2011 Volume 120 Issue 5 Pages 877-885
The oldest record of life is a carbonaceous material preserved in 3.9-3.8 Ga metamorphosed sedimentary rocks in western Greenland. The carbonaceous material is now graphitized due to extensive metamorphism, although it exhibits a low 13C/12C ratio. The 13C-depleted isotopic composition is comparable to organics produced through biological carbon fixation, so it could support the biological origins of the graphite. This interpretation has been debated for 15 years. Here, the on-going controversy is briefly reviewed. In summary, geologists have good reason to believe that life emerged on Earth at least in 3.8 billion years ago.