The big questions of how the Earth and Moon formed and first developed have, for many years, been at the borderline of tractability because of what appears to be an almost complete obliteration of any physical, chemical, or isotopic record of the first 500 million years of Earth history. We do know that in the first 200 million years the Earth acquired a core, a mantle, perhaps a primitive crust, and a hydrosphere and an atmosphere. It also became patently clear in the mid-1980s that the origins of the Earth and its Moon were inextricably intertwined.
Recently, various unrelated research efforts have provided exciting new lines of evidence that bear directly on these issues. The breakthroughs have come mainly with advances in simulations of the dynamics of planetary accretion, isotopic chronometers for the timescales of early solar system processes, noble gas constraints on the formation of the atmosphere, and melting experiments at previously unattainable pressures and temperatures. With this backdrop, scientists met last December to discuss their findings at a conference on “The Origin of the Earth and the Moon,” organized by the Geochemical Society and the Lunar and Planetary Institute.