Earth had life earlier than previously thought

Abstract

Until now, the earliest known signs of life on Earth have been 35 billion-year-old microfossils. But new evidence may push the date for emergence of life back to nearly 4 billion years ago, according to a provocative study of one of Earth's oldest rocks. A chunk of sediment from Greenland more than 3.85 billion years old bears chemical traces of life, researchers assert—a hallmark overabundance of carbon-12 relative to carbon-13, found within mineral grains imbedded inside the sediment [ Nature , 384 , 55 (1996)]. Oceanography professor Gustaf Arrhenius and geology graduate student Stephen J. Mojzsis at Scripps Institution of Oceanography in La Jolla, Calif., and colleagues at the University of California, Los Angeles, were able to accurately analyze the carbon specks, which are only micrometers in diameter. Their results imply that life existed on Earth at what is believed to be a turbulent time, when the planet was repeatedly pummeled by large ...