Life at the poles provides insight into the earliest animals on Earth.
The amazing survival techniques of polar sea creatures may help explain how the first animals on Earth may have evolved earlier than older fossils suggest, according to a recent study. These primitive, primitive, and now extinct animals may have survived some of the harshest, coldest, and iciest times in the world. The results of the study were recently published in the journal Biology of global change.
The fossil record dates the earliest animal life on Earth to around 572-602 million years ago, just as Earth emerged from a massive ice age, although molecular studies suggest an earlier start, as far back as 850 million years ago. If true, this implies that the animals must have endured a period of multiple global ice ages when most of the world was covered in ice (Snowball and Snowball Earths), larger than any ever seen since. Had life emerged before or during these intense glacial periods, it would have encountered circumstances comparable to today’s marine ecosystems in Antarctica and the Arctic, and would have needed a similar set of survival strategies.
The expansion and contraction of ice sheets during cold and warm periods stimulated the development of thousands of distinct plant and animal species of Antarctica over millions of years. The same could be true of the evolution of animal life on Earth. While the polar regions seem to us the most hostile environments for life, they are the ideal place to study the history and possibility of life in the universe beyond our planet, such as on icy moons like Europa.
Marine biologist and lead author Dr. Huw Griffiths of the British Antarctic Survey (BAS), says: ‘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 about other planets.
He continues: “Whether it’s animals that live upside down on the underside of the ice instead of the seabed, sponges that live hundreds of kilometers under thick floating ice shelves, organisms adapted to living in marine waters colder than -2° C, or entire communities existing in the dark 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, icy conditions help drive the oceanic circulation, to transport oxygen into the ocean depths and to make these places more suitable for life».
Floating ice covers more than 19 million km2 of the seas around Antarctica and 15 million km2 of the Arctic Ocean during the winter. Under perhaps the most extreme Earth snowball, which lasted 50 to 60 million years during the Cryogenian period (720 to 635 million years ago), the entire world (510 million km²) is believed to have been buried in ice about a kilometer thick, but that’s no evidence that this ice was thin enough at the equator for seaweed 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,” says co-author Dr. Emily Mitchell , paleontologist and ecologist at the University of Cambridge. “But if animals had evolved before or during these global ice ages, they would have had to contend with extreme environmental pressures, but that may have helped force life to become more complex to survive.”
“Just as in Antarctica during the Last Glacial Maximum (33-14 thousand years ago), the massive amounts of advancing ice would have flattened the shallows, making them inhospitable to life, destroying fossil evidence, and forcing creatures to dive into the depths of the 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 paleontologist at BAS and co-author of the study, says: ‘Paleontologists often look to the past to tell us what future climate change might look like, but in this case, we were looking at the coldest and most extreme habitats on the planet for help us understand the conditions early animals might have faced and how modern polar creatures thrive under these extremes.”
Reference: “Animal Survival Strategies in Neoproterozoic Ice Worlds” by Huw J. Griffiths, Rowan J. Whittle, and Emily G. Mitchell, Oct. 11, 2022, Biology of global change.