Earth's Early Atmosphere, Biosphere, Lithosphere, and Hydrosphere

Reconstructions of ancient ecological interactions rely upon information found in rocks deposited at Earth's surface billions of years ago. Geologic and geochemical evidences of the nature of early Earth are widely dispersed in isolated outcrops across the globe and are imperfectly preserved. In addition to the impediments to understanding imposed by a fragmentary historical record, knowledge must be gained from studying modern environments in order to interpret evidence gleaned from Earth's oldest rocks. The application of data measured on modern samples to decipher clues hidden in ancient rocks necessitates extrapolating several billion years in time, a problematical exercise at best. There is an inevitable logical circularity in accepting the present as the key to the past: But, what other benchmark does one have? This presentation will explain how geological and geochemical evidence is used to constrain hypotheses for the evolution of Earth's atmosphere, biosphere, hydrosphere, and lithosphere, prior to 2.5 billion years ago.