Cambrian Explosion: role of oxygen (Introduction)

by dhw, Wednesday, February 19, 2014, 15:33 (2237 days ago) @ David Turell

DAVID: Because oxygen content rose to near present levels in pre-Cambrian times it is proposed to be one of the major triggers of the explosion. Not so fast says this new paper. Many animals can survive on very low oxygen:
"However new studies of a common sea sponge from Kerteminde Fjord in Denmark shows that this explanation needs to be reconsidered. The sponge studies show that animals can live and grow even with very limited oxygen supplies.

"In fact animals can live and grow when the atmosphere contains only 0.5 per cent of the oxygen levels in today's atmosphere.

"Our studies suggest that the origin of animals was not prevented by low oxygen levels", says Daniel Mills, PhD at the Nordic Center for Earth Evolution at the University of Southern Denmark."

Read more at: http://phys.org/news/2014-02-theory-animals-earliest-animal-life.html#jCp

I have read more. Quote: "The living animals that most closely resemble the first animals on Earth are sea sponges. The species Halichondria panicea lives only a few meters from the University of Southern Denmark's Marine Biological Research Centre in Kerteminde, and it was here that Daniel Mills fished out individuals for his research.
When we placed the sponges in our lab, they continued to breathe and grow even when the oxygen levels reached 0.5 per cent of present day atmospheric levels", says Daniel Mills."

Many apologies if I am being dense here, but surely the test is not whether the earliest animals could live with 0.5%, but whether LATER animals can. If they can't, then clearly later animals could only evolve when the level of oxygen increased. Perhaps, David, you could explain how tests on earlier animals prove that later animals could have existed on the same amount of oxygen but didn't.

QUOTE: "His colleagues from the Nordic Center for Earth Evolution have previously shown that oxygen levels have actually risen dramatically at least one time before complex life evolved. Although plenty of oxygen thus became available it did not lead to the development of complex life."

We would need to know more details. How dramatically? Dramatically enough to support modern animals? How accurate can any of these measurements be? But in any case, the fact that conditions are suitable for innovations does not mean that innovations will take place. (The same applies to life itself.) That depends on the nature of the organisms that are around, and how they interact with those conditions.


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