'BUILDING BLOCKS FOR LIFE'

Analysis shows the Gale Crater rock contains carbon dioxide, in addition to hydrogen, oxygen, phosphorus, sulfur and nitrogen.

Carbon dioxide provides a key ingredient in the building blocks for life, all of which have now been found in the Mars rock sample, Grotzinger said.

The $2.5 billion, nuclear-powered Curiosity rover landed inside the giant Gale Crater impact basin, located near the Martian equator, on August 6 for a two-year mission.

Scientists were drawn to the area because of a three-mile (5-km) mountain of sediment, called Mount Sharp, rising from the crater floor. But shortly after the rover's landing, the team decided to first explore the Yellowknife Bay area, located in the opposite direction from Mount Sharp.

Observations from Mars orbiters showed three different types of terrain coming together in Yellowknife Bay, plus a low elevation, all hints that water could have once flowed and pooled on the surface.

That hunch was verified with the first chemical analysis of material drilled out from inside what appears to be a slab of bedrock, named John Klein, after a mission manager who died in 2011. Scientists don't know the rock's age, nor how it formed. They suspect, however, that the John Klein rock is at least 3 billion years old and that it spent enough time in non-acidic and not-too-salty water for various telltale clays and minerals to form.

"This rock, quite frankly, looks like a typical thing that we would get on Earth," Grotzinger said. "The key thing here is this is an environment that microbes could have lived in and maybe even prospered in."

The habitable conditions in Yellowknife Bay appear to roughly coincide within a couple of hundred million years of the first evidence for life on Earth.

"On Earth, finding organics in very, very ancient rocks is a difficult proposition," said Paul Mahaffy, principal investigator for Curiosity's Sample Analysis at Mars, or SAM, instrument.

Finding organics on Mars may be even more challenging. Without much protection from an atmosphere, ultraviolet and cosmic radiation can destroy organics. Mars also apparently is covered with chemicals, known as perchlorates, that consume organics.

"The search for organic carbon is an issue for this mission and you want to do this as deliberately as possible. You don't just want to wander around and try stuff out," Grotzinger said.

Knowing that Mars at least had the ingredients for life, however, makes the search for organics more viable.

"This is not a simple problem, but I think the mission is up to it and we're really excited to get started on that now," Grotzinger said.