If we apply the same model of a condensible CO2/H20 volatile inventory to the early Earth, we find that for generally accepted values of the Faint Young Sun solar constant S >0.7, then a relatively thick CO2 atmosphere is stable. Essentially the entire available CO2 inventory is in the atmosphere, except for a fair volume dissolved in the oceans. The climate is hot (220 Centigrade at the poles!), and life as we know it is impossible. However, the hot acid CO2-satturated oceans do not evaporate, and the CO2 reacts rapidly with rock to form inorganic carbonate, consuming the CO2 and reducing Earth to a more clement planet with only ~0.5 bars CO2 (still fatal to higher life, but ideal for extremophile organisms)

However, if the Faint Young Sun were just a hint fainter, or if the albedo of the shiny icecaps was a little stronger than the greenhouse effect of the atmospheric gases, then the early Earth would also have been an iceworld with very unusual properties...

For S=0.68, the atmosphere collapses on Earth, like on White Mars, although not so completely. A mere 263 mbar of CO2 enters the atmosphere (although about total atmospheric pressure would be about 1 bar, with the remainder of the atmosphere consisting mostly of Nitrogen). The mean global temperature would be 257 K (-15 Centigrade), with equatorial mean temperature a very pleasant 307 K (+35 C). The poles would average frighteningly cold 180 K (-87 C), with solid CO2 icecaps twenty times the existing polar ice volume, extending down to lattitudes where CO2 began to boil directly into the atmosphere from the solid state.

Interestingly, in temperate regions in the oceans and in the crust, at depths of 100m or more, both liquid CO2 and water would be stable. Excess Co2 would exist for solution in the water and so immiscible phases of CO2 and would coexist. In these circumstances, which can be simulated in the laboratory, one liquid forms blobs in the other, like oil and water that have been shaken up. The CO2 tends to sink to the bottom, because it is denser, but bubbles of one liquid will remain in the other for some considerable time.

This intimate mixture of water and liquid CO2 provides an incredibly unique environment in which cellular life could have originated.
 

      Created: May 2002
      Last modified: May 2002
      Authorised by:  Head, Earth Sciences

      Maintained by: Nick Hoffman