title: Comment on "A hydrogen-rich early Earth atmosphere".
abstract: Tian et al. (Reports, 13 May 2005, p. 1014) proposed a hydrogen-rich early atmosphere with slow hydrogen escape from a cold thermosphere. However, their model neglects the ultraviolet absorption of all gases other than H2. The model also neglects Earth's magnetic field, which affects the temperature and density of ions and promotes nonthermal escape of neutral hydrogen.
authors.affiliation: Department of Earth Sciences, University of Bristol, Queen's Road, Bristol BS8 1RJ, UK.
authors.forename: David C
authors.initials: DC
authors.lastname: Catling
mesh_terms: D001272:Atmosphere; D002245:Carbon Dioxide; D018534:Earth, Planet; D019418:Evolution, Chemical; D006371:Helium; D006859:Hydrogen; D009930:Organic Chemicals / Q000737:chemistry; D013696:Temperature
chemical_list: D009930:Organic Chemicals; D002245:Carbon Dioxide; D006371:Helium; D006859:Hydrogen