Low levels of atmospheric oxygen might not have delayed animal evolution

Challenging a long held view that low levels of atmospheric oxygen prevented the evolution of animals, new findings show that primitive animals can survive under extremely low oxygen conditions, according to researchers at the University of British Columbia, the University of Southern Denmark, and the California Institute of Technology.

The findings, published Monday in the Proceedings of the National Academy of Sciences, show experimental evidence that sponges, basal animals similar to the earliest fossil animals, can survive, breathe and feed with atmospheric oxygen levels as low as 0.5 to 4 per cent of current levels.

These lower oxygen levels were likely present on Earth millions of years before the appearance of animals in the fossil record.

"Our work supports the need for multiple environmental, ecological and developmental processes to be considered before we can hope to explain the origination of complex life on Earth—as opposed to relying only on the appearance of oxygen in the atmosphere," says CarriAyne Jones, a post doctoral fellow with the departments of Microbiology and Immunology and Earth, Ocean and Atmospheric Sciences at UBC who assisted with the research while at the University of Southern Denmark.

An increase in the oxygen content of the Earth’s atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. Current thinking holds that low levels of atmospheric oxygen delayed the origin of animals up until 542 million years ago.

Oxygen requirements of the earliest animals www.pnas.org/cgi/doi/10.1073/pnas.1400547111