Archives

Geobiology: April 2012


Geological background of the samples analyzed in this study. Panel A shows the geological map at Marble Bar and the location of the ABDP-1 drill core. Panel B shows the simplified stratigraphic column of the lower part of the Pilbara Supergroup, with ages constrained by zircon U-Pb geochronology.

Astrobiologists from NAI's team at the University of Wisconsin, Madison have recently published a study of drill cores obtained through the NAI-funded Archean Biosphere Drilling Project which sampled the 3.4 billion year old Apex Basalt from the Pilbara Craton in Western Australia. Their innovative approach directly dates oxidation products of the ancient rock, and they show that oxidation occurred in the Phanerozoic during deep weathering. Their results indicate that oxidation of the Apex Basalt did not occur in the Archean, and therefore cannot be used to infer an oxygenated atmosphere at that time. Their paper appears in Earth and Planetary Science Letters.

Reading the Rocks

For more than a decade, scientists have dismissed claims that examining carbon-rich rocks could yield clues to the atmospheric and oceanic conditions on Earth hundreds of millions of years ago. Now, however, researchers including members of NAI's MIT Team are challenging that belief, and suggesting that data gleaned from the rocks sheds light on how changes in the atmosphere and oceans helped set the stage for the emergence of animal life.

In one of the largest studies of its kind, described in the March 14 issue of Nature, a group of researchers led by David Johnston, Assistant Professor of Earth and Planetary Sciences, analyzed hundreds of samples of carbon-rich rock collected from sites in Canada, Mongolia, and Namibia. Their findings show that carbon isotope records from the mid-Neoproterozoic era -- between 717 million and 635 million years ago -- can be "read" as a faithful snapshot of the surface carbon cycle.