David Catling, Ph.D.

Professor, Department of Earth and Space Sciences, University of Washington
David Catling’s website
Portrait photo of David Catling

SCOL Project: Constraining the Environment for Life’s Origin and the Spread of Early Life

Life emerged from Earth’s early environment, so explanations for the origin of life need to be consistent with our understanding of the conditions that prevailed back then. To determine these conditions, we will run computer simulations, collect and analyze rocks that tell us about the ancient environment, and conduct experiments to examine a hypothesis for how organic molecules were made before life began.

Our first major goal is to estimate environmental parameters, such as surface temperature, seawater pH, atmospheric pressure and levels of atmospheric gases (carbon dioxide, nitrogen, hydrogen and methane), as well as the uncertainty of each parameter. We will analyze pH-dependent concentrations of rare earth elements in sedimentary rocks to tell us how seawater pH changed since about four billion years ago. Concentrations of atmospheric methane and hydrogen are related to the process by which heavy and light xenon atoms (i.e., isotopes) were separated when hydrogen escaped from the early Earth into space and preferentially removed light xenon atoms. Measurements of existing xenon isotopes in ancient rocks will allow us to deduce ancient levels of methane and hydrogen. We will also determine hydrogen level limits by examining how certain observed minerals should have otherwise decomposed in the presence of too much hydrogen. Additionally, we will use air-pressure-dependent grain size distributions in fossil sand dunes to estimate air pressure on the early Earth, giving us insight into past atmospheric nitrogen levels.

Our final task will be to examine a leading concept, namely, that hydrogen cyanide (HCN) was a crucial molecule that triggered the natural synthesis of organic compounds used in life’s origin. We will determine the rate of HCN production in the atmosphere and HCN’s environmental fate. Results will provide the best estimates of environmental conditions for the origin of life available and a new assessment of the plausibility of HCN as a molecule that led to the origin of life.

David Catling is a professor in the Department of Earth and Space Sciences and the cross-campus Astrobiology Program at the University of Washington, Seattle. After completing a doctor of philosophy in atmospheric, oceanic and planetary physics at the University of Oxford in 1994, he was a researcher in planetary science and astrobiology at NASAs Ames Research Center in California from 1995–2001. In 2001, he joined the faculty at the University of Washington. Subsequently, he was awarded a European Union Marie Curie Chair for 2005–2008 at the University of Bristol, England, after which he returned to Seattle. Catling’s research interests concern the geochemical evolution of planets, which includes their atmospheres, surfaces and potential for life. As part of his research, he has been involved in the exploration of Mars and was on the team of scientists responsible for NASA’s 2008 successful Mars Phoenix Lander. His work dealing with the Earth focuses on understanding how the environment changed over the planet’s entire 4.5 billion year history by combining expertise in biogeochemistry and atmospheric composition (addressed through numerical simulations and proxy data), atmospheric radiation and climate, atmospheric chemistry and aqueous geochemistry. He has written books, including Astrobiology: A Very Short Introduction (Oxford University Press, 2013), for a general audience and co-authored a research-level monograph on the origin and evolution of atmospheres: Atmospheric Evolution on Inhabited and Lifeless Worlds (Cambridge University Press, 2017).

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