How Animals May Have Conquered Snowball Earth

Original copy of the article.

Planet Earth was once a cross between a freezer and a car shredder. For most of the planet's history, everything from pole to pole was submerged under a kilometer-thick layer of ice. Scientists call this snowball Earth.

Some primitive animals managed to survive this cold period from about 720 to 580 million years ago, but they had a lot of work to do. Despite their heroic achievements, the repeated expansion and contraction of the great ice sheets crushed the remains of the hardy extremists, leaving almost no trace of them in the fossil record, and scientists have little idea how they managed to survive.

"It basically looks like a giant bulldozer," said Hugh Griffiths of British Antarctica. "The next glacier expansion will take everything away and turn it into pulp."

Despite the lack of direct evidence for all these glacial movements, Griffiths argues that it is reasonable to assume that various animals settled the Earth in a snowball. This suggests that this flowering may have occurred in what is known as the Cambrian explosion, about 540 million years ago when a great diversity of fauna appeared on Earth. "It's not a huge leap of the imagination that there have been a lot of small, simple things before," says Griffiths.

The full picture of the fauna is lost at this point, but Griffiths and his colleagues are trying to understand what it might have looked like in their latest work.

The team tested three different freezing periods. The first was Earth's sturgeon snowball, which began about 720 million years ago. It lasted up to 60 million years. This is an incredibly long time, almost as long as the period from the end of the age of dinosaurs to the present day. Then there was the sea ice that covered the Earth, which began 650 million years ago and lasted only 15 million years. The Gasquier Ice Age followed about 580 million years ago. This third ice age was short and is often referred to as the ice sheet rather than the snow land, as the ice sheet was probably not that extensive.

Although the ice has tainted most of the fossils from this period, scientists have found some remains. These rare fossils represent the strange creatures that existed during the Gaskian Ice Age. Among these ancient inhabitants of the earth were frondomorphs, organisms that somewhat resemble fern leaves. Frondemorphs lived on the ocean floor beneath the ice and could absorb nutrients from the water flowing around them.

Instead, in the absence of direct evidence, Griffiths and his colleagues argue that survival strategies used by animals during past great glaciations may be replicated by life living in the most similar environment on Earth today, Antarctica.

Many animals, such as starfish and sponges, live on the sea floor under the Antarctic ice. Photo by Norbert W/Minden Pictures

Some modern inhabitants of Antarctica, such as anemones, live upside down on the surface under the sea ice. One of the preferred feeding strategies of krill is to feed on microorganisms in this inverted layer. Griffiths and his colleagues suspect that early animals also sought food and shelter in such places.

It is also possible that as the sea ice expands and weakens, algae or other ice-dwelling microorganisms may enter the seawater, allowing them to thrive, which may become food for other primitive organisms.

One of the problems faced by the inhabitants of Snowball Earth was the possible lack of oxygen, both due to the low level of oxygen in the air and the limited mixing of the atmosphere with water. But oxygen-rich meltwater in the water column can support organisms that depend on it. Some animals that now live on the Antarctic seabed, such as some species of feather stars, solve this problem by relying on water currents to provide a constant flow of oxygen and nutrients from small areas of open water on the surface in the depth of the ice. . . shelf There is no reason to believe that this did not also happen during Gasquier's Slushball Earth.

"We're actually talking about very simple life forms... but then, that's all it takes to be king of the beasts," says Griffiths.

Along with phrondomorphs, sponges can also live at the bottom of the sea. Some fossil evidence of sponges dates back to long before sedges appeared on Earth, though that's debatable, Griffiths said.

Ashley Hood, a sediment expert at the University of Melbourne in Australia who was not involved in the research, joked that "everyone, including us, has the oldest sponge they can find and nobody buys it." .

Some modern sponges are symbiotic with bacteria, which can help them access nutrients when other food supplies are in short supply. "It's probably based on a survival strategy that was early in their history," Hood suggests.

Andrew Stewart, associate curator at the Museum of New Zealand Te Papa Tongarewa, who was not involved in the publication, has studied countless species in the harsh conditions of Antarctica. Many of these organisms thrive in places that are extremely dark, cold, or chemically toxic. For Stewart, the Antarctic extremists are a reminder of how reliable life on Earth is and likely always will be.

"It's the most amazing place," he says. "Go hell no nothing will survive! Actually it might."