First animals on Earth may have evolved earlier than fossils suggest

According to new research, the first animals on Earth could have evolved much earlier than the oldest fossils suggest. This new discovery can be explained by the amazing survival strategy of polar marine creatures, scientists have said.

The first, and now extinct, animals are predicted to have lived through some of the most extreme cold and icy periods the world has ever seen.

The research was published in this week’s edition of Global Change Biology.

Molecular studies versus fossil records

Fossil records place the first animals on Earth around 572–602 million years ago, just as the world came out of a huge ice age. In contrast, molecular studies suggest an earlier origin, up to 850 million years ago.

If molecular studies are correct, animals must have survived during a time influenced by multiple global ice ages, when the majority of the planet was covered by ice. Animal life during these times would have required similar survival strategies to those in modern Antarctic marine habitats.

The evolution of Antarctica’s unique animals and plant species has been driven by the expansion and contraction of ice sheets during different weather conditions. The research suggests that this could also be the case for the first animals on Earth.

Dr Huw Griffiths of the British Antarctic Survey, said: “This work highlights how some animals in the polar regions are incredibly adapted to life in and around the ice, and how much they can teach us about the evolution and survival of life in the past, or even on other planets.

“Whether it is animals living upside down on the underside of ice instead of the seafloor, sponges living hundreds of kilometres under thick floating ice shelves, organisms that are adapted to live in seawater colder than minus two degrees, or whole communities existing in the darkness on food sources that don’t require sunlight, Antarctic and Arctic life thrives in conditions that would kill humans and most other animals. But these cold and icy conditions help to drive ocean circulation, carry oxygen into the ocean depths and make these places more suitable for life.”

Could climate change have destroyed evidence of the first animals?

During the Cryogenian period, around 720 to 635 million years ago, the whole world is believed to have been covered in ice around one kilometre thick. The research suggests that this ice was thin enough at the equator, allowing the first animals to survive.

“The fact that there is this huge difference in the timing of the dawn of animal life between the known fossil record and molecular clocks, means that there are huge uncertainties about how and where animals evolved,” explained Dr Emily Mitchell, Palaeontologist and Ecologist at the University of Cambridge.

She continued: “If animals did evolve before or during these global ice ages, they would have to contend with extreme environmental pressures, but ones that may have helped to force life to become more complex to survive.

“Just like in Antarctica during the Last Glacial Maximum, the huge amounts of advancing ice would have bulldozed the shallows, making them inhospitable to life, destroying evidence of the first animals and forcing creatures into the deep sea. This makes the chances of finding fossils from these times less likely and sheltered areas and the deep sea the safest places for life to evolve.”

Dr Rowan Whittle, Polar Palaeontologist at the British Antarctic Survey, concluded: “Palaeontologists often look to the past to tell us how future climate change might look. However, in this case, we were looking to the coldest and most extreme habitats on the planet to help us understand the conditions that the first animals might have faced, and how modern polar creatures thrive under these extremes.”

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