New evidence rewrites Ice Age history

New evidence suggests that the Marinois Ice Age, one of the most severe ice ages in Earth’s history, may not have completely frozen the planet as previously thought. Instead, it was more of a “Slush Land” with patches of open water supporting life in the shallow mid-latitude seas. The discovery, published in Nature Communications, is based on geological samples and ancient algae over 600 million years old.

Geologists have found evidence that the planet did not experience complete glaciation during the Ice Age, which occurred 635 million years ago.

The earth has experienced at least five ice ages, one of which occurred 635 million years ago, resulting in glaciers stretching from one pole to the other. This particular ice age, known as the Marinoian Ice Age, takes its name from the region in Australia where the first geological evidence was discovered in the 1970s.

The Marinois Ice Age is regarded by scientists as one of the worst in Earth’s history, resulting in glacial ice that persisted for a staggering 15 million years.

But new data collected in the eastern forest region of Shennonjia, China’s Hubei province, suggests that the Earth was not completely frozen – at least not by the end of the Ice Age. Instead, some shallow mid-latitude seas had patches of open water, based on geological patterns from that period.

“We called this Ice Age Snowball Earth,” said Thomas Algeo, professor of geosciences at the University of Cincinnati College of Arts and Sciences. “We believed that the Earth completely froze over during this long ice age. But perhaps it was more like “Slush Land”.

Researchers have found evidence that the Earth was not completely frozen during the Marinian Ice Age 635 million years ago. Shallow seas in the middle latitudes remained free of ice, which may have contributed to the preservation of life. Credit: Michael Miller

The study was published in the journal Nature Communications.

Scientists have discovered benthic phototrophic macroalgae in black shale over 600 million years old. These algae live on the bottom of the sea and need sunlight to convert water and carbon dioxide into energy through photosynthesis.

A team of geologists from China, the UK and the US conducted an isotope analysis and found that habitable conditions in the open ocean are more extensive than previously thought, extending into oceans located between the tropics and polar regions and providing a haven for unicellular and multicellular organisms on a waning stages of the Marino Ice Age.

University of Cincinnati geology professor Thomas Algeo and his co-authors have found isotopic evidence that some mid-latitude seas remained ice-free during the Marinoan Ice Age, known as Snowball Earth. Credit: Andrew Higley

Lead author Huyue Song of the China University of Geosciences said that while the deep water probably did not contain oxygen to sustain life during this period, the shallow waters did.

“We are introducing a new Snowball Earth model where open water existed in both low and mid-latitude oceans,” Song said.

Song said the ice age likely saw many freeze and melt intervals over a period of 15 million years. And under these conditions, life could survive, Sun said.

“We found that the Marinoian glaciation was dynamic. There may have been potential open water conditions at low and mid-latitudes several times,” Song said. “In addition, these conditions in surface waters may have been more common and more persistent than previously thought, and may have allowed the biosphere to quickly recover from Marinoan Snowball Earth.”

University of Cincinnati geology professor Thomas Algeo examines rock cores in his lab. Credit: Andrew Higley

Ironically, according to Algeo of the University of California, these sanctuaries of life likely helped warm the planet, ending the Marinoan Ice Age. The algae in the water released carbon dioxide into the atmosphere over time, gradually melting the glaciers.

“One of the general findings to take home is how much the biosphere can influence the carbon cycle and climate,” he said. “We know that carbon dioxide is one of the most important greenhouse gases. So we see how changes in the carbon cycle affect the global climate.”

Algeo said the study raises tantalizing questions about other ice ages, especially the second during the cryogenic period, which scientists believe also resulted in a near-total glaciation of the planet.

“We don’t know exactly what caused these ice ages, but I suspect it was due to multicellular organisms removing carbon from the atmosphere, which led to carbon storage and cooling of the Earth,” Algeo said. “Today, we are rapidly releasing carbon in massive amounts, and this is having a big impact on the global climate.”

Reference: Habitable Environment for Marine Eukaryotes at Mid-Latitudes During the Waning Stage of the Marino Snowball Glaciation by Huyue Song, Zhihui An, Qin Ye, Eva E. Stüeken, Jing Li, Jun Hu, Thomas J. Algeo, Li Tian, ​​Daoliang Chu, Haijun Song, Shuhai Xiao, and Jinnan Tong, April 4, 2023, Nature Communications.
DOI: 10.1038/s41467-023-37172-x

The study was funded by the National Natural Science Foundation of China and the Geological Survey of China.