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Research

I am a geologist and geochronologist working to resolve chronological questions involving human biological and behavioral evolution with the ⁴⁰Ar/³⁹Ar method. To do this, we measure isotopes of argon in crystals found in volcanic ashes that are interbedded with fossils and artifacts. I do most of my labwork at the Berkeley Geochronology Center, but I also use Steve Shackley's Berkeley Archaeological XRF Lab. I am working on several projects, some of which are outlined here.

⁴⁰Ar/³⁹Ar geochronology of Gademotta and Kulkuletti, Ethiopia
Gademotta and Kulkuletti are two Middle Stone Age (MSA) sites that were first excavated by a team led by Fred Wendorf in the 1970s. Initial K-Ar geochronology was done by Paul Damon and published by Wendorf et al., 1975. This work indicated that the MSA originated prior to 181 thousand years ago (ka), much earlier than was previously believed. However, since subsequent K-Ar work gave inconsistent results, we are reassessing the geochronology here using the ⁴⁰Ar/³⁹Ar method, which has eliminated many problems associated with K-Ar geochronology. I presented preliminary results at the Geological Society of America conference in 2007 (abstract), but ages have since been revised. More information will be available soon.

Geochronology at Melka Kunture, Ethiopia
Melka Kunture is located on the banks of the Awash River in Ethiopia and is particularly interesting because the area was inhabited during all major archaeological periods from the Oldowan through the Late Stone Age. I am working with the Italian Mission to Melka Kunture to obtain ⁴⁰Ar/³⁹Ar age constraints on the paleontology and archaeology found there.

⁴⁰Ar/³⁹Ar dating of volcanic glasses
Another area of interest involves understanding the systematics of applying the ⁴⁰Ar/³⁹Ar method to volcanic glasses. It seems that when glass interacts with groundwater, it often experiences potassium and/or argon mobility, which can affect the apparent ⁴⁰Ar/³⁹Ar age. Additionally, it is possible that argon in parts of the obsidian flow does not have time to equilibrate with the atmosphere prior to cooling. Although use of isochron ages rather than plateau ages eliminates this problem, we are looking into it as a possible explanation for sub-atmospheric initial ⁴⁰Ar/³⁶Ar values. I presented some of this work at the American Geophysical Union conference in 2007 (abstract).

Other Projects
I am also involved in field and lab work for several other paleontological and archaeological projects, including the Middle Awash and Moche Borago projects in Ethiopia, as well as the Tanzania International Paleoanthropological Research Project.