Tim Folger in Nautilus:
While some scientists search for extraterrestrial life by landing rovers on Mars, launching telescopes into space, and scanning the skies with giant radio dishes, geobiologist Joseph Kirschvink thinks that the first telltale signs of alien life may be sitting on a shelf at NASA’s Johnson Space Center, bundled in a Martian rock that conveniently fell to Earth.
On the wall of Kirschvink’s office at Caltech hangs a black and white photo of the meteorite. Radioactive dating shows that the rock formed 4 billion years ago, when Mars was a warmer, wetter place. It was propelled to Earth about 16 million years ago, after a meteorite impact blasted fragments of the Martian surface into space.
Eventually the rock landed on the ice cap of Antarctica, in an area called Allan Hills, where meteorite hunters found it in 1984. Scientists named it ALH84001 after the date and location of its discovery. They traced its Martian origin by analyzing gases trapped in the rock’s pores. Those gases matched the atmospheric chemistry measured by the two Viking spacecraft, which landed on Mars in the 1970s.
What’s more, ALH84001 seemed to contain signs of life, suggesting not only that life could have once existed on Mars, but that it could have made its way to the Earth across the void of space. In fact, Kirshvink thinks it’s likely that life arose only once in our solar system—and that it didn’t start on Earth. “I think there were bacteria on Mars 4 billion years ago,” he says.