its first 100 million years.
It may also rule out the theory that Mars experienced a large impact early in its history, resulting in its northern hemisphere being much lower than the southern hemisphere.
The intriguing discovery, published in Nature Geoscience, was made by Violaine Sautter of the Museum of Natural History in Paris and her colleagues. They analyzed data from 20 rocks studied by the ChemCam instrument on the Curiosity rover and suggested that they originated from a continental crust, rather than basaltic rock, due to the abundance of silica which is similar to what we observe in our own continental crust.
On Earth, our continental crust is thought to have originated from the movement of magma when plate tectonics first formed billions of years ago. Previously, the crust on Mars was thought to be one piece – that is, unlike Earth, it had no tectonic plates that shifted on the surface. But this latest evidence suggests otherwise. Tectonic activity on Mars would have occurred “very early” Sautter notes, roughly from the time of its formation 4.57 billion years ago to 4.47 billion years ago.
The evidence from Gale Crater, shown by the marker, may explain why the northern hemisphere (blue) is so much lower than the southern hemisphere (orange and red). Credit: Google Mars/NASA
“It is very important, because Mars is supposed to be a basalt covered world,” Sautter told IFLScience. Until now, it had been impossible to find evidence for a continental crust from orbit, but Curiosity’s location – Gale Crater – is unique in that it is deep, giving a cross section across the geological history on Mars, and it is also at the border of the northern and southern hemispheres.
This is important, because the hemispheres pose a problem. For some reason, the northern hemisphere is several kilometers below the southern hemisphere, appearing as a large depression. The predominant theory had been that Mars was struck by a Pluto-sized body four billion years ago, but this discovery may suggest otherwise. “To some extent yes, this paper [rules out a large impact],” Sautter explained.
The continental crust, rich in silica and feldspar, could explain the different altitudes of the two hemispheres. Sautter explains that it may be the result of an “internal reason” under the surface of Mars, such as the non-symmetrical transfer of heat, “not by an external [event] such as a giant impact.” Sautter estimates that the continental crust would extend 50 to 70 kilometers (30 to 45 miles) below the surface, and the researchers note in their paper that parts of it could have melted into a “hot and soft lithosphere” on the Red Planet.
The presence of a continental crust will require further research before it can be confirmed though. This might be possible on NASA’s upcoming InSight mission, which will land in September 2016 and drill five meters (16 feet) into the ground. If it is present, it poses further questions about just how Earth-like Mars once was.
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