WASHINGTON, April 4 (Reuters) – Life on our planet faced a severe test during the Cryogenian Period that lasted from 720 million to 635 million years ago when Earth froze twice with runaway glaciation and look from space like a twinkling white snowball.
Life has somehow survived this period called “Snowball Earth,” and a new study offers a deeper understanding of why.
Fossils identified as seaweed unearthed from black shale in Central China’s Hubei Province indicate that habitable marine environments were more widespread at the time than previously known, scientists said Tuesday. The findings support the idea that this is more than just a “Slushball Earth” where the earliest forms of complex life – basic multicellular organisms – endured even in mid-latitudes once thought to be frozen solid.
The fossils come from the second of two times during the Cryogenian Period when massive ice sheets stretched from the poles to the equator. This interval, called the Marinoan Ice Age, lasted from 651 million to 635 million years ago.
“The main finding of this study is that open-water – ice-free – conditions existed in mid-latitude ocean regions during the waning phase of the Marinoan Ice Age,” said the Chinese geobiologist University of Geosciences Huyue Song, lead author of the research. published in the journal Communication in Nature.
“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. The previous research has argued that such habitats, at best, exist only in tropical areas. oceans. The wider ocean habitats better explain where and how complex organisms such as multicellular seaweed,” Song added.
The findings show that the world’s oceans were not completely frozen and habitable shelters existed where multicellular eukaryotic organisms – the domain of life including plants, animals, fungi and some mostly single -celled organisms called protists – can survive, Song said.
Earth was formed approximately 4.5 billion years ago. The first single-celled organisms appeared sometime in the first billion years of the planet’s existence. Multicellular organisms came 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 about 540 million years ago.
Scientists are trying to better understand the origin of “Snowball Earth.” They believe that very little of the sun’s heat reaches the planet’s surface as solar radiation bounces off the white ice.
“It is widely believed that carbon dioxide levels in the atmosphere fell prior to these events, causing the polar ice caps to expand and therefore more solar radiation to reflect back into space and the polar ice caps further expanded. And the Earth rotated in Snowball Earth conditions,” said Virginia Tech geobiologist and study co-author Shuhai Xiao.
Seaweed and fossils of several other multicellular organisms have been identified in the black shale. This seaweed – a rudimentary plant – is a photosynthetic organism that lives on the sea floor in a shallow marine environment lit 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 appeared before the Cryogenian and survived on “Snowball Earth.”
The Cryogenian freeze was worse than the last Ice Age that humans lived in, which ended about 10,000 years ago.
“Compared to the last Ice Age, the glacier range was much wider and, more importantly, most of the ocean was frozen,” Xiao said.
“It is fair to say that ‘Snowball Earth’ events are significant challenges to life on Earth,” Xiao added. “It is conceivable that these ‘Snowball Earth’ events could have caused mass extinctions, but it seems that life, including complex eukaryotic organisms, survived, proving the resilience of the biosphere.”
Reporting by Will Dunham, Editing by Rosalba O’Brien
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