Cambrian Explosion: role of oxygen (Introduction)

by dhw, Thursday, January 07, 2016, 12:23 (1542 days ago) @ David Turell

QUOTE: “Maybe the oxygen rise had less to do with the animal revolution than we previously assumed," says Hammarlund."
David's comment: This leaves the Cambrian period with no explanation from an evolutionary standpoint as to why it appeared when it did. It remains the main stumbling block to Darwin's chance theory.

dhw: If the Cambrian produced NEW phyla, how can anyone possibly know that those hitherto non-existent organisms could have existed on 4% of the oxygen we have today? Look at the bold: should be, probably, it is likely, maybe...This is pure speculation, and I am surprised you take it seriously. The Cambrian remains an unsolved mystery, the oxygen factor remains a possible explanation, though we still need a mechanism to take advantage of whatever changes took place.

DAVID: I agree with you the Cambrian is a major mystery, but their point that sponges and simple worms can live on 4% O2 raises the issue of how much oxygen is really enough for the complex Cambrians. Today humans are adapted to live at very high altitudes. For example at Mexico city (7,500 feet) available oxygen is 50%. That is the equivalent to 10% of the 20% at sea level. In Cuzco at 11,000 feet O2 is equivalent to roughly 75% less, about 5% available. Remember the atmosphere has the same percentage composition since these are 'equivalent' assumptions to what might have been pre-Cambrian. The authors' points are not unreasonable.

Their argument is pure speculation. The fact that pre-Cambrian organisms and some existing organisms could live on 4%, and some existing organisms can adapt to lower levels, does not mean that NEW organisms could have come into existence at that level. The authors' vague speculations, acknowledged in their tentative “maybe”, do not in any way invalidate the possibility that the Cambrian Explosion was triggered by an increase in oxygen offering opportunities for new forms of life. But it remains a hypothesis, and still doesn't solve the mystery of the mechanism that enables innovation.

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