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 the Earth froze twice due to runaway glaciations and from space looked like a shimmering white snowball.
Life has somehow managed to survive during this time called “Snowball Earth,” and a new study offers a deeper understanding of why.
Scientists said on Tuesday that fossils identified as seaweed discovered in black shale in central China’s Hubei Province indicate that habitable marine environments were more widespread at the time than previously known. The findings support the idea that it was more of a “solid globe” as it endured the first forms of complex life – basic multicellular organisms – even in mid-latitudes previously thought to be frozen solid.
The fossils date back to the second of the two times during the cooling period when massive ice sheets extended from the poles toward the equator. This period, called the Marian Ice Age, lasted from about 651 million to 635 million years ago.
geoscientist at China University of Geosciences Huyue Song, said lead author of the research published in the journal Nature Communications.
Our study shows that, at least towards the end of the Marinoan ‘Snowball Earth’ event, habitable zones extended into the mid-latitude oceans, which are much larger than previously thought. Previous research has argued that such habitable zones, at best, existed. Only in tropical oceans. The more extensive habitable regions of the oceans best explain where and how complex organisms such as multicellular seaweeds survive.”
Song said the findings show that the world’s oceans were not completely frozen over and that habitable refuges existed where multicellular eukaryotes — the sphere of life including plants, animals, fungi and some single-celled organisms called protists — could survive.
Earth was formed about 4.5 billion years ago. The first single-celled organisms arose sometime during roughly the first billion years of the planet’s existence. Multicellular organisms arrived later, perhaps two billion years ago. But it was only in the aftermath of the Creogene that warmer conditions returned, setting the stage for a rapid expansion of various life forms some 540 million years ago.
Scientists are trying to better understand the onset of Snowball Earth. They believe that a significantly reduced amount of the Sun’s warmth reached the planet’s surface when solar radiation bounced off the white ice sheets.
“It is widely believed that carbon dioxide levels in the atmosphere declined just prior to these events, causing the polar ice caps to expand and thus more solar radiation to reflect back into space and the polar ice caps to expand further. , said Virginia Tech geobiologist and study co-author Shuhai Xiao.
Seaweeds and fossils of some other multicellular organisms have been identified in the black shale. This seaweed – a primitive plant – was a photosynthetic organism that lived on the sea floor in a shallow, sunlit marine environment.
“The fossils were preserved as compressed sheets of organic carbon,” said Chen Yi, a paleontologist at the China University of Geosciences and co-author of the study.
Multicellular organisms including red algae, green algae and fungi appeared before the Cryogenian and survived “Snowball Earth”.
The cryogenic freeze was much worse than the most recent ice age humans survived, ending nearly 10,000 years ago.
“Compared to the last Ice Age, the coverage of the glaciers was much more extensive, and more importantly, much of the ocean froze,” Xiao said.
“It’s fair to say that the ‘Earth Snowball’ events were great challenges for life on Earth,” Xiao added. “It is conceivable that these ‘snowball Earth’ events could have led to major extinctions, but life, including complex eukaryotes, appears to have managed to survive, demonstrating the resilience of the biosphere.”
(Reporting by Will Dunham; Editing by Rosalba O’Brien)
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