A Photobiological History of Earth

  • Charles S. Cockell


Ultraviolet radiation has been a ubiquitous physical stressor since the origin of the first microbial ecosystems during the Archean era (3.9–2.5 Ga [billion years] ago). Although the UV radiation that reaches the surface of the Earth spatially and temporally depends on many factors (Xenopoulos and Schindler, Chapter 2, this volume), during the history of life on Earth four distinct periods of photobiological history can be recognized (Cockell and Knowland 1999). First, the period during which UV radiation influenced chemistry on prebiotic Earth during the Hadean era (>3.9 Ga ago) dominated by the involvement of UV radiation in organic complexification as well as the deleterious effects it may have had on exposed prebiotic molecules. Because this does not involve ecosystems or biological organisms per se, it is not discussed in detail here, although discussions on the role of UV radiation on prebiotic Earth can be found elsewhere (Sagan 1973; Kolb, Dworkin and Miller 1994; Cleaves and Miller 1998; Bernstein et al. 1999; Cockell and Knowland 1999).


Photic Zone Supernova Explosion Origin Life Screen Compound Column Abundance 
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