NASA's Curiosity Mars Rover has found signs of nitrates or compounds that could have provided the essential nutrients needed by the living creatures that might have existed on the Red Planet in the past.

Examining rock and dust samples previously collected by Curiosity, NASA scientists discovered the evidence of nitrates in Martian rock. On the Earth, nitrogen compounds are a vital source of nutrients for living things.

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Nitrate (NO3-) consists of oxygen and nitrogen and is an important source of nitrogen for plant and animal life.

Nitrogen is essential for growth and reproduction in both plants and animals. It's found in amino acids that make up proteins; in nucleic acids that comprise the hereditary material and life's blueprint for all cells and in many other organic and inorganic compounds.

The Sample Analysis at Mars (SAM) instrument aboard Curiosity found significant concentrations of nitrate in soil and rock samples Curiosity collected at three different spots near its landing sites: Rocknest, John Klein and Cumberland.

The John Klein and Cumberland samples previously allowed rover team members to conclude that the area was part of a potentially life-supporting lake-and-stream system billions of years ago. The discovery of fixed nitrogen contributes to this habitability scenario.

A nitrogen study released March 23 reports ancient Mars had a form of nitrogen that could potentially have been used by microbes to build key molecules such as amino acids, that is, if these microbes existed at all.

"Had life been there, it would have been able to use this nitrogen," said Jennifer Stern of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of the nitrogen study.

"People want to follow the carbon, but in many ways nitrogen is just as important a nutrient for life," said Stern. "Life runs on nitrogen as much as it runs on carbon."

The findings further support the idea Mars could once have hosted habitable environments that would have supported life.

Nitrogen is also a key component of the nucleobases that make up RNA and DNA, and of amino acids, the building blocks of proteins.

"It's more support for this environment that would have had the ingredients that life would have needed," said Stern.

The nitrogen study was published in the journal Proceedings of the National Academy of Sciences (PNAS).