Chemical Education Today
Reports from Other Journals
Nature: Our Atmosphere in the Year of Planet Earth by Sabine Heinhorst and Gordon C. Cannon
150
Phanerozoic
Proterozoic
0.5
Oldest fossils of eukaryotes Oldest cyanobacterial fossils Oxygenation of atmosphere
2.5
Archaean
Previously identified biomarkers for presence of cyanobacteria
4.0 ~4.6
Hadean
Since the International Union of Geological Sciences (IUGS) and UNESCO have declared 2007–2009 the Inter- Figure 1. The official logo of the national Year of Planet International Year of Planet Earth. The Earth (Figure 1), we red inner circle represents the solid Earth; would be remiss if we green indicates its biosphere, dark blue did not alert our read- its hydrosphere. The outer light blue circle ers to the Year of Planet represents its atmosphere. Courtesy IYPE Earth supplement to Secretariat. Nature [2008, 451, January 17, 257–303] that covers several aspects of climate change and its effect on society. We want to emphasize that the entire series of excellent articles and essays is worth reading and lends itself to classroom discussions and reflections on anthropogenic effects on global climate, challenges for society, and the need for sustainability measures in the years to come. Educators might also want to browse http://www.yearofplanetearth.org/ (accessed Nov 2008) for downloadable resource material related to various Earth science topics. Particularly relevant to the topic of this column is the article by L. R. Kump from Pennsylvania State University on the rise of oxygen in Earth’s atmosphere over geological time (pp 277–278). The author summarizes the existing evidence for “the great oxidation event” some 2.45 billion years ago, discusses likely geological and biological causes for the rise in atmospheric oxygen at the end of the Archaean, and points out questions that remain unanswered. One of these is the timing of this change in atmospheric composition (Figure 2). The oxygenic photosynthesis activity of cyanobacteria is widely believed to have been a major contributing factor. Prior research, however, had found molecular proxies for the presence of these microbes in rocks whose age predates the rise in atmospheric oxygen by several hundred million years and had therefore suggested a much earlier evolutionary origin of cyanobacteria. Recently, researchers from three Australian universities re-examined the same rocks that had been studied earlier. B. Rasmussen and colleagues report [2008, 455, October 23, 1101–1104] that the results they obtained using NanoSIMS (secondary ion probe mass spectrometry) (Figure 3), a relatively new analytical technique that detects trace elements with very high sensitivity (
