Oxygen and Evolution

13 May 2010

At www.physorg.com/print192714427.html - the journal Astrobiology has a paper that suggests the evolution of complex life forms may have had a kickstart a couple of billion years ago when geological events caused large quantities of phosphorous to wash into the oceans. In turn, this caused vast algal blooms that pumped extra oxygen into the environment which allowed larger more complex organisms to thrive. Phosphate rocks formed sporadically during geological time - and at the points when they appear, it is claimed, they seem to coincide with major global bio-geochemical changes as well as leaps in biological evolution. For example, phosphate rock formed during the Proterozoic. Oxygen appears to have increased significantly at the beginning - and at the end of the Proterozoic. The first event is known as the Great Oxidation Event, some 2.5 to 2 billion years ago. The second occurred around 1 billion years ago and brought oxygen levels up to modern amounts. This coincided with a spectacular amount of fossil diversity - known as the Cambrian Explosion. The phosphate deposits also occurred contemporary with evidence of continental rifting and extensive glaciation. However, the process of phosphate accumulation in the oceans is assumed to have taken millions of years - millions and millions of years of ocean outwash. That is a necessary prerequisite - it is the amount required rather than the time it took. Geological timescales dominate the paper - and the thesis (which is not necessarily obtuse). However, the germ of the idea inherent in the hypothesis appears to have an origin in modern run-off into the ocean observed, specifically at Chesapeake Bay - by high phosphorous fertiliser. It caused a massive algal bloom. This happened very quickly but the paper emphasizes the Proterozoic events took place over a long period of time - in inordinately very long period of time. The atmosphere was oxygenated progressively. Needless, to say, the rapidity of the modern algal bloom event will cause significant extinctions to occur rather than the appearance of new lineages.