Research

Deploying a Maclane in-situ pump in the northeastern Pacific

My research focuses on  the interaction of the biological and geological worlds, particularly in using the sedimentary record of organic materials to understand how the Earth works. Since the time of Charles Darwin, we have known that our physical environment helps to shape life through the process of evolution. More recently, we have come to understand that the guidance is reciprocal, and that biology also influences the evolution of the Earth (the oxygen we breath today is present only because of photosynthesis by plants and bacteria). One of the goals of my research is to understand the details of this complicated relationship. Several specific projects are described the links on your right.

In general, the objects of our study are the waxy, organic molecules that are produced by living organisms and eventually buried and preserved in sediments. Known generically as lipids, these molecules are the raw materials that eventually produce petroleum and natural gas, as well as record a rich history of life over the past ~3 billion years. Because they are so well preserved, lipids are often called “molecular fossils” and can be used to study the origins and evolution of life. As an example, we have used these molecular fossils to understand environmental conditions that prevailed during one of the Proterozic low-latitude glaciations, which have become known as "Snowball Earth" events. We are also interested in how these molecules are produced, cycled, buried, and preserved in the modern environment, which forms a key link in the modern carbon cycle; and how they are converted into hydrocarbons, that form the basis for our energy economy.

The tools of my research are those of the organic chemist, primarily gas chromatography and mass spectrometry. These instruments allow us to separate individual organic compounds from complex samples, to identify the structures of those compounds, and to measure their abundance and stable-isotopic composition. We use the isotopes of carbon, hydrogen, nitrogen and sulfur as a sort of chemical fingerprint to follow organic molecules through the geologic environment. Much of our current work is focused on understanding the biogeochemical controls over the distribution of hydrogen (2H and 1H) and sulfur (34S, 33S, 32S) isotopes in organic materials, with the goal of eventually using these tracers to understand the ancient life and environments. We are also measuring molecules with multiple rare isotope substitutions (e.g., 13CH32H), with applications to both modern greenhouse gas emissions and understanding the origins of natural gas.


Copyright 2015 by Alex Sessions. All rights reserved.