It could be easier to detect the signs of ancient life on Mars than it is on Earth, say scientists connected with Nasa's next rover mission.
The six-wheeled robot is due to touch down on the Red Planet in 2021 with the specific aim of trying to identify evidence of past biology.
It will be searching for clues in rocks that are perhaps 3.9 billion years old.
Confirming life on Earth at that age is tough enough, but Mars may have better preservation, say the researchers.
It comes down to the dynamic processes on our home world that constantly churn and recycle rocks - processes that can erase life's traces but which shut down on the Red Planet early in its history.
"We don't believe, for example, that Mars had plate tectonics in the way Earth has had for most of its history," said Ken Williford from Nasa's Jet Propulsion Laboratory (JPL) in California.
"Most of Earth's rock record has been destroyed by subduction under the ocean crust. But even the rock left at the surface is heated and squeezed in ways it might not have been on Mars.
"So, paradoxically, it may well be that the older rocks on Mars are better preserved than much younger rocks on Earth," he told BBC News.To read more, click here.