Figure 14-69. Some major events that are believed to have occurred during the evolution of living organisms on Earth.

Figure 14-69Some major events that are believed to have occurred during the evolution of living organisms on Earth

With the evolution of the membrane-based process of photosynthesis, organisms could make their own organic molecules from CO2 gas. As explained in the text, the delay of more than 109 years between the appearance of bacteria that split water and released O2 during photosynthesis and the accumulation of high levels of O2 in the atmosphere is thought to be due to the initial reaction of the oxygen with abundant ferrous iron (Fe2+) dissolved in the early oceans. Only when the iron was used up would oxygen have started to accumulate in the atmosphere. In response to the rising levels of oxygen in the atmosphere, nonphotosynthetic oxygen-using organisms appeared, and the concentration of oxygen in the atmosphere leveled out.

From: The Evolution of Electron-Transport Chains

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.