Some unusually light-colored rocks on Mars discovered by NASA's Curiosity rover are surprisingly similar to granitic continental crust rocks of Earth, the first evidence of a potential "continental crust" on Mars, scientists say.

Mars has been thought of as mostly a basaltic planet, covered with dark, relatively dense igneous rocks like those making up the Earth's crust below our oceans.

However, in the Gale Crater where the rover landed, its ChemCam laser instruments analyzed some rocks which were distinctly brighter, the researchers report in Nature Geoscience.

"Along the rover's path we have seen some beautiful rocks with large, bright crystals, quite unexpected on Mars" says Roger Wiens of Los Alamos National Laboratory, lead ChemCam scientist. "As a general rule, light-colored crystals are lower density, and these are abundant in igneous rocks that make up the Earth's continents."

Chemical analysis of the rocks revealed they're rich in feldspar, along with quartz, very similar to the granitic rock of the Earth's continental crust.

"This tells us that Mars is more Earth-like than we ever thought," says Wiens.

"These are rocks with large feldspar crystals and potentially excess silica, so Mars does not just consist of dense, dark-looking rocks, but also has rocks that really look like they could be on any continent on Earth, and that's a first on Mars."

The rocks bear a strong resemblance to a terrestrial type of rock of geologists know as TTG, Tonalite-Trondhjemite-Granodiorite, which made up much of the terrestrial continental crust around 2.5 billion years ago, says study first author Violaine Sautter of the Muséum d'Histoire Naturelle in Paris.

The impact that created Gale Crater created a natural cut-away view that extends 1 to 2 miles deep into the Martian crust, with the light-colored silica rocks found in a layer dating to around 3.6 billion years ago.

Their presence suggests Mars may once have experienced plate tectonics similar to those seen on Earth, the researchers say.

That would be in contrast to the assumption, prevalent until now, that Mars did not experience the kind of magmatic or volcanic activity that would have been necessary for the development of tectonic plates.

The researchers take pains to note that their finding of feldspar-rich magmatic rocks cannot confirm global-scale magmatic activity on the red planet or prove the existence of tectonic plates, but simply suggest it might have been a possibility.

If so, then several billion years ago Mars was probably much more like Earth than has been imagined, says Wiens.

"And that's pretty exciting because Earth is this oasis of life now, and we wonder what Mars was like at one point in time," he says.