Faint young sun

The CO2 content of the planetary atmosphere plays a vital role. A relatively high CO2 partial pressure was certainly an important precondition for solving the problem of the faint, young sun . It is assumed that the sun was much cooler four billion... 

The third reason for inferring a more C02-rich atmosphere in the past arises from what has become known as the "faint young sun paradox." This was first articulated by Sagan and Mullen (1972) who argued from solar models that in the early Archaean, the sun, as a relatively young star, would have had a 25-30% lower luminosity than it does now. This reduced luminosity, it is argued, would have led to much lower surface temperatures on Earth that at present, and a frozen Earth until about 2.0 Ga ago. The paradox arises because the Earth s oldest known sediments from the > Ga Isua greenstone belt are clearly water-lain and show no evidence of a frozen Earth (Fedo et al., 2001). 

FIGURE 5.15 Changing C02 levels in the Earth s atmosphere over time expressed as partial pressure of C02. The grey shaded area is the range of concentrations required to compensate for the faint young sun (after Kasting, 1993). The other data points shown are discussed in the text. 

Figure 5.15 also shows that these data confirm what has already been discussed, that estimates of C02 levels in the Archaean are lower than those required to compensate for the faint young sun and an additional greenhouse gas is required. This additional gas was most probably methane. 

Ever since the faint young sun problem was identified by Sagan and Mullen (1972) there... 

An important question related to the evolution of the Earth s climate is the so-called faint young sun paradox . Like other stars, the Sun evolves with time, so that the radiative energy it provides was probably 25-30% smaller 4 billion years ago than it is today. In spite of the small... 

The pressure and temperature of the Earth has been so constant that it has created its own scientific puzzle the Faint Young Sun Paradox. Carl Sagan and colleagues pointed out that the equations of stellar evolution show that our sun heats up over time (as accounted for by Eric Chaisson s energy rate density). Four billion years ago the sun gave out only two-thirds the light and heat that it does today. Under that faint sunlight, the oceans should have frozen completely, but the oceans liquid flow is clear from the rocks. So what warmed the oceans ... 

Kasting, J.F. (2000) iLong-term stability of Earth s climate the faint young Sun problem revisited , in Proceedings of the IGBP Workshop on Geosphere-Biosphere Interactions and Climate, Vatican City in press. 

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