Mars is frequently viewed as having a fairly uniform surface of basaltic rock, the type of dense rock that makes up most of Earth’s ocean crust. However, new findings made using the ChemCam on the Curiosity rover suggest that it may once have been different.

The ChemCam which uses lasers to analyze the composition of rocks it encounters recently came across unusually light colored rocks, similar to those found in the continental crust of Earth.

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

The rocks were found inside the Gale Crater, where Curiosity landed. According to the researchers they are about 4 billion years old and are rich in feldspar and possibly quarts, making them similar to rocks contained in Earth’s continental crust.

The 22 rock samples analyzed bear a strong resemblance to Tonalite-Trondhjemite-Granodiorite or TTG according to Violaine Sautter. Sutter is first author of the new study which appears in Nature Geoscience.

TTG was a dominant feature in the continental crust of the Earth more than 2.5 billion years ago, during the Archean era.

The Gale crater site was originally selected by NASA because, much like the Grand Canyon on Earth, it provides a glimpse into the ancient history of the Martian crust. The 96 mile wide crater, created 3.6 billion years ago, is 1-2 miles deep allowing Curiosity to examine the geologic periods of Mars.

In March, researchers announced that Mars once had an amount liquid water on its surface equivalent to the volume of the Arctic Ocean. While some of this water remains in the Martian ice caps, much of it was lost to space.

All of this serves to reinforce the idea that Mars may have started along a path similar to the one taken by Earth. It is even possible that it was habitable for a very long time.

“With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting it might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard in March.

One of the great mysteries of the Red Planet is what happened to set Mars on the path that led to its current state.