The group members hopped between the islands on a tiny yellow fishing dinghy. Day after day, they drew maps of the rock layers and chipped away dozens of samples with their geology hammers. This banded iron was the source of the rock Mojzsis had used to make the claim for ancient life. Analyzing samples in his laboratory back at UCLA, he had found minuscule bits of carbon, which appeared to have come from living matter. Not all carbon comes from something once alive, Mojzsis explained, but scientists have devised a test for a biological origin.
Carbon comes in several forms, or isotopes, that differ by weight.
So the remains of living matter contain relatively less carbon-13. The carbon collected from this banded-iron layer held a clear signature of ancient life, Mojzsis said. It actually held even more information. Whatever had left the carbon in this rock had been evolving for some time. It would appear, he said, that life had thoroughly taken over the planet even earlier than 3.85 billion years ago - if the dating of the rock was correct.