WASHINGTON, April 4 (Reuters) – Life on our planet faced a severe test during the Cryogenian period, which lasted from 720 million to 635 million years ago when Earth was frozen twice by glaciers and looked like a shimmering white snowball from space.
Life somehow managed to survive on what’s known as “Snowball Earth,” and a new study offers a deeper understanding of why.
Fossils identified as seaweed from black shale in central China’s Hubei province indicate that habitable marine environments were more widespread than previously known, scientists said Tuesday. The findings support the idea that it was a “slushball Earth” where early forms of complex life – basic multicellular organisms – survived even in mid-latitudes previously thought to be frozen solid.
The fossils are from the second of two periods during the Cryogenian period when massive ice sheets extended from the poles toward the equator. This interval, called the Marinoan Ice Age, lasted from about 651 million to 635 million years ago.
“The main finding of this study is that open-water – ice-free – existed in the mid-latitude oceanic region during the waning phase of the Marinoan Ice Age,” said the study’s lead author Huai Song, a geobiologist at the China University of Geosciences. Published in Journal Nature communication.
“Our study shows that, at least near the end of the Marinoan ‘Snowball Earth’ event, habitable areas extended into the mid-latitude oceans, much further than previously thought. Previous research had argued that such habitable areas were, at best, only tropical. existed in regions. oceans. More extensive areas of habitable oceans better explain where and how complex organisms such as multicellular seaweeds lived,” added Song.
The findings show that the world’s oceans were not completely frozen and habitable shelters existed where multicellular eukaryotic organisms — domains of life including plants, animals, fungi, and mostly single-celled organisms called protists — could survive, Song said.
Earth was formed about 4.5 billion years ago. The first single-celled organisms arose within about the first billion years of the planet’s existence. Multicellular organisms arrived later, perhaps 2 billion years ago. But it was only after the Cryogenian that warmer conditions returned, paving the way for the rapid expansion of various life forms around 540 million years ago.
Scientists are trying to better understand the origin of “Snowball Earth”. They believe that the sun’s warming reaches the planet’s surface as solar radiation bounces away from the white ice sheets.
“It is widely believed that atmospheric carbon dioxide levels dropped just prior to these events, causing the polar ice caps to expand and therefore reflect more solar radiation into space and the polar ice caps to expand further. And the Earth snowball spiraled into Earth conditions. ,” said Shuhai Xiao, a geologist at Virginia Tech and co-author of the study.
Fossils of seaweed and some other multicellular organisms were identified in the black shale. This seaweed – a primitive plant – was a photosynthetic organism living on the sea floor in a shallow marine environment illuminated by sunlight.
“The fossils were preserved as compressed sheets of organic carbon,” said Qin Ye, a China University of Geosciences paleontologist and co-author of the study.
Multicellular organisms, including red algae, green algae and fungi, appeared before the Cryogenian and survived the “Snowball Earth”.
The Cryogenian ice age was much worse than the one that humans lived in, ending about 10,000 years ago.
“Compared to the most recent ice age, the glacier coverage was much more extensive and, more importantly, much of the ocean was frozen,” Xiao said.
“It’s fair to say that ‘Snowball Earth’ events were important challenges for life on Earth,” Xiao added. “It is conceivable that these ‘snowball Earth’ events could have caused major extinctions, but life, including apparently complex eukaryotic organisms, was able to survive, demonstrating the resilience of ecosystems.”
Reporting by Will Dunham, Editing by Rosalba O’Brien
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