So when the ratio of carbon-12
to carbon-13 decreases, it indicates the presence of the kind of bacteria we are looking for," said Haggblom.
Eventually, the commonest isotope of carbon, carbon-12
, was accepted as standard, since this would entail less change in the value of atomic weights generally.
General Electric researchers have synthesized isotopically pure diamonds composed almost entirely of carbon-12
atoms that conduct heat 50 percent better than their natural counterparts.
By measuring the ratio of carbon-13 to carbon-12
in the methane gas, researchers will be able to distinguish whether it came from Martian rocks or from methane-producing microorganisms that may have existed on the planet.
Life-forms preferentially stockpile carbon-12
in their cells, so any ancient substance enriched with carbon-12
could have a biological origin.
, an essential element we're all made of, can only form when three alpha particles, or helium-4 nuclei, combine in a very specific way.
Chemical analyses indicate that the mini-gems contain higher-than-average concentrations of the carbon-12
isotope, researchers report in the July 3 Nature.
Second, future orbiters and landers could measure the isotopic ratio of carbon-12
to carbon-13 in the gas.
The stable isotopes, carbon-12
and carbon-13, are derived from Earth's mantle, and released when carbon-bearing rocks weather at the surface.
Natural diamond is about 99* carbon-12
and 1% carbon-13.
About 99 percent of carbon in non-living stuff is carbon-12
, a lighter version of the element than the carbon-13 that accounts for most of the remaining 1 percent.
That could be because tree leaves prefer to take in gas made of carbon-12
, leaving the heavier version in the air.