The team considered three different frozen periods. The first was the Sturtian snowball Earth, which began about 720 million years ago. It lasted for up to 60 million years. This is a mind-blowingly long time\u2014it\u2019s nearly as long as the period between the end of the dinosaur era and today. Then came the Marinoan snowball Earth, which started 650 million years ago and lasted a mere 15 million years. It was eventually followed by the Gaskiers glaciation around 580 million years ago. This third glaciation was shorter still and is often called a slushball rather than a snowball Earth because the ice coverage was likely not as extensive.<\/p>\n
Though the ice smushed most of the fossils from these periods, scientists have found a handful of remnants. These rare fossils portray the weird animals that existed around the time of the Gaskiers glaciation. Among these ancient slushball-Earth dwellers were the frondomorphs\u2014organisms that looked a bit like fern leaves. Frondomorphs lived fixed to the seafloor beneath the ice and possibly absorbed nutrients from the water as it flowed around them.<\/p>\n
Short on direct evidence, Griffiths and his colleagues instead argue that the survival strategies of animals during the great freezes of the past are likely echoed by the life that dwells in the most similar environment on Earth today\u2014Antarctica.<\/p>\n
![\"\"](\"https:\/\/hakaimagazine.com\/wp-content\/uploads\/body-snowball-extremophiles.jpg\")
<\/a>Many animals, such as sea stars and sponges, eke out an existence on the seafloor beneath the ice off Antarctica. Photo by Norbert Wu\/Minden Pictures<\/p><\/div>\n
Some modern Antarctic inhabitants such as anemones<\/a> live upside down affixed to the underside of the sea ice. One of the favorite feeding strategies of krill is grazing microorganisms on this upturned plane. Perhaps early animals foraged and found shelter in such locations, too, Griffiths and his colleagues suggest.<\/p>\n It\u2019s also possible that the waxing and waning of sea ice introduced algae or other microorganisms living on the ice into seawater allowing them to bloom, which might have provided food for other early animals.<\/p>\n One of the challenges that inhabitants of a snowball Earth faced was the possible lack of oxygen, both because the oxygen levels in the air were low and because there was limited mixing from the atmosphere into the water. But oxygenated meltwater high in the water column might have supported animals that depended on it. Some denizens that live on the Antarctic seafloor today, such as certain species of feather star<\/a>, solve this problem by relying on water currents to bring a steady flow of oxygen and nutrients from the small areas of open water at the surface to deep below the ice shelves. There\u2019s no reason to think this didn\u2019t happen during the Gaskiers slushball Earth period, too.<\/p>\n \u201cWe are really talking about very basic forms of life \u2026 but at the time that\u2019s all you\u2019d have needed to be king of the animals,\u201d says Griffiths.<\/p>\n Alongside frondomorphs, the seafloor might also have been inhabited by sponges. Some fossil evidence of sponges dates back to well before the Sturtian snowball Earth, though there is some debate over this, says Griffiths.<\/p>\n Ashleigh Hood, a sedimentologist at the University of Melbourne in Australia who was not involved in the research, jokes that \u201ceveryone, including us, has their oldest sponge that they\u2019ve found in the record and no one else believes them.\u201d<\/p>\n