NASA Astrobiology Institute (NAI)

We are exploring the geological and geochemical record of ancient Earth for clues about the co-evolution of life and environment. We’re focusing on three events in Earth history: the apparent rise of atmospheric oxygen at 2.45 billion years ago, the establishment of life on land during the Cambrian (about 540 milliion years ago), and the greatest mass extinction of all time at the end of the Permian, 252 million years ago. We use a combination of computer modeling, field work, and laboratory analysis.

Our hypothesis concerning the evolution of atmospheric oxygen, based on analysis of existing data, has been published in two articles appearing in Nature and Science. We link the rise of oxygen to the establishment of large and thick continents and associated subaerial volcanoes at the end of the Archean.

Work on the evolution of terrestrial ecoystems has progressed well: we now have several well-characterized paleosols (ancient soils) from the the continental United States developed during the Cambrian “explosion” of biodiversity (in the marine realm); we’re addressing environmental and biotic change on land during this event. All soils exhibit extreme weathering depletion of major cations, perhaps consistent with the post-Snowball Earth supergreenhouse state of the Late Neoproterozoic and early Cambrian.

Finally, we’ve published two new papers on the Permian extinction and related anoxic ocean states, arguing that anoxia and the buildup of hydrogen sulfide might be more important than imagined for the end-Permian event and less important for the Proterozoic than envisioned. We have also established the biomarker distributions in a modern euxinic (H2S-rich) environment, learning that abundant green sulfur bacteria are not producing their characteristic biomarker isorenieratene, and that benthic forms of the purple sulfur bacteria produce okenone, in contradiction to recently published claims that okenone production is a planktonic PSB biomarker. This latter finding is especially important to our interpretation of biomarker distributions in ancient rocks.