Analysis of carbon isotopes in sediment samples taken from half a dozen exposed locations, including an exposed cliff, leave researchers with three plausible explanations for the carbon's origin — cosmic dust, ultraviolet degradation of carbon dioxide, or ultraviolet degradation of biologically produced methane.
The researchers note today (Jan.17) in Proceedings of the National Academy of Sciences that "All three of these scenarios are unconventional, unlike processes common on Earth."
Carbon has two stable isotopes, 12 and 13. By looking at the amounts of each in a substance, researchers can determine specifics about the carbon cycle that occurred, even if it happened a very long time ago.
"The amounts of carbon 12 and carbon 13 in our solar system are the amounts that existed at the formation of the solar system," said Christopher H. House, professor of geosciences, Penn State. "Both exist in everything, but because carbon 12 reacts more quickly than carbon 13, looking at the relative amounts of each in samples can reveal the carbon cycle."
