Just over 500m years ago life on Earth got souped-up, going from simple single-celled organisms to sophisticated multicellular lifeforms. The Cambrian explosion produced an array of weird and wonderful new inhabitants, such as the five-eyed opabinia and the spiky slug wiwaxia. Pulses of oxygen in the atmosphere and ocean are thought to have fuelled the diversification, but until now it has not been clear what drove the oxygen fluctuations. Now a study suggests changes in the Earth’s orbit may have been behind these evolutionary pulses.
Researchers used a climate and biogeochemical model and looked at how periodic shifts in Earth’s orbit affected the amount of solar energy reaching Earth. They discovered that the changes in solar energy every two to three million years kept in step with the ups and downs in observed oxygen levels.
Writing in Geophysical Research Letters, the researchers suggest that the changes in solar energy caused climatic changes that altered the amount of weathering of land surfaces – especially at high latitudes – with periods of fast weathering releasing bursts of nutrients into the oceans, which drove photosynthesis and pushed up oxygen levels, fuelling the high speed evolutionary changes.
Similar orbital changes have occurred at other times, but only the Cambrian period had all the ingredients in place to enable this exceptional evolutionary burst.