Scientists with NASA’s Astrobiology Institute (NAI) have discovered fossilized remnants of microbial mats that developed on land between 2.6 billion and 2.7 billion years ago in the Eastern Transvaal district of South Africa. This significant discovery presents the strongest evidence to date that life on land occurred at a much earlier stage in Earth’s history than was previously believed by most scientists. It also suggests that an ozone shield and an oxygen-rich atmosphere existed on Earth 2.6 billion years ago, both necessary conditions for life on land to emerge. The results are reported in the Nov. 30 issue of Nature magazine.