The Great Oxygenation Event (GOE) around 2.4 Ga might have been triggered by
cyanobacteria, which appeared 200 million years before. The appearance of oxygen
resulted in the loss the methane greenhouse. Although the origin of the sedimentary Mn
was once a big mystery, recent work has suggested that this deposit formed in the
aftermath of the Makganyene “Snowball Earth” event around 2.22 billion years ago
(Kirschvink et al., 2000, Kopp et al., 2005). Upon melting of the Snowball ice cover, the
buried seawater would have welled up along continental margins, fertilizing a bloom of
oxygen-releasing cyanobacteria that first oxidize and precipitate out the dissolved iron,
and finally the manganese (Kirschvink et al., 2000; Kopp et al., 2005). In addition,
peroxides accumulated in the ice during the long snowball episodes could contribute to
this (Liang et al., 2006).
Kirschvink, J. L., E. J. Gaidos, L.E. Bertani, N.J. Beukes, J. Gutzmer, L.N. and R.E.
Steinberger, (2000). Paleoproterozoic Snowball Earth: Extreme climatic and geochemical
global change and its biological consequences. Proc. Natl. Acad. Sci. USA 97(4): 14001405.
Kopp, R. E., J. L. Kirschvink, I.A. Hilburn and C.Z. Nash, (2005). The paleoproterozoic
snowball Earth: A climatic disaster triggered by the evolution of oxygenic photosynthesis,
Proc. Natl. Acad. Sci. USA 102: 11131-11136.
Liang, M. C., Hartman, H., Kopp, R. E., Kirschvink, J. L. and Yung, Y. L. (2006).
Production of hydrogen peroxide in the atmosphere of a Snowball Earth and the origin of
oxygenic photosynthesis. Proc. Natl. Acad. Sci. 103, 18896-18899.
Understanding how Earth has sustained surface liquid water throughout its history
remains a key challenge, given that the Sun’s luminosity was much lower in the past.
Here we show that with an atmospheric composition consistent with the most recent
constraints, the early Earth would have been significantly warmed by H2-N2 collision–
induced absorption. With two to three times the present-day atmospheric mass of N2 and
a H2 mixing ratio of 0.1, H2-N2 warming would be sufficient to raise global mean
surface temperatures above 0°C under 75% of present-day solar flux, with CO2 levels
only 2 to 25 times the present-day values. Depending on their time of emergence and
diversification, early methanogens may have caused global cooling via the conversion of
H2 and CO2 to CH4, with potentially observable consequences in the geological record.
The Archean Earth (3.8 to 2.5 billion years ago) was probably enshrouded by a
photochemical haze composed of fractal aggregate hydrocarbon aerosols. The fractal
structure of the aerosols would have had a strong effect on the radiative properties of the
haze. In this study, a fractal aggregate haze was found to be optically thick in the
ultraviolet wavelengths while remaining relatively transparent in the mid-visible
wavelengths. At an annual production rate of 1014 grams per year and an average
monomer radius of 50 nanometers, the haze would have provided a strong shield against
ultraviolet light while causing only minimal anti-greenhouse cooling.
Lavvas 2011