Life on our planet faced a stern test during the Cryogenian Period that lasted from 720 million to 635 million years ago when Earth twice was frozen over with runaway glaciation and looked from space like a shimmering white snowball.
Life somehow managed to survive during this time called “Snowball Earth,” and a new study offers a deeper understanding as to why.
Fossils identified as seaweed unearthed in black shale in central China’s Hubei Province indicate that habitable marine environments were more widespread at the time than previously known, scientists said on 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 at mid-latitudes previously thought to have been frozen solid.
The fossils date from the second of the two times during the Cryogenian Period when massive ice sheets stretched from the poles toward the equator. This interval, called the Marinoan Ice Age, lasted from about 651 million to 635 million years ago.
“The key finding of this study is that open-water – ice-free – conditions existed in mid-latitude oceanic regions during the waning stage of the Marinoan Ice Age,” said China University of Geosciences geobiologist Huyue Song, lead author of the research published in the journal Nature Communications
“Our study shows that, at least near the end of the Marinoan ‘Snowball Earth’ event, habitable areas extended to mid-latitude oceans, much larger than previously thought. Previous research argued that such habitable areas, at best, only existed in tropical oceans. More extensive areas of habitable oceans better explain where and how complex organisms such as multicellular seaweed survived,” Song added.
The findings demonstrate that the world’s oceans were not completely frozen and that habitable refuges existed where multicellular eukaryotic organisms – the domain of life including plants, animals, fungi and certain mostly 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 roughly the first billion years of the planet’s existence. Multicellular organisms arrived later, perhaps 2 billion years ago. But it was only in the aftermath of the Cryogenian that warmer conditions returned, paving the way for a rapid expansion of different life forms about 540 million years ago