The earliest evidence of life comes from the Isua supercrustal belt in Western Greenland, and from similar formations in the nearby Akilia Islands. This is because a high level of the lighter isotope of carbon is found there. Living things take up lighter isotopes because this takes less energy. Carbon entering into rock formations has a concentration of elemental δC of about −5.5. of C, biomass has a δC of between −20 and −30. These isotopic fingerprints are preserved in the rocks. With this evidence, Mojzis suggested that life existed on the planet already by 3.85 billion years ago.