ABSTRACT
There is a very strong connection between life forms on Earth and the nature of Earth’s atmosphere and climate, which determine its suitability for life. As proposed by James Lovelock, a renowned British environmental chemist, this forms the basis of the Gaia hypothesis, which contends that the atmospheric O2/CO2 balance established and maintained by organisms determines and stabilizes Earth’s climate and other environmental conditions. Living organisms have had a profound infl uence on the atmosphere in the past. The most massive of the changes caused were those arising from photosynthesis, which utilizes solar energy, hν, to produce biomass, {CH2O}, and molecular oxygen, O2:
CO2 + H2O + hν → {CH2O} + O2(g) (9.1.1) This process converted Earth’s atmosphere from a chemically reducing to a
chemically oxidizing state and precipitated enormous deposits of insoluble oxidized iron:
4Fe2+ + O2 + 4H2O → 2Fe2O3 + 8H+ (9.1.2) In addition to providing O2 that most nonphotosynthetic organisms use for res-
piration, the photosynthetically released oxygen formed stratospheric ozone (O3), which absorbs damaging ultraviolet radiation from the sun, enabling living organisms to move from water onto land where they are directly exposed to sunlight.
