Earth and life: A dance through time – the Crafoord Academy Lecture 2015 with Andrew H. Knoll, Harvard University, Cambridge, MA, USA.
Earth and life: A dance through time
Andrew H. Knoll, Harvard University, Cambridge, MA, USA. Introduction by Daniel Conley, Lund University and Stefan Bengtson, the Swedish Museum of Natural History, Stockholm.
Earth is a planet that records its own history, including an interwoven narrative of evolution and environmental change through time. The interplay between Earth and life plays out on many scales, none more dramatic than the largest – planetary in extent and billions of years long. Fossils of shells, bones, tracks and trails record a history of animal evolution early 600 million years in duration. Earth, however, is some four and a half billion years old – what kinds of organisms characterized our planet’s youth and middle age? And how do we establish the nature of life and environments on the early Earth? Comparative biology suggests that the deep history of life is microbial, and over the past three decades paleontologists have discovered a rich record of ancient microorganisms in rocks that long predate the earliest evidence of animals.
Rock chemistry, in turn, indicates that the first billion years of microbial evolution played out on a planet without oxygen. 2400 million years ago, the initial accumulation of oxygen in the atmosphere and surface oceans opened a new chapter in Earth history, one in which an expanding diversity of life thrived in oceans with moderate oxygen at the surface, but oxygen-free waters below. Only much later did our familiar world of abundant oxygen and conspicuous animals take shape, adding complexity to ecosystems still governed by microbial metabolisms that originated on the early Earth.
Andrew H. Knoll is the Fisher Professor of Natural History at Harvard University. He is best known for his work on early life and environments, but additionally has longstanding interests in biomineralization, paleobotany, plankton evolution, and mass extinction. Knoll also serves on the science team for NASA’s MER mission to Mars. Honors include membership in the US National Academy of Sciences and foreign membership in the Royal Society of London.