Emergence of a Habitable Planet

We address the first several hundred million years of Earth’s history. The Moonforming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over ∼1,000 yrs. As it cooled the Earth degassed its volatiles into the atmosphere. It took another ∼2 Myrs for the magma ocean to freeze at the surface. The cooling rate was determined by atmospheric thermal blanketing. Tidal heating by the new Moon was a major energy source to the magma ocean. After the mantle solidified geothermal heat became climatologically insignificant, which allowed the steam atmosphere to condense, and left behind a ∼100 bar, ∼500 K CO2 atmosphere. Thereafter cooling was governed by how quickly CO2 was removed from the atmosphere. If subduction were efficient this could have K. Zahnle ( ) NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035, USA e-mail: [email protected] N. Arndt LGCA, University Joseph Fourier, 1381 rue de la Piscine, 38401 Grenoble, France C. Cockell Planetary and Space Sciences Research Institute, Open University, Milton Keynes, MK7 6AA, UK A. Halliday Department of Earth Sciences, University of Oxford, Oxford, OX1 3PR, UK E. Nisbet Department of Geology, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK F. Selsis Ecole Normale Supérieure de Lyon, Centre de Recherche Astronomique de Lyon, 46 Allée d’Italie, 69364 Lyon, Cedex 07, France F. Selsis CNRS UMR 5574, Université de Lyon 1, Lyon, France N.H. Sleep Department of Geophysics, Stanford University, Stanford, CA 94305, USA