Researchers have identified rocks that they say could contain the fossilised remains¹ of life on early Mars.

研究人员在火星上发现一些岩石，称这些岩石很可能藏有早期火星生命的化石。

Scientists believe life could have existed on Mars almost four billion years ago

The team made their discovery in the ancient rocks of Nili Fossae.

Their work has revealed that this trench²（沟渠，战壕） on the dark side of Mars is a "dead ringer" for a region in Australia where some of the earliest evidence of life on Earth has been buried and preserved in mineral form.

They report the findings in the journal Earth and Planetary Science Letters.

The team, led by a scientist from the Search for Extraterrestrial Intelligence（外星人） Institute (Seti) in California, believes that the same "hydrothermal（热水的） " processes that preserved these markers of life on Earth could have taken place on Mars at Nili Fossae.

The rocks there are up to four billion years old, which means they have been around for three-quarters of the history of Mars.

When, in 2008, scientists first discovered carbonate（碳酸盐） in those rocks the Mars science community reacted with great excitement; carbonate had long been sought as definitive³ evidence that the Red planet was habitable - that life could have existed there.

Carbonate is what life turns into, in many cases, when it is buried - if it does not turn in to oil. The white cliffs of Dover, for example, are white because they contain limestone⁴（石灰岩） , or calcium⁵ carbonate.

The mineral comes from the fossilised remains shells and bones and provides a way to investigate the ancient life that existed on early Earth.

In this new research, scientists have taken the identification of carbonate on Mars a step further.

Adrian Brown from the Seti Institute, who led the research, used an instrument aboard Nasa's Mars Reconnaissance Orbiter called Crism to study the Nilae Fossae rocks with infrared⁶ light.

Then he and his team used exactly the same technique to study rocks in an area in north-west Australia called the Pilbara.

"The Pilbara is very cool," Dr Brown told BBC News. "It's part of the Earth that has managed to stay at the surface for around 3.5 billion years - so about three quarters of the history of the Earth."

"It allows us a little window into what was happening on the Earth at its very early stages."

And all those billions of years ago, scientists believe that microbes formed some distinctive⁷ features in the Pilbara rocks - features called "stromatolites（叠层） " that can be seen and studied today.

"Life made these features. We can tell that by the fact that only life could make those shapes; no geological process could."

This latest study has revealed that the rocks at Nili Fossae are very similar to the Pilbara rocks - in terms of the minerals they contain.

And Dr Brown and his colleagues believe that this shows that the remnants（残余） of life on early Mars could be buried at this site.

"If there was enough life to make layers, to make corals or some sort of microbial homes, and if it was buried on Mars, the same physics that took place on Earth could have happened there," he said. That, he suggests, is why the two sites are such a close match.