People: Astrobiology Postdocs

Julien Foriel
Earth & Space Sciences

My primary interest is the study of the oxidation state of Earth surface, how it evolved from 4 billion years ago in response to geological or biological forcing and how it in turn influenced biological evolution.

I am very keen on addressing such issues by developing novel analytical techniques and new experimental approaches. During my PhD (IPGP, Paris, France, 2004), I used synchrotron radiations to try and characterize the composition of 3.5 billion-years-old seawater and to image the sulfur redox state in fossilized bacteria.

As an Astrobiology postdoc at the University of Washington, I have setup sulfur isotope analysis and I am not working on a protocol for selenium isotopes analysis.

Sulfur isotopes can be used as tracers of the biogeochemical cycle of sulfur and help understanding the gradual oxygenation of Earth atmosphere and oceans as well as the evolution of the biosphere over the last 3.5 billion years. They can also shed light on the processes (such as ocean anoxia) involved in Phanerozoic mass extinction events such as the Permian-Triassic extinction, about 250 million years ago (see picture).

Selenium, as a chemical analog of sulfur, promises to be a powerful tool for the study of the oxidation of the atmosphere and oceans, particularly during the interval in between the two Great Oxidation Events (around 2.5 and 0.7 billion years ago), where precise constraints on oxygen levels are lacking. Se isotopes in rocks can currently only be analyzed by a (small) handful of labs in the world and we are racing to join them, it is a difficult experimental challenge but the prospects are indeed exciting!

Standing on the Permian-Triassic Boundary at Opal Creek, Canada.