Elizabeth Bell, Ph.D.

University of California, Berkeley
Past SCOL Member

Education: University of California, Los Angeles, Ph.D. Geochemistry
Institution: University of California, Los Angeles, Earth and Space Sciences (laboratory of Mark Harrison)

SCOL Project: A Search for Isotopic Traces of Life in 4.0 to 4.4-Billion-Year-Old Minerals

Because Earth’s surface is continually scoured by water and other agents of erosion, our geologic record becomes increasingly sparse with age. Although the planet is over 4.5 billion years (Ga) old, rocks older than 4 Ga are currently unknown. This makes the earliest history of Earth, and any possible biosphere older than 4 billion years, largely inaccessible.

However, tiny grains of the mineral zircon (approximately the width of a human hair) from the Jack Hills in Western Australia range as old as 4.4 Ga, constituting the oldest known materials on the planet. These zircons contain abundant inclusions of earlier minerals, some of them carbon-bearing, that were enclosed in the zircon during its formation.

Since biologically-derived carbon tends to have characteristically low ratios of the isotope C-13 compared to C-12, carbon isotope ratios can be proxies for the presence of life even when direct fossils are not available. Bell intends to analyze a significant number of carbon-bearing inclusions in Jack Hills zircons in order to constrain the over-4-Ga carbon isotope record and determine whether it is consistent with the presence of life. This would constitute the oldest known evidence of life on Earth.

