Warming early Earth and Mars
- Pennsylvania State Univ., University Park, PA (United States)
Sagan and Chyba, in their article on page 1217 of this issue, have revived an old debate about how liquid water was maintained on early Earth and Mars despite a solar luminosity 25 to 30% lower than that at present. A theory that has been popular for some time is that greatly elevated concentrations of atmospheric COD produced by the action of the carbonate-silicate cycle, provided enough of a greenhouse effect to warm early Earth. However, Rye et al. have placed geochemical constraints on early atmospheric CO{sub 2} abundances that fall well below the levels needed to warm the surface. These constraints are based on the absence of siderite (FeCO{sub 3}) in ancient soil profiles-a negative and, hence, rather weak form of evidence- and apply to the time period 2.2 to 2.8 billion years ago, when Earth was already middle aged. Nonetheless, the soil data provide some indication that atmospheric CO{sub 2} levels may have been lower than previously thought. An even more serious problem arises if one tries to keep early Mars warm with CO{sub 2}. Model calculations predict that CO{sub 2} clouds would form on Mars in the upper troposphere, reducing the lapse rate and severely limiting the amount of surface warming. A suggestion that CO{sub 2} clouds may have warmed the planet radiatively has yet to be borne out by detailed calculations. 26 refs.
- OSTI ID:
- 530884
- Journal Information:
- Science, Vol. 276, Issue 5316; Other Information: PBD: 23 May 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
MECA Conference on Mars: the Evolution of Its Climate and Atmosphere, Washington, DC, July 18, 19, 1986, Proceedings
Application of laser induced breakdown spectroscopy (LIBS) to Mars polar exploration : LIBS analysis of water ice and water ice/soil mixtures