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Revolutions that made the Earth$
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Tim Lenton and Andrew Watson

Print publication date: 2011

Print ISBN-13: 9780199587049

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199587049.001.0001

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Animals and oxygen

Animals and oxygen

(p.294) (p.295) 15 Animals and oxygen
Revolutions that made the Earth

Tim Lenton

Andrew Watson

Oxford University Press

This chapter begins by addressing the possibility that the appearance of intelligent life was held back by a simple global environmental constraint: lack of oxygen in the atmosphere. Looking at the rapid evolution of life in the Cambrian, one might wonder if there is any reason why intelligent life could not have emerged in Cambrian times. The Phanerozoic began with an evolutionary bang: the rate of appearance of new species in the Cambrian explosion, and in the preceding Ediacaran period, is well above the levels seen in the preceding three billion years of life on Earth. Origination rates were also far greater than at any time since. Together with a plethora of hard-shelled marine invertebrates, the first marine vertebrates evolved early in the Cambrian. These early ‘chordates’ were the start of the branch of the tree of life that would eventually lead to us.

Keywords:   intelligent life, global environmental constraint, lack of oxygen, Cambrian, Phanerozoic

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