WARC DISCOVERIES

Evidence that “iron-eating" bacteria existed on the early Earth two to three billion years ago

Extensive, iron-rich deposits called “Banded Iron Formations’ (BIFs) were deposited on Earth between 3.8 and 0.7 billion years ago and these rocks record times when massive amounts of iron was cycled through the marine sedimentary system to an extent not seen today. WARC researchers  Clark Johnson, Brian Beard, and Eric Roden have published in the journal Geochimica et Cosmochimica Acta iron isotope evidence that iron-reducing bacteria played a significant role in iron cycling in the largest BIFs, the famous 2.5 billion-year-old sequences in Australia and South Africa. Although iron-reducing bacteria are well-known in modern marine environments, establishing a timeline for development of this metabolism in the early part of Earth’s history is only just beginning. The earliest BIFs of 3.8 billion year age do not appear to have involved iron-reducing bacteria based on iron isotope data, raising the question of when this metabolism became established between 3.8 and 2.5 b.y. ago. WARC researchers will be pursuing this question with through further study.

Citation:
Johnson, CM, Beard, BL, Klein, C, Beukes, NJ, and Roden, EE (2008) Iron isotopes constrain biologic and abiologic processes in banded iron formation genesis. Geochimica et Cosmochimica Acta 72:151-169. A PDF copy of the paper can be found here.

Posted January 11, 2008