Impact hot spots on the cold surface of the early Earth

The cooling rates for a thin upper layer of impact-melted material on the surface of the growing Earth were calculated using the experimental data for convective heat transfer coefficient. The presence of an atmosphere on the Earth embryo leads to very high cooling rates of the surface layer of impact crater. We find that during Safronov's type of accretion more than 90% of the Earth's surface was below the freezing point of water and the blanketing effect of greenhouse gases was unable to maintain a global magma ocean on Earth. (C) 2002 Elsevier Science Ltd. All rights reserved.