E.A. Bell et al/PNAS 2015
New evidence suggests that life on Earth arose before 4.1 billion years ago, 300 million years earlier than previous estimates.
The oldest known fossils date back to around 3.5 billion years ago, so scientists use other clues in the search for early signs of life (SN: 2/8/14, p. 16). Life-forms preferentially stockpile carbon-12 in their cells, so any ancient substance enriched with carbon-12 could have a biological origin.
Researchers in California report the discovery of a 4.1-billion-year-old zircon crystal containing a carbon-12–laden impurity. Ancient carbon-containing zircons from this period are extremely rare — only around one in 10,000 crystals — so the finding will be difficult to confirm, the researchers note online October 19 in the Proceedings of the National Academy of Sciences.