Study explains how primordial life survived on ‘Snowball Earth’

WASHINGTON, April 4 (Reuters) – Life on our planet faced a severe test during the Cryogenic Period, which lasted from 720 million to 635 million years ago, when Earth was twice frozen by runaway glaciers and appeared from space as a sparkling white snowball.

Life somehow managed to survive during this time called “Snowball Earth,” and a new study offers a deeper understanding of why.

Fossils identified as seaweed discovered in black shale in central China’s Hubei province show that habitable marine environments were more widespread at the time than previously known, scientists said Tuesday. The findings support the idea that it was more of a “Slushball Earth” where the earliest forms of complex life — basic multicellular organisms — endured even in mid-latitudes previously thought to be frozen.

The fossils date from the second of two times 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 – conditions existed in mid-latitude oceanic regions during the decline phase of the Marinoan Ice Age,” said China University of Geosciences geobiologist Huyue Song, lead author of research. published in the journal Nature Communications.

“Our study shows that, at least near the end of the Marinoan Snowball Earth event, habitable zones extended into the mid-latitude oceans, much larger than previously thought. Previous research argued that such habitable zones, at best, they only existed in the tropics. Wider areas of habitable oceans better explain where and how complex organisms like multicellular seaweeds survived,” Song added.

The findings show that the world’s oceans were not completely frozen and that habitable shelters existed where multicellular eukaryotic organisms — the domain of life including plants, animals, fungi and some mostly single-celled organisms called protists — could survive, Song said.

Earth was formed approximately 4.5 billion years ago. The first single-celled organisms appeared sometime during the first billion years of the planet’s existence. Multicellular organisms came later, perhaps 2 billion years ago. But it was only after the Cryogen that warmer conditions returned, paving the way for a rapid expansion of various life forms around 540 million years ago.

Scientists are trying to better understand the beginning of “Snowball Earth”. They believe that a greatly reduced amount of the sun’s heat reached the planet’s surface as solar radiation bounced off the white layers of ice.

“It is widely believed that atmospheric carbon dioxide levels fell slightly before these events, causing the polar ice caps to expand and thus more solar radiation reflected back into space and the polar ice caps expanded further,” said the geobiologist of Virginia Tech and study co-author Shuhai Xiao.

Seaweed and fossils of several other multicellular organisms were identified in the black shale. This seaweed – a rudimentary plant – was a photosynthetic organism that lived on the bottom of the sea in a shallow marine environment illuminated by sunlight.

“The fossils were preserved as compressed sheets of organic carbon,” said China University of Geosciences paleontologist and study co-author Qin Ye.

Multicellular organisms including red algae, green algae and fungi emerged before the Cryogen and survived on “Snowball Earth”.

The cryogenic freeze was much worse than the last ice age that humans survived, ending roughly 10,000 years ago.

“Compared to the most recent ice age, the ice cover was much more extensive and, more importantly, most of the ocean was frozen,” Xiao said.

“It is fair to say that the ‘Snowball Earth’ events were significant challenges to life on Earth,” Xiao added. “It is conceivable that these ‘Snowball Earth’ events may have caused major extinctions, but apparently life , including complex eukaryotic organisms, managed to survive, testifying to the persistence of the biosphere.”

Reporting by Will Dunham, Editing by Rosalba O’Brien

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