A fist-sized meteorite nicknamed "Black Beauty" could unlock vital clues to the evolution of Mars from the warm and wet place it once was to its current cold and dry state, the US space agency Nasa said.
Discovered in Morocco's Sahara Desert in 2011, the 320-gram space rock contains 10 times more water than other Martian meteorites and could be the first to have originated on the planet's surface or crust.
After more than a year of study, a team of US scientists determined the meteorite was formed 2.1 billion years ago at the start of the most recent geologic period on Mars, known as the Amazonian, Nasa said.
The abundance of water molecules in the meteorite - about 6,000 parts per million, 10 times more than other known rocks - suggests water activity persisted on the Martian surface when it was formed.
It is generally accepted that Mars had abundant water early in its existence, causing scientists to ponder if life might once have existed there. But the nature of its evolution to a cold and dry place remains a mystery.
"Many scientists think Mars was warm and wet in its early history, but the planet's climate changed over time," said lead scientist Carl Agee.
Known technically as NWA (Northwest Africa) 7034, "Black Beauty" is made of cemented fragments of basalt, a rock that forms from rapidly cooled lava.