Hydrogen. Carbon. Oxygen. Nitrogen. Sulfur. Phosphorous. These elements account for more than 96 percent of the stuff life on Earth is made from — and all six have been found in a rock sample on Mars.

NASA scientists said Tuesday that the Curiosity rover discovered these basic building blocks of life in the very first rock it has drilled from beneath the Martian surface — along with signs that the Red Planet was once capable of hosting primitive microbes.

"It definitely has all the indications of being a habitable environment at one point in time," Michael Meyer, lead scientist for NASAís Mars Exploration Program, said at a news conference in Washington.

The rover's results are filling in a picture of what increasingly appears to have been a very inviting environment — low acidity, full of water, with signs of chemically complementary compounds.

"We have found a habitable environment that is so benign and is so supportive of life that probably if this water was around and you had been on the planet, you would have been able to drink it," said John Grotzinger, lead scientist for the Mars Science Laboratory mission, as Curiosity is officially known.

Grotzinger, a geologist at the California Institute of Technology, was quick to add that "we're not a life-detection mission." Curiosity's analytical machinery isn't built to find life's metabolic remnants, and its cameras wouldn't be able to resolve an image of a fossil microbe if it were staring the rover in the face, he added.

Still, the findings fired up the imaginations of NASA officials.

"I feel giddy," said John Grunsfeld, a former astronaut who now serves as an administrator for the space agency's Science Mission Directorate. "I have an image now of possibly a lake, a freshwater lake, on a Mars with probably a thicker atmosphere."