A meteorite from Mars has been found to contain 10 times as much water as other similar rocks from Mars.
The astonishing find has been called a "missing link" between the planet's previously hot, warm and wet climate and its current cold, dry environment.
The NWA 7034 meteorite, nicknamed "black beauty", was found in the Sahara Desert in 2011, in Morocco.
It formed about 2.1 billion years ago at the start of the so-called "Amazonian" geological period on the Red Planet.
Scientists suggested the rock was once volcanic lava which cooled in one of Mars' now-lost oceans.
It is "significantly older" than other Martian meteorites, according to Nasa scientist Mitch Schulte, at the Mars Exploration Program.
"We now have insight into a piece of Mars' history at a critical time in its evolution," he said.
Above: the NWA 7034 meteorite
Nasa explained that the rock is made from cemented fragments of basalt, rock that forms from lava which has been quickly cooled. It can help researchers learn about the volcanic activity on the planet, as well as what its surface looked like during that period.
It's not known specifically how the meteorite left Mars and came to Earth, but it is thought the impact of an asteroid on the planet may have sent it into space.
There are 110 other known meteorites which have fallen to Earth from Mars.
"This Martian meteorite has everything in its composition that you'd want in order to further our understanding of the Red Planet," said Carl Agee, leader of the analysis team and director and curator at the University of New Mexico's Institute of Meteoritics .
"This unique meteorite tells us what volcanism was like on Mars 2 billion years ago. It also gives us a glimpse of ancient surface and environmental conditions on Mars that no other meteorite has ever offered."