Study explains what life was like on ‘Snowball Earth’ – 04/04/2023 – Science

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 frozen twice by runaway glaciation and looked like a bright white snowball from space.

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

Fossils identified as seaweed unearthed in black shale in central China’s Hubei province indicate that habitable marine environments at the time were vaster than previously known, scientists said Tuesday. The findings support the idea that it was more of a “Mud Ball Earth”, whose first forms of complex life – basic multicellular organisms – survived even in mid-latitudes thought to have been frozen solid.

The fossils date from the second of two times during the Cryogenic Period that massive ice sheets stretched from the poles towards the equator. This interval, called the Marinoan Glaciation, lasted from about 651 million to 635 million years ago.

“The main finding of this study is that there were open water —free ice—conditions in mid-latitude oceanic regions during the declining stage of the Marinoan Ice Age,” said Huyue Song, China University of Geosciences geobiologist, lead author. from research published in the journal Nature Communications.

“Our study shows that, at least towards the end of the Marinoan ‘Snowball Earth’ event, habitable areas extended into mid-latitude oceans, much larger than previously thought. Larger areas of habitable oceans better explain where and where how complex organisms such as multicellular algae survived,” added Song.

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

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

Scientists are trying to better understand the beginnings of “Snowball Earth”. They believe that a very small amount of heat from the Sun reached the planet’s surface when solar radiation bounced off the white ice sheets.

“It is generally believed that atmospheric carbon dioxide levels dropped shortly before these events, causing the polar ice caps to expand and therefore more solar radiation reflected back into space and the polar ice caps to expand further. And the Earth spiraled into snowball conditions,” said Virginia Tech geobiologist Shuhai Xiao, co-author of the study.

Algae and fossils of a few other multicellular organisms have been identified in black shale. This algae—a rudimentary plant—was a photosynthetic organism that lived on the seabed in a shallow, sunlight-lit environment.

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

Multicellular organisms, including red algae, green algae and fungi, arose before Cryogenics and survived “Snowball Earth”.

Cryogenic freezing was far worse than the most recent Ice Age humans survived, which ended about 10,000 years ago.

“Compared to the last Ice Age, the glacier cover was much more extensive and, more importantly, much of the ocean was frozen,” said Xiao.

“It’s fair to say that the ‘Snowball Earth’ events were significant challenges to life on Earth,” added Xiao. “It is conceivable that they caused major extinctions, but apparently life, including complex eukaryotic organisms, managed to endure, attesting to the resilience of the biosphere.”

^{Translated by Luiz Roberto M. Gonçalves}