Evolution of Earth’s Atmosphere
Earth’s atmosphere has a central role in keeping the environmental conditions on Earth suitable for life. When considering the evolution of the composition of the atmosphere, attention should be paid specifically to greenhouse gases and oxygen. The most important greenhouse gases are water vapor, carbon dioxide and methane. Atmospheric water vapor is always near its condensation temperature and cannot act as an independent climate forcer. Carbon dioxide and methane, in turn, are greenhouse gases, with a high potential for significant variations in their concentrations. For understanding Earth’s climate in the past, it is essential to estimate the concentration history of these two atmospheric components. Oxygen is highly reactive gas, which is in strong disequilibrium with minerals and rocks of the planetary surface. Direct analyses from atmospheric gases exist only for the last 800,000 years. For the earlier geological history, compositional estimates are derived from proxy variables and elemental cycle modeling. The proxy records and carbon cycle modeling indicate that Earth’s history is characterized by generally increasing carbon dioxide levels. In the past, higher contents of carbon dioxide were required to keep the planet from freezing as a result of the reduced power output from the faint young Sun. According to the standard solar model, immediately after the formation of the planet, the luminosity of the Sun was only 70% of the corresponding present-day value. The early atmosphere was anoxic, and as a result, the contents of methane in the atmosphere may have been several orders of magnitude higher compared to the contents in the modern atmosphere. About 2,400 Ma ago the atmosphere experienced a major shift from an anoxic to an oxic state, which may have been one of the most severe environmental changes ever having faced the planet. The most convincing evidence for the shift in the oxidation state is provided by the disappearance of mass independent sulfur isotope fractionation effects in sedimentary sulfur minerals.
KeywordsIsotopic Composition Atmospheric Oxygen Sulfur Isotope Sedimentary Organic Matter Early Atmosphere
- Holland HD (1978) The chemistry of the atmosphere and oceans. Wiley Interscience, New YorkGoogle Scholar
- Holland HD (1984) The chemical evolution of the atmosphere and oceans. Princeton University Press, PrincetonGoogle Scholar
- Karhu J (1993) Paleoproterozoic evolution of the carbon isotope ratios of sedimentary carbonates in the Fennoscandian Shield. Bull Geol Surv Finland 371:1–87Google Scholar
- Karhu J (1999) Carbon isotopes. In: Marshall CP, Fairbridge RW (eds) Encyclopedia of Geochemistry. Kluwer Academic Publishers, Dordrecht, pp 67–73Google Scholar
- Schidlowski M, Hayes JM, Kaplan IR (1983) Isotopic inference of ancient biochemistries: Carbon, sulfur, hydrogen and nitrogen. In: Schopf JW (ed) Earth’s earliest biosphere, its origin and evolution. Princeton Universtity Press, Princeton, pp 149–186Google Scholar