[ti:Study Explains How Life Survived the 'Snowball Earth' Period]
[al:Science & Technology]
[ar:VOA]
[dt:2023-04-17]
[by:www.voase.cn]
[00:00.00]Life on Earth faced an extreme test of survivability during the Cryogenian Period, which began 720 million years ago.
[00:13.75]The planet was frozen over most of the 85 million-year period.
[00:22.44]Scientists say Earth would have looked like a shiny white snowball in space during the deep freeze.
[00:32.99]But life somehow survived during this time called "Snowball Earth." 
[00:39.39]A recent study offers a deeper understanding as to why.
[00:46.19]Fossils identified as seaweed were found in black shale, a kind of rock, in central China's Hubei Province.
[00:58.10]The scientists said the fossils are a sign that livable water environments were more widespread at the time than they once believed.
[01:12.04]Nature Communications published the research this month.
[01:17.88]The findings support the idea that the planet was more of a "Slushball Earth" with melting snow. 
[01:27.90]This enabled the earliest forms of complex life to survive in areas once thought to have been frozen solid.
[01:39.34]The fossils date from the second of the two times during the Cryogenian Period when ice sheets stretched from the poles toward the equator. 
[01:52.33]This period, called the Marinoan Ice Age, lasted from about 651 million to 635 million years ago.
[02:05.16]Huyue Song of the China University of Geosciences was the study's lead investigator and writer.
[02:15.60]The researcher said the most important finding was that ice-free, open water conditions existed in place during the last part of the Marinoan Ice Age.
[02:31.78]"More extensive areas of habitable oceans better explain where and how complex organisms such as multicellular seaweed survived," Song said.
[02:47.55]The findings demonstrate that the world's oceans were not completely frozen.
[02:54.11]It means areas of habitable refuge existed where multicellular organisms could survive, the scientist added.
[03:05.42]Earth formed about 4.5 billion years ago.
[03:12.22]The first single-celled organisms appeared in the first billion years of the planet's existence.
[03:20.51]Multicellular organisms arrived later, maybe two billion years ago.
[03:27.96]But it was only after the Cryogenian period that warmer conditions returned. 
[03:35.53]That helped drive a quick expansion of different life forms about 540 million years ago.
[03:46.11]Scientists are trying to better understand the start of "Snowball Earth." 
[03:53.15]They believe a greatly reduced amount of the sun's warmth reached the planet's surface as its radiation bounced off the white ice sheets.
[04:06.34]Seaweed and fossils of some other multicellular organisms were identified in the black shale.
[04:16.08]This seaweed was a photosynthetic organism living on the seafloor in a shallow sea environment lit by sunlight.
[04:27.45]"The fossils were preserved as compressed sheets of organic carbon," said researcher Qin Ye, also of China University of Geosciences.
[04:42.40]Multicellular organisms including red algae, green algae and fungi appeared before the Cryogenian and survived "Snowball Earth."
[04:57.28]The Cryogenian freeze was much worse than the most recent Ice Age that humans survived. 
[05:06.60]It ended about 10,000 years ago.
[05:11.00]I'm Caty Weaver.