While critics noted there are ways to make light carbon in the absence of life, Harrison considers those possibilities to be "extremely unlikely," especially in light of another discovery of rocks in Western Greenland, not far away, of the same age, and a similar ratio of 12C to 13C.
The scientists see light carbon inclusions in a phosphate mineral called apatite, which is also the material of which bones and teeth are made.
The form of life the researchers believe they have discovered was probably a simple microorganism, although its actual shape or nature cannot be ascertained, Mojzsis said, because heat and pressure over time have destroyed any original physical structure of the organisms.
Harrison said of UCLA's ion microprobe and the research: "The individual samples are very small, and no other instrument would have been sensitive enough to reveal precisely the isotopic composition and location of the carbon inclusions in the rock."
It is unknown when life first appeared on Earth, which is approximately 4.5 billion years old.
The residue of ancient life that the scientists believe they have found existed prior to the end of the "late heavy bombardment" of the Moon by large objects, a period which ended approximately 3.8 billion years ago, Harrison noted.
"Life is tenacious, and it completely permeates the surface layer of the planet," Mojzsis said. "We find life beneath the deepest ocean, on the highest mountain, in the driest desert and the coldest glacier, and deep down in the crustal rocks and sediments."
Source:University of California - Los Angeles