Life survived on 'snowball Earth,' scientists tell why

Though it is beyond our normal perception of time, Earth took millions and millions of years to develop life. It went through hardships before becoming the globe-spanning phenomenon it is now. One such phase came during the Cryogenian period that lasted from 720 million to 635 million years ago. During this time, Earth was a frozen sphere which may have looked like a shimmering snowball from space. Frozen conditions create difficulties in the development of a thriving life but life found a way nonetheless.

A new study has thrown light on how life was able to survive in spite of difficult conditions.

This period is also called "Snowball Earth"

Scientists found fossilised seaweed that was unearthed in black shale in China's Hubei province. Based on their observations scientists think that habitable marine environments were more widespread on "Snowball Earth" than previously thought.

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.