17:13 26 July 2016
A recent study has found that oxygen levels that were needed to sustain our multicellular ancestors did not spread equally around the world.
The end of the Proterozoic period has seen photosynthetic bacteria producing oxygen, a process that is believed to have started as long as 3.2 billion years ago. However, it was not until between 1.8 billion and 600 million years ago that the first animals are thought to have emerged. Scientists said that this was due to the way in which oxygen was absorbed and dissolved in the ocean.
Researchers said that the oxygen in our planet initially built up in the warm shallow oceans around the tropics, which would have given animal life a spluttering start. However, just before the animals started to get going, oxygen levels in the ocean shifted towards the poles, giving cold water species a chance to emerge and flourish. The researchers also noted shifting oxygen hotspots that have made it more challenging for animals to evolve.
Dr Chris Reinhard, a geochemist at the Georgia Institute of Technology, and his team said: “We suggest that early multicellular organisms would have had to contend with a "patchy" and evolutionarily restrictive oxygen landscape for much of the Proterozoic time, despite background local oxygen levels that may, in some cases, have been sufficient to fuel their metabolic needs.