Despite the faintness of the young Sun, the early Earth appears to have been warm, or perhaps even hot. Taken at face value, oxygen and silicon isotopes in ancient cherts imply a mean surface temperature of 70(±15)°C at 3.3 Ga1,2. Ancient carbonates also yield high Precambrian surface temperatures3, as does a recently published analysis of the thermal stability of proteins which are inferred to be ancient4. This evidence for hot early surface temperatures must be weighed against the previously mentioned dimness of the young Sun, as well as geomorphic evidence for glaciation at 2.9 Ga, 2.4 Ga, and 0.6-0.7 Ga. Climate models with high CO2 and CH4 concentrations can potentially explain hot climates, but can they explain climates that transition from hot to cold, and back again, multiple times? Such models must also account for the well documented correlation between the rise of O2 at 2.4 Ga and the Paleoproterozoic glaciations which occurred at that same time. Models that do5 and do not6 rely on changes in seawater oxygen isotopic composition will be discussed.
References:
1 Knauth and Lowe, GSA Bull., 2003
2 Robert and Chaussidon, Nature, 2006
3 Shields and Veizer, G3, 2002
4 Gaucher et al., Nature, 2008
5 Kasting et al., EPSL, 2006
6 Came et al., Nature, 2007
Getting Under Europa’s Skin
Tracing Formation and Evolution of Outer Solar System Bodies Through Stable Isotopes and Noble Gas Abundances
Photosynthesis, a Planetary Revolution
Xenon: King of the Gases
NAI
