Biogenic and abiogenic graphite in minerals and rocks of the early earth

Abstract

Minerals and rocks older than 3.7 billion years in age have attracted investigators looking to find evidence for traces of life. However, ancient rocks are heavily metamorphosed, leaving only graphitized organic matter. In addition, abiogenic graphite is ubiquitous in ancient rocks, creating difficulties for researchers seeking to claim true traces of life. Previous investigations searching for traces of life, based in Jack Hills (Australia), Akilia and Isua (Greenland), and Nuvvuagittuq (Canada), are summarized in this chapter. Graphite accompanied by low δ13C values was found at all these localities. However, whether or not this graphite has a biogenic origin is the subject of debate. Rocks from the >3.7 Ga Isua supracrustal belt provide robust evidence of traces of life in the form of well-preserved sedimentation features of reduced carbon accompanied by low δ13C values. The occurrence of graphite with low d13C values in ancient rocks cannot be used to indicate the presence of a microbial biosphere on the early Earth unless the age of the carbonaceous material is confirmed as the same age of host rock sedimentation.