Not snowball soil, extra of a slushball soil

Our planet wasn’t always the warm, welcoming place we know today. The earth has frozen at least five times in its history, caught in the grips of an ice age. Scientists sometimes refer to these periods as “Snowball Earths.” The common notion is that everything was covered in ice, making life difficult if not impossible. But there’s new evidence that during at least one of those icy periods, parts of the Earth’s surface may have been more like a giant squishy ball of mud.

Geologists study rock cores that contain material deposited on the sea floor during a period called the Marinoan Ice Age. It occurred about 635 million years ago during a geologic period aptly named the Cryogenian.

The Marinoan event was extreme. Over the course of 15 million years, it covered much of the planet with ice. “We called this ice age ‘Snowball Earth,'” said Thomas Algeo, a professor of geosciences in the College of Arts and Sciences at the University of Cincinnati and part of a team studying early Earth glaciation. “We believed that the earth was completely frozen during this long ice age. But maybe it was more of a ‘slushball earth’.”

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Recent evidence found in China changes this “snowball earth” view. Algeo is part of a team of geoscientists from China, the United Kingdom and the United States analyzing these rock cores. They discovered that the habitable conditions on the open sea during this period were more extensive than anyone had realized. This was true for oceans that lay between the tropics and the polar regions. These sites provided safe havens for unicellular and multicellular organisms during the waning stages of the Marinoan Ice Age.

Evidence for the slushball

Rock cores from this period show traces of a tiny algal organism called benthic phototropic macroalgae. It was there then and still exists on the seabed today. It is also a fundamental part of most ecosystems in which it exists, but it requires sunlight to convert water and carbon dioxide into energy through photosynthesis. The fact that it existed on Slushball Earth tells us it got the sunlight it needed. That suggests the oceans — or at least the shallower waters — weren’t completely frozen.

UC Geosciences Professor Thomas Algeo stands in front of rock cores that he and his students are analyzing in his lab. Photo/Andrew Higley/UC Marketing + Brand

Huyue Song of the China University of Geosciences and the first author of a paper on the mud-ball Earth, said while deep water probably didn’t contain oxygen to support life at that time, shallow seas did. “We present a new snowball model of Earth in which open waters existed in both the low- and mid-latitude oceans,” Song said, noting that the Ice Age likely experienced many periods of freezing and melting over a 15-million-year period had.

If that happened then it is very likely that life continued, especially in the shallow seas. “We found that the Marinoan Ice Age was dynamic. There may have been multiple potential open water conditions in the low and mid-latitudes,” Song said. “Furthermore, these surface water conditions may have been more widespread and persistent than previously thought, and may have enabled rapid biosphere recovery after the Marinoan Snowball Earth.”

Even tiny organisms can affect atmospheric changes

Interestingly, the existence of these macroalgae and other multicellular organisms may have played a role in both the beginning and end of this long-ago Ice Age. According to Algeo, the study of the Marinoan event raises questions about how other ice ages could have started.

An example of microalgae called Nannochloropsis to give an idea of ​​the type of organism in the slushball soil study. Courtesy of CSIRO.

For example, another icing later in the cryogenium likely covered much more of the planet. The question is what started it? “We don’t know exactly what triggered these ice ages, but I suspect it’s related to multicellular organisms removing carbon from the atmosphere, leading to carbon spillage and the cooling of the Earth,” Algeo said. “Today we are releasing carbon rapidly in large quantities and it is having a major impact on the global climate.”

The same life-form warming likely contributed to the end of the Marinoan, Algeo said. The thriving life in these shallow ocean regions released large amounts of carbon dioxide, which warmed the atmosphere and helped melt glaciers. “One of the overall takeaways is how much the biosphere can affect the carbon cycle and climate,” he said. “We know that carbon dioxide is one of the most important greenhouse gases. So we are seeing how changes in the carbon cycle are affecting global climate.”

History of the Ice Age

There have been five major ice ages in the history of the earth. The Huronium occurred 2.4 to 2.1 billion years ago. The Cryogenian spanned a period from 850 to 635 million years ago. The Andean Sahara occurred between 460 and 430 million years ago, while the Karoo formed between 360 and 260 million years ago. The most recent was in the Quaternary, spanning from 2.6 million years ago to the present. At least a dozen glaciations have occurred in the last million years, including what we often refer to as the “Ice Age.” It peaked nearly 20,000 years ago, covering thick sheets of ice across Canada, northern Europe, and parts of South America.

Scientists continue to explore the reasons why our planet has experienced these periodic coolings. There are many good theories about how ice ages begin and end, including atmospheric changes or a change in solar radiation. Studies like Huyue Song’s lend new weight to the role life may have played in the rise and fall of Earth’s ice periods.

For more informations

“Snowball Earth” might have been Slushball
Mid-latitude habitable environment for marine eukaryotes during the declining phase of the Marinoic snowball glaciation
The tonic and cryogenic period
Luminous light on benthic macroalgae: Mechanisms of complementarity in layered macroalgal assemblages

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