About 0.73 Ga, Earth underwent severe glaciations that eliminated much of life. The Cryogenian (Greek; ice + birth) period was initiated by several conditions. [1] The breakup of the supercontinent Rodinia exposed organic matter to anaerobic respiration, creating an atmosphere in which the major greenhouse gas was methane (CH₄). Atmospheric CH₄, in contrast with CO₂, reacts with O₂ and is not buffered by a massive ocean reservoir; therefore, atmospheric CH₄ levels decreased rapidly once continental movements diminished and less organic matter was exposed. As CH₄ declined, Earth cooled. Cooler temperatures inhibited biological production of CH₄, accelerating the cooling. Ice appeared on the land masses near the equator, increasing the reflectance of solar energy (a phenomenon called albedo) and decreasing the solar energy retained at Earth’s surface. Temperatures sank until even some equatorial oceans were covered with ice. [2]

Recovery from these cold conditions depended on the buildup of atmospheric CO₂ levels through volcanic emissions of CO₂ and low-temperature inhibition of processes that deplete atmospheric CO₂, namely, silicate rock weathering and photosynthesis. Atmospheric CO₂ concentrations reached as high as 1.2% before the ice began to crack, exposing bare ground and open water, decreasing albedo, and creating a cascade of events that warmed the planet. [3]

This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.

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