This article originally appeared on Hakai Magazine, an online publication on science and society in coastal ecosystems. Read more articles like this at hakaimagazine.com.
Planet Earth used to be something like a cross between a deep freeze and a car wreck. For much of the planet’s history, everything from pole to pole was sandwiched under a blanket of ice a kilometer or more thick. Scientists call this snowball the Earth.
Some early animals managed to endure this icy era from about 720 to 580 million years ago, but they had their work cut out for them. Despite their valiant successes, the repeated expansion and contraction of giant ice sheets pulverized the hardy extremophiles’ remains, leaving almost no trace of them in the fossil record, and scientists had little or no idea how they managed to survive.
“It’s basically like having a giant bulldozer,” says Huw Griffiths of the British Antarctic Survey. “The next ice expansion would have just erased all that and turned it to mush, basically.”
Despite the lack of direct evidence thanks to all the glacial churning, Griffiths argues that it is reasonable to suggest that a wide range of animal life inhabited the snowball land. He suggests that this flourishing would have preceded the so-called Cambrian explosion, a period about 540 million years ago when a great and unprecedented diversity of animal life appeared on Earth. “It’s not a huge leap of the imagination that there were much smaller, simpler things that existed before that,” Griffiths says.
The whole picture of animal life during this time is lost, but Griffiths and his colleagues take a stab at a new paper to try to figure out what it is Power has looked.
The team considered three different frozen periods. The first was the Sturtian snowball Earth, which began about 720 million years ago. It lasted up to 60 million years. This is an incredibly long time – it is almost 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 only 15 million years. It was eventually followed by the Gaskier glaciation around 580 million years ago. This third glaciation was even shorter and is often referred to as a slushball rather than a snowball because the ice coverage was likely not as extensive.
Although the ice crushed most fossils from these periods, scientists have found a handful of remains. These rare fossils depict the strange animals that existed around the time of the Gaskier glaciation. Among these ancient slushball earthlings were frondomorphs – organisms that looked a bit like fern leaves. Frondomorphs lived attached to the seafloor under the ice, possibly absorbing nutrients from the water as it flowed around them.
Short of direct evidence, Griffiths and his colleagues argue instead that animal survival strategies during past great freezes are likely mirrored by life living in the most similar environment on Earth today—Antarctica.
Some modern Antarctic inhabitants such as anemones live upside down attached to the underside of the sea ice. One of the krill’s favorite feeding strategies is to graze on microorganisms on this upturned plane. Perhaps early animals foraged and found shelter in such places as well, Griffiths and his colleagues suggest.
It is also possible that the waxing and waning of the sea ice introduced algae or other micro-organisms that live on the ice into the sea water so that they could bloom, which may have provided food for other early animals.
One of the challenges facing inhabitants of a snowball Earth was the possible lack of oxygen, both because oxygen levels in the air were low and because there was limited interference from the atmosphere into the water. But oxygenated meltwater high up in the water column may have supported animals that depended on it. Some inhabitants of the Antarctic seafloor today, such as certain species of feather stars, solve this problem by relying on water currents to obtain a steady flow of oxygen and nutrients from the small areas of open water at the surface to deep beneath the ice shelves. There’s no reason to think this didn’t happen during Gaskier’s slushball Earth period as well.
“We’re really talking about very basic life forms … but at that point, that’s all you needed to be the king of the beasts,” says Griffiths.
Alongside frondomorphs, the sea floor may also have been inhabited by sponges. Some fossil evidence of fungi dates back to well before the Sturtian Snowball Earth, although there is some debate about this, Griffiths says.
Ashleigh Hood, a sedimentologist at the University of Melbourne in Australia who was not involved in the research, jokes that “everyone, including us, has their oldest sponge that they’ve found in the record and nobody else believes them.”
Some modern fungi live symbiotically with bacteria, which can help them gain access to nutrients when other food is scarce. “It’s probably based on a survival strategy they had very early in their history,” Hood suggests.
Andrew Stewart, assistant curator at the Museum of New Zealand Te Papa Tongarewa who was also not involved in the paper, has studied countless species from harsh Antarctic environments. Many of these organisms can survive in incredibly dark, cold or chemically toxic places. For Stewart, Antarctic extremophiles are a reminder of how robust life on Earth really is—and perhaps always has been.
“It’s just the most amazing place,” he says. “You go, no, old ladies, nothing can survive there! Well, actually it can.”