Earth’s Earliest Life Written in Stone
Reconstructing Earth Life's Deep History and What It Suggests About Life Elsewhere in the Universe
Earth records its own history, encrypted in sedimentary rocks laid down one bed upon another through time. For nearly two hundred years, paleontologists have mined this archive for the fossils of plants and animals. We now know, however, that this record of shells and bones and leaves and wood captures only the last fifteen percent of life’s evolutionary history. In fact, life has been part of the Earth’s surface for most of the planet’s history, and for most of this time life was exclusively microbial.
How do we discover and interpret geological signatures of early microorganisms and the world they inhabited? Laboratory study of samples from as far afield as the Arctic, Siberia and Australia reveal microfossils, sometimes remarkably well preserved, that document the deep history of photosynthetic bacteria and, later, eukaryotic microorganisms. Chemical signatures in the same rocks record other bacteria and archaeons that cycled carbon, nitrogen and sulfur through ancient ecosystems. Other chemical details help us to reconstruct Earth’s environmental history, showing that life existed for a billion years or more before oxygen began to accumulate in the atmosphere and ocean.
Everything we know about life in the universe is from what can be found on the Earth in the geological record and in the living biota. At a time when perennial musings about life elsewhere are being reframed in terms of telescopes and planetary spacecraft, how does Earth’s record guide – and possibly limit – exploration for life in other parts of our solar system or beyond? Earth’s early biological record has informed the exploration of sedimentary rocks on Mars, guiding the search for ancient life on a planetary neighbor that probably does not harbor living organisms today. What aspects of life as we know it are likely to be universal, and in what ways might alien life depart from our terrestrial experience? In the absence of a second example of life, we cannot answer such questions, but continuing discussion will play an important role in guiding exploration on the search for life in our solar system and on the planets orbiting distant stars.
About the Speaker
Andrew H. Knoll is the Fisher Professor of Natural History at Harvard University. Previously he has served Harvard as Associate Dean of the Faculty of Arts and Sciences; Chair of the Department of Organismic and Evolutionary Biology, Professor of Biology and Professor of Earth and Planetary Sciences. Andy came to Harvard as Associate Professor of Biology in 1982, after five years on the faculty of Oberlin College. Andy also serves as a member of the science team for NASA’s MER mission to Mars.
Andy's research focuses on the early evolution of life, Earth’s environmental history, and, especially, the interconnections between the two. His research combines extensive fieldwork, paleontological discovery and geochemical analysis aimed at understanding the history of oxygen in the atmosphere and oceans.
Andy's honors include the Walcott and Thompson medals of the National Academy of Sciences, the Oparin Medal of the International Society for the Study of the Origins of Life, the Phi Beta Kappa Book Award in Science (for his 2003 book Life on a Young Planet), the Moore Medal of the Society for Sedimentary Geology, the Paleontological Society Medal, and the Wollaston Medal of the Geological Society of London.
He is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, the American Philosophical Society, a Foreign Member of the Royal Society of London, and has an Honorary Fellowship in the European Union of Geosciences.
Andy earned a BA in Geology from Lehigh University and a PhD in Geology from Harvard in 1977.