Information about the first animals on Earth from life at the poles

According to a new study, the surprising survival strategies of polar sea creatures may help explain how the first animals on Earth may have appeared earlier than the oldest fossils suggest. These first simple and now extinct animals may have lived through some of the most extreme, cold and icy periods the world has ever seen. The study is published in the journal Global change in biology October 12, 2022

The fossils the earliest places animal life on Earth 572–602 million years ago, when the world emerged from the Great Ice Age, while molecular studies suggest an earlier origin, up to 850 million years ago. If correct, this means that animals would have had to survive a time affected by multiple global ice ages, when all or large parts of the planet were encased in ice (snowball and slush Earth) far greater than any since. If animal life did arise before or during these extreme ice ages, it would have encountered conditions similar to modern marine habitats in Antarctica and the Arctic today, and would have required similar survival strategies.

Over millions of years, the expansion and contraction of the ice sheet during cold and warm periods has led to the evolution of thousands of unique Antarctic animal and plant species. The same may apply to the evolution of animal life on Earth. While the polar regions appear to humans to be the most hostile environment for life, they are an ideal place to study the past and the potential for life in the universe beyond our planet, such as on icy moons like Europa.

Marine biologist and lead author Dr Hugh Griffiths of the British Antarctic Survey (BAS) says: “This work shows how some animals in polar regions incredibly adapted to life in and around ice, and what they can teach us about the evolution and survival of life in the past or even on other planets. Be it animals that live upside down on the lower surface of the ice rather than on the seabed, sponges that live hundreds of kilometers under a thick floating ice shelf, organisms adapted to live in seawater colder than -2°C, or whole communities that exist in the dark. on food sources that do not require sunlight, Antarctic and Arctic life thrives in conditions that would kill humans and most other animals. But these cold and icy conditions help stimulate ocean circulation, transport oxygen to the ocean depths and make these places more habitable.”

Floating ice occupies more than 19 million km² seas around Antarctica and 15 million km² Arctic Ocean in winter. Under what is perhaps Earth’s most extreme snowpack, which lasted from 50 to 60 million years during the Cryogenic Period (720-635 million years ago), it is believed that the entire world (510 million km²) was buried in ice about a kilometer thick, but there there is some evidence that this ice was thin enough at the equator to allow seaweed to survive.

“The fact that there is such a huge difference in the timing of animal life between the known fossil and molecular clocks means that there is enormous uncertainty about how and where animals evolved,” says co-author Dr Emily Mitchell, a paleontologist and ecologist at Cambridge University. “But if animals did evolve before or during these global ice ages, they would have had to deal with extreme environmental pressures, but one that may have helped make life more complex to survive.

“Just like in Antarctica during the last glacial maximum (33,000-14,000 years ago), huge amounts of advancing ice bulldozed the shallows, making them uninhabitable, destroying fossil evidence and the displacement of creatures into the deep sea. This makes the chances of finding fossils from those times less likely, and protected areas and deep seas become the safest places for life to develop.”

Dr Rowan Whittle, polar palaeontologist at BAS and co-author of the study, said: ‘Palaeontologists often look to the past to tell us what climate change might look like in the future, but in this case we looked at the coldest and most extreme habitats. on the planet to help us understand the conditions that the first animals might have encountered, and how modern polar creatures thrive in these extremes.”