How Animals May Have Conquered Snowball Earth

This article is from Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.

Planet Earth was once a cross between a freezer and a car wrecker. For most of the planet's history, everything from pole to pole has been buried under layers of ice a kilometer or more thick. Scientists call this snowball Earth.

Some ancient animals managed to survive this Ice Age some 720 to 580 million years ago, but they still have a long way to go. Despite their daring success, repeated expansions and contractions of massive ice sheets have left these powerful extremophile remains barely detectable in the fossil record, and scientists have little or no idea how they survived.

"It's like having a giant bulldozer," said Huw Griffiths of British Antarctica. "The next glacial expansion will just erase all of that and basically turn it to mush."

Despite the lack of direct evidence thanks to all this glacial upheaval, Griffiths argues that it's reasonable to assume that various species of animals bubbled up on Earth. This suggests that this flowering predates the so-called Cambrian Explosion, some 540 million years ago when an unprecedented variety of animal life appeared on Earth. "It's not a huge leap of the imagination that there were much smaller and simpler things before," said Griffiths.

A complete picture of animal life during this period is being lost, but Griffiths and colleagues are trying to understand what that looked like in the recent release.

The team looked at three different frozen periods. The first is Sturtian Snowball Earth, which formed about 720 million years ago. It lasts up to 60 million years. This is an incredible amount of time, almost the entire period between the end of the Dinosaur Age and the present. Next is Marinoan Snowball Earth, which began 650 million years ago and lasted only 15 million years. It was finally followed by the Gaskier Ice Age about 580 million years ago. This third ice age was even shorter and is often called Snowball Earth instead of Snowball Earth because the ice cover may not be as extensive.

Although ice destroyed most of the fossils from this period, scientists have found few remains. This rare fossil represents a strange animal that existed during the Gaskier Ice Age. Among these ancient inhabitants of Snowball Earth was a frondomorph, an organism somewhat resembling a fern leaf. Frondomorphs live attached to the seafloor beneath the ice, possibly absorbing nutrients from the water around them.

Without direct evidence, Griffiths and his colleagues argue that animal survival strategies during the great past freeze would likely have been replicated in life now inhabiting the most Earth-like environment on Earth: Antarctica.

Some modern Antarctic inhabitants, such as anemones, live stuck upside down at the bottom of the iceberg. One of the most popular krill feeding strategies is to graze microorganisms at this reverse level. Perhaps the first animals also foraged and found shelter in these places, Griffiths and his colleagues suspect.

It is also possible that the ups and downs of sea ice introduced algae or other ice-dwelling microorganisms into the seawater, allowing them to thrive, which could have provided food for other primitive animals.

One of the challenges for the inhabitants of the snowy plains is the possibility of a lack of oxygen, both because the oxygen content in the air is low and because the atmosphere is limited to mixing with water. But the oxygen-rich meltwater at the top of the water column could feed the animals that depend on it. Some Antarctic denizens that now live on the ocean floor, such as some species of feather stars, avoid this problem by relying on water currents to carry a constant stream of oxygen and nutrients from the small areas of water that are exposed from the surface to the depths. Ice. That rack. There's no reason to believe this didn't happen during the Slushball Earth Gaskiers era either.

"We're talking about a very simple life form... but at this point, you could use anything to become the king of beasts," said Griffiths.

Apart from frondomorphs, the seabed can also be inhabited by sponges. Some of the fossil evidence for sponges is older than Sturtian Snowball Earth, although there is some debate about this, Griffiths said.

Ashleigh Hood, a sedimentologist at the University of Melbourne in Australia who was not involved in the research, joked that "everyone, including us, has the oldest sponge they've found and no one else believes it."

Some modern sponges live in symbiosis with bacteria, which can help them find nutrients when other food is scarce. "This may be based on a survival strategy they had early in their history," suggests Hood.

Andrew Stewart, associate curator at New Zealand's Te Papa Tongarewa Museum, who also did not contribute to the article, has studied many species from Antarctica's harsh environment. Many of these organisms thrive in extremely dark, cold, or chemically toxic places. For Stewart, the extremists in Antarctica are a reminder of how powerful life on Earth really is, and perhaps always has been.

"It's just the most amazing place," he says. "Say no, damn it, nothing survives! Actually it does."

This article is from Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com .

Related story from Hakai Magazine: