More evidence of life on Mars as soon as 2012

Biological reactions often favor one isotope of an element over others. Such reactions can therefore leave signatures in the isotope ratios.

The Mars Science Laboratory rover is scheduled to land in 2012. It has a mass spectrometer that will be able to measure sulfur isotope abundances.

If sulfur 34 is depleted in sulfides compared to in sulfates, this would, on Earth, be an indication that microbes had converted the sulfates into sulfides.