(ORDO NEWS) — According to one hypothesis, about 750 million years ago, the entire Earth was covered by one giant glacier.
Such a state was called very peculiarly: earth-snowball. And our frozen planet was ruled by strange creatures.
Five hundred million years before the dinosaur era, our frozen planet was ruled by strange creatures.
Planet Earth was once a cross between a freezer and a hydraulic press. For long historical epochs, the oceans from pole to pole were covered with an ice sheet about a kilometer thick.
Scientists call it “Snowball Earth” or “Snowball Earth”.
Some of the early organisms managed to survive the cold era from about 720-580 million years ago, although the task was not an easy one.
However, despite their remarkable will to live, the constant expansion and contraction of giant ice sheets turned the remains of hardy extremophiles into dust, leaving almost no trace in the fossil record, and scientists have difficulty understanding how they managed to survive.
“In general, it looks like a giant bulldozer,” says Hugh Griffiths of the British Antarctic Survey. “Each subsequent glaciation just erased everything under zero, turning everything into mush.”
Although we don’t have direct evidence – thanks to a giant glacial crusher – Griffiths thinks it’s logical to assume that Snowball Earth was inhabited by a very diverse life.
He suggests that this heyday anticipated the so-called Cambrian Explosion, which occurred about 540 million years ago, when an unprecedented variety of animal life appeared on Earth. “It doesn’t take a brain to suggest that it was preceded by smaller and simpler organisms,” says Griffiths.
The full picture of animal life at that time has been lost, but in a recent paper, Griffiths and colleagues tried to figure out what it might have been like.
His team looked at three different periods of glaciation. The first one, the Stertskoe, began about 720 million years ago and lasted up to 60 million years.
This is mind-bogglingly long almost as much time has elapsed between the end of the dinosaur era and today. It was followed by the Marinoan glaciation – it began 650 million years ago and lasted “only” 15 million years.
The third and last was the Gasquier glaciation about 580 million years ago. It turned out to be even shorter, and some even call it “slushy”, meaning that the Earth’s ice cover was no longer so extensive.
Although the ice crushed most of the fossils from these periods, scientists did find some remains. These rare finds tell us how strange animals lived during the “slushy” glaciation of Gasquier.
Among them were frontomorphs – these organisms vaguely resembled fern leaves. Frondomorphs were attached to the seafloor under the ice and may have absorbed nutrients from the water.
Without direct evidence, Griffiths and colleagues still argue that the survival strategies of animals during the great frosts of the past certainly echoed the current inhabitants of the most similar environment on Earth – Antarctica.
Some inhabitants of the Antarctic, such as anemones, live upside down and attach themselves to the lower edge of the sea ice. Krill loves to feed on them, eating them from an inverted plane. Griffiths and colleagues suggest that the first animals could forage and find shelter in similar places.
In addition, due to the alternating melting and growth of sea ice, algae or other microorganisms got from the ice surface into the sea water and bloomed, becoming, in turn, food for other early animals.
Among other things, the inhabitants of Snowball Earth could suffer from a lack of oxygen – both due to its low content in the air, and due to the fact that the atmosphere hardly mixed with water. But oxygenated meltwater in the upper layers of the ocean could support the animals.
The inhabitants of the seabed of modern Antarctica – for example, some types of feather stars – solve this problem thanks to water flows: they provide a constant supply of oxygen and nutrients from small “windows” of open water on the surface into the depths of the ice shelf.
Nothing foreshadows that during the glaciation, Gasquier was fundamentally different.
“Actually, we are now talking about extremely primitive life forms… But at that time, more was not required to become the king of beasts,” says Griffiths.
Along with frontomorphs, sponges could also live on the seabed. According to Griffiths, some fossil forms of sponges date back well before the Sturt glaciation, although this is a matter of debate.
University of Melbourne sedimentologist Ashley Hood, who was not involved in the study, jokes: “It turns out that everyone has their own oldest sponge, and so do we. Therefore, no one trusts anyone.”
Some modern sponges live in symbiosis with bacteria, thanks to which they receive nutrients when other food is not enough. “This survival mechanism could have been around since the dawn of history,” says Hood.
Andrew Stewart, assistant curator at the Te-Papa-Tongarewa National Museum of New Zealand, also not involved in the study, studied countless species that had survived the harsh Antarctic environment. Many of them survive even in dark, icy or chemically poisonous places.
For Stewart, the Antarctic extremophiles are a living reminder of how resilient the inhabitants of the Earth are. And so it has always been.
“It’s just an amazing place,” he says.
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