Faint Young Sun - No Paradox
The faint young sun paradox is no paradox, according to a recent paper in Nature.
The faint young sun paradox is that the earth didn't freeze over when the sun was weaker at the time when the oceans formed. Earth's climate has been fairly constant during the approx. 4.6 billion years of earth's existence, despite the fact that radiation from the Sun is believed to have increased by 25-30 percent over that time.
Professor Minik Rosing, from the Natural History Museum of Denmark, and Christian Bjerrum, from the Department of Geography and Geology at University of Copenhagen, together with American colleagues from Stanford University in California claim that there is no paradox.
What kept the earth's oceans from freezing over?
Scientists have theorized for years that high concentrations of greenhouse gases could have helped Earth avoid global freezing in its youth by allowing the atmosphere to retain more heat than it lost.
How Carbon Dioxide Kept Earth From Being Mars
The new paper shows that ancient GHG levels were far too low to have this effect:
It has been inferred that the greenhouse effect of atmospheric CO2 and/or CH4 compensated for the lower solar luminosity and dictated an Archaean climate in which liquid water was stable in the hydrosphere. Here we demonstrate, however, that the mineralogy of Archaean sediments, particularly the ubiquitous presence of mixed-valence Fe(II–III) oxides (magnetite) in banded iron formations is inconsistent with such high concentrations of greenhouse gases and the metabolic constraints of extant methanogens.
The authors suggest that a combination of low albedo from lack of clouds and a considerably smaller continental land area combined to keep the earth warm enough to keep the water above freezing point. The lack of clouds is explained as being due to a lack of seeding chemicals from plants and algae which did not then exist.
The new model of an early earth and a faint sun does not require the presence of GHGs to explain the lack of freezing. In the absence of an extreme early CO2 level, the CO2 levels throughout earth's history become more moderate in range. This may place a greater emphasis on current CO2 trends as being abnormal.
Minik T. Rosing, Dennis K. Bird, Norman H. Sleep, Christian J. Bjerrum. "No climate paradox under the faint early Sun." Nature, 2010; 464 (7289): 744 DOI: 10.1038/nature08955
