↑ Knoll, Andrew H. 2004. Life on a young planet: the first three billion years of evolution on Earth. Princeton, N.J. ISBN 0-691-12029-3
↑ For a description of the method used to establish this date, see J. William Schopf 1999. Cradle of Life: the discovery of Earth's earliest fossils. Princeton U. Press (pages 87-89 and figure 3.9). The remarkable precision was possible because the fossils were sandwiched between lava flows that could be precisely dated from embedded zircon crystals.
