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"Snowball Earth’ may not have been frozen solid

New evidence collected from the eastern Shennongjia Forestry District of China’s Hubei Province suggests that the Earth was not completely frozen during the Marinoan Ice Age, 635 million years ago, as previously thought. 

While the ice age, one of the most extreme in Earth’s history, created glaciers from pole to pole and persisted for 15 million years, new findings suggest that there were patches of open water in some of the shallow mid-latitude seas.

“We called this ice age ‘Snowball Earth,’” said Thomas Algeo, a professor of Geosciences at the University of Cincinnati’s College of Arts and Sciences. “We believed that Earth had frozen over entirely during this long ice age. But maybe it was more of a ‘Slushball Earth.’”

The study was published in the journal Nature Communications and led by Huyue Song from the China University of Geosciences, with contributions from researchers from the United Kingdom and the United States. 

The researchers found benthic phototrophic macroalgae in black shale dating back more than 600 million years, which requires light from the sun to convert water and carbon dioxide into energy through photosynthesis. They conducted an isotopic analysis and found that habitable open-ocean conditions were more extensive than previously thought, extending into oceans that fall between the tropics and the polar regions and providing refuge for single-celled and multi-celled organisms during the waning stages of the Marinoan ice age.

“We present a new Snowball Earth model in which open waters existed in both low- and mid-latitude oceans,” said Song. “We found that the Marinoan glaciation was dynamic. There may have existed potential open-water conditions in the low and middle latitudes several times. In addition, these conditions in surface waters may have been more widespread and more sustainable than previously thought and may have allowed a rapid rebound of the biosphere after the Marinoan Snowball Earth.”

The study raises intriguing questions about other ice ages, particularly the second one during the Cryogenian Period that scientists also believe created near-total glaciation of the planet. Algeo speculates that multicellular organisms might have triggered these ice ages by removing carbon from the atmosphere, leading to carbon burial and the cooling of the Earth. 

Today, humans are releasing carbon quickly in huge amounts, which is having a significant impact on global climate.

“One of the general take-home messages is how much the biosphere can influence the carbon cycle and climate,” Algeo said. “We know that carbon dioxide is one of the most important greenhouse gases. So we see how changes in the carbon cycle have an impact on the global climate.”

Paradoxically, the refuges of life in the open waters during the Marinoan Ice Age likely helped to warm the planet and end the ice age, as the algae in the water released carbon dioxide into the atmosphere over time, gradually thawing the glaciers.

The study was supported by grants from the National Natural Science Foundation of China and the China Geological Survey. The findings suggest that life can persist under extreme conditions, and it is crucial to understand the impact of the biosphere on the Earth’s climate.

Other theories about ‘Snowball Earth’

The Snowball Earth hypothesis is a theory that proposes that the Earth was once entirely covered in ice and snow for millions of years, possibly around 650 million years ago. The theory is based on geological evidence and is supported by various lines of evidence, including sedimentary deposits, glacial features, and isotope records.

There are several theories as to what could have caused the Snowball Earth event. One theory suggests that a drop in atmospheric carbon dioxide (CO2) levels could have triggered the onset of global glaciation. This could have occurred due to a decrease in volcanic activity, which reduces the amount of CO2 released into the atmosphere, or due to the weathering of rocks, which consumes CO2 through chemical reactions.

Another theory suggests that the Earth’s position in the solar system could have played a role. The amount of solar radiation that the Earth receives is controlled by several factors, including the tilt of the Earth’s axis and the shape of its orbit. It is possible that a combination of these factors caused a decrease in solar radiation, leading to global cooling and the onset of glaciation.

A third theory suggests that a series of large volcanic eruptions could have caused the Snowball Earth event. These eruptions would have released large amounts of volcanic gases, including sulfur dioxide and ash, into the atmosphere. This would have blocked sunlight and caused a cooling effect, which could have triggered global glaciation.

Despite the many theories about what caused the Snowball Earth event, scientists still do not have a clear answer. The debate continues, with researchers using a variety of methods, including computer simulations and laboratory experiments, to try to better understand the conditions that led to this unique period in Earth’s history.

Regardless of the cause, the Snowball Earth event had a profound impact on the evolution of life on Earth. The extreme cold and lack of sunlight would have made it very difficult for most organisms to survive, and many species may have gone extinct. However, the survivors would have had to adapt to extreme conditions, leading to the evolution of new and unique forms of life.

What is an ice age?

An ice age is a long period of time, usually lasting thousands of years, during which the Earth’s climate is significantly colder than usual. These cold periods are marked by the growth of massive ice sheets, glaciers, and sea ice, which cover much of the Earth’s surface.

Ice ages are caused by a complex interplay of factors, including variations in the Earth’s orbit and the amount of solar radiation it receives, changes in the distribution of land masses, and fluctuations in atmospheric and oceanic circulation. During an ice age, temperatures can drop by several degrees Celsius, and large portions of the planet become uninhabitable for most species.

Despite their name, ice ages are not marked by a continuous period of freezing temperatures. Instead, they are characterized by a series of cycles of glacial advances and retreats, during which ice sheets and glaciers grow and shrink in response to changing climate conditions.

The last major ice age, known as the Last Glacial Maximum, occurred between 26,000 and 19,000 years ago, when large portions of North America, Europe, and Asia were covered in ice. Since then, the Earth’s climate has warmed significantly, and we are currently living in a warm interglacial period.

Although ice ages may seem like a distant and ancient phenomenon, they have had a profound impact on the history of life on Earth, shaping the evolution of species and influencing the development of human civilizations. Understanding the causes and effects of ice ages is therefore essential for understanding the complex dynamics of our planet’s climate system.


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