Tuesday, September 18, 2007

Oxygen: Evolution's powerbooster

An April article on oxygen from New Scientist has been niggling me for months. The story given is a neat account of the development of life on earth being directly connected to the concentration of oxygen in the atmosphere.

Written by Peter Ward, extracted from his book Out of Thin Air (Joseph Henry Press), it attributes the emergence and subsequent re-emergence of animals directly to the rise of atmospheric oxygen to today’s levels and above. Modelling of oxygen levels is extracted from a system called Geocarbsulf (Yale University) – see here.

This picture presents somewhat of a refinement of traditional views of oxygen levels over time, as depicted in the Wikipedia article on oxygen amongst others. The narrative and evidence is convincing – if that modelling wasn't specifically tied to the known dates for animals inhabiting the terrestrial environment (ie a causality issue) - but the context of story, publication and author are persuasive.

The narrative further attributes the rise of large land animals - dinosaurs in particular – specifically to increased oxygen and more complex respiration mechanisms. More sophisticated than mammals, in fact. Birds and, he demonstrates, dinosaurs have air sacs that permit continuous respiration as opposed to the old in-out. Ward’s keynote example is geese migrating over the Himalayas at altitudes that would kill humans. He depicts the air sacs as located specifically in birds’ hollow bones, a mechanism subsequently identified in their ancestors the dinosaurs.

The article - and book - go into much more detail on the circumstances that lead to these changes in oxygen levels, and the outcomes. There may be some useful lessons from this for today's situation, although it's always hard to integrate the narratives of such different scales of time: the ponderous geological changes versus the the anthropogenic changes being wrought at a breakneck human pace.

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