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Ocean oxygen is key to animal evolution

Edinburgh scientists have helped show how complex life forms began to evolve billions of years after Earth was formed.

Scientists have long been puzzled about why complex life forms began to appear some 550 million years ago – three billion years after life on the planet comprised nothing more complex than algae.

A team of scientists, including Edinburgh researchers, has put forward some of the strongest evidence yet to support the idea that rising levels of oxygen in the oceans were responsible for the emergence of skeletal animals. 

Fuel to evolve

The study supports the idea that a rise in the level of oxygen in the oceans gave simple life forms the fuel they needed to evolve skeletons, the ability to move around, and other typical features of modern animals.

Details of rock samples gathered by Edinburgh scientists on fieldwork in Namibia were analysed by a team from University College London and the Universities of Edinburgh, Leeds and Cambridge as well as the Geological Survey of Namibia.

The study analysed the chemical composition of the well preserved rocks from the Nama Group – sediments which were once in the ocean where there are fossils of early Cloudina, Namacalathus and Namapoikia animals.

High oxygen

The new study is the first to distinguish between bodies of water with low and high levels of oxygen.

It shows that poorly oxygenated waters did not support the complex life that evolved immediately prior to this period.

This suggests that the presence of oxygen was the key factor in the appearance of these animals.

The research is published in the journal Nature Communications.

Ocean regions

By comparing waters with high and low levels of oxygen, and showing that early skeletal animals were restricted to well oxygenated waters, the team provides strong evidence that oxygen was a key requirement for the animals’ development.

However, such oxygen-rich environments may have been in short supply, limiting space in the ocean for the earliest animals.

By combining geochemistry with the distribution of ancient fossils buried in rocks we have uncovered the strongest clues to date as to how animals began to evolve millions of years ago – and how the availability of oxygen in the oceans was most likely the determining factor in their appearance.

Professor Rachel WoodSchool of GeoSciences