My team is conducting research on three critical intervals of environmental change whose evolutionary consequences are in large part responsible for the current state of Earths' biosphere:

(1) the Archean/Proterozoic transition (2.5 to 2 billion years ago), when large cratons stabilized, ice sheets waxed and waned, the oxidizing potential of the atmosphere and oceans increased markedly, bacteria with the capacity for aerobic metabolism radiated, and mitochondria-bearing eukaryotic microorganisms appear to have evolved; (2) the Proterozoic/Cambrian transition (800-509) million years ago, when supercontinents formed, broke apart, and reamalgamated, ice sheets repeatedly spread across the continents, global oxygen levels increased again, and large multicellular life emerged; and (3) the Permian-Triassic boundary (251 million years ago) when rapid and pronounced environmental changes nearly eliminated multicellular organisms from the planet, triggering the most comprehensive reorganization of animal life since the Cambrian explosion.

What is striking about these events is that they share a number of common features, despite being separated by large spans of time, and despite the vast differences in the environmental conditions and in the ecosystems prevalent at these times. This suggests that there may be general features governing the relationship between environmental change and major episodes of ecosystem evolution. By examining these general features of the Earth's past, we hope toprovide data and insights of direct relevance to understanding the development of planetary-scale ecosystems. Further, the new techniques and approaches that we are developing for probing the terrestrial rock record will be directly applicable to and necessary for the paleobiological and paleobiogeochemical investigation of ancient sedimentary rocks on other planets.

Laboratory/Facilities:
Our laboratory is centered around a VG Sector 54 mass spectrometer and a Micromass Isoprobe-T which are housed in a temperature controlled "clean room" equipped with laminar flow stations. The Sector 54 instrument is equipped with seven Faraday cups and an ion-counting Daly detector for small ion beams. The Isoprobe T is equipped with 9 Faraday collectors, an ion-counting Daly, and a WARP filter. U-Pb zircon analyses are performed using a mixed ²⁰⁵Pb-²³⁵U-²³³U spike, with total procedural blanks that are routinely 0.4-1.5 picograms for lead and less than 0.1 picograms for U. Using single collector ion-counting with peak jumping, we achieve high-precision analyses of samples with as little as 5-10 picograms of radiogenic Pb; at present, our minimum sample size is blank limited.

Nd and Sm analyses are routinely done in dynamic analysis mode with external reproducibility of isotope ratios over 10 years better than 20 ppm (2 sigma). La Jolla Nd analyses over the same period yield ¹⁴³Nd/¹⁴⁴Nd = 0.511854 ± 0.000009 (2 sigma) for ¹⁴⁴Nd = 1.5 X 10-11 amp analyses. Samarium is typically analyzed in static multicollector mode with precision better than 0.01% (2 sigma).

Courses Related to Astrobiology
Astrobiology 12.A34