Origin & Evolution of Life: November 2007

Researchers from NAI's University of Hawai'i Team and their colleagues have a new paper in Geobiology reviewing recent work on the climatic, geochemical, and ecological events that preceded animal fossils, considering their portent for metazoan evolution. They also consider recent published research on the nature and chronology of the earliest fossil record of metazoans, and on the molecular-based analysis that yielded dates older than the last 35 million years of the Precambrian for the appearance of major animal groups.

[Source: NAI Newsletter]

NAI's Astrobiology Drilling Program supported researchers in 2004 to obtain subsurface core samples from the Hamersley Basin in Western Australia. Those samples, representing the time just before the Great Oxidation Event, have been analyzed, and two research papers detailing the results (Anbar, et al. and Kaufman, et al.) appear in September 28, 2007 issue of Science. Both groups found unexpected, correlated changes that reveal the presence of small but significant amounts of O2 in the environment 2.5 billion years ago, ~50-100 milion years before the Great Oxidation Event, and a shift from lower O2 abundance prior to that time. [Source: NAI Newsletter]

Speaker: Ariel Anbar (Arizona State University)
Date/Time: Monday, November 5, 2007 11:00 AM PST

Abstract: Many lines of evidence point to a rapid rise of atmospheric O2 between 2.45 - 2.22 billion years ago (Ga), a transition often referred to as the Great Oxidation Event (GOE). The cause of the GOE is unknown. It could have been an immediate consequence of the evolution of oxygenic photosynthesis. Alternatively, O2 biogenesis may be ancient and the GOE a consequence of an abiotic shift in the balance of oxidants and reductants at the Earth's surface that crossed a critical threshold at that time. In the latter case, oxygenic photosynthesis could have evolved long before the GOE. This debate can be addressed by looking for evidence of localized or short-lived concentrations of O2 before 2.45 Ga.

Researchers from NAI's Carnegie Institution of Washington Team have a paper in Nature describing evidence that Earth's Mesoarchean atmosphere (3.2 and 2.8 Gya) possessed very low amounts oxygen. These findings contrast with prior claims that Earth's atmosphere underwent its first rise in oxygen during the Mesoarchean, and indicate that oxygen first rose above parts per million levels sometime between 2.45 and 2.4 billion years ago. [Source: NAI Newsletter]