New evidence suggests that the Marinoan Ice Age, one of Earth's most severe ice ages, may have not completely frozen the planet as previously assumed. Instead, it was more of a "Slushball Earth," with patches of open water supporting life in the shallow mid-latitude seas, according to the publication.
Earth has gone through at least five ice periods, one of which occurred 635 million years ago, which resulted in glaciers spanning from one pole to the other. This particular Ice Age, named the Marinoan Ice Age, comes from Australia's central region where the first geological evidence was discovered in the 1970s.
Scientists believe the Marinoan Ice Age to be one of Earth's most severe Ice Ages, leading to the formation of glacial ice that lasted for a staggering 15 million years.
According to geologic samples dating back to that period, the Earth was not completely frozen in the Shennongjia Forestry District in China's Hubei Province.
"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."
Evidence from scientists that Earth was not completely frozen solid during the Marinoan ice age 635 million years ago
The research has been published in the journal Nature Communications.
In black shale, scientists discovered benthic phototrophic macroalgae that date back more than 600 million years. This algae lives at the bottom of the sea and requires sunlight to convert water and carbon dioxide to energy through photosynthesis.
A team of geoscientists from China, the United Kingdom, and the United States performed an isotopic analysis and concluded that habitable open-ocean conditions were more widespread than previously assumed, including oceans that fall between the tropics and the polar regions as well as providing refuge for single-celled and multi-celled organisms during the final stages of the Marinoan ice age.
Thomas Algeo, a professor of geography at the University of Cincinnati, and his co-authors discovered isotopic evidence that some mid-latitude seas remained ice-free during the Marinoan Ice Age known as Snowball Earth. Credit: Andrew Higley
Huyue Song, an author at the China University of Geosciences, said that although deep water likely did not contain oxygen to support life during this period, shallow seas did.
Song said. "We propose a new Snowball Earth model in which open waters existed in both low- and mid-latitude oceans."
Song believes that over the span of 15 million years, life might have persisted.
"We found that the Marinoan glaciation was dynamic. There may have been various open-water conditions in the low and middle latitudes," Song said. "These conditions in surface waters may have been more widespread and more sustainable than previously assumed, and may have allowed a rapid recovery of the biosphere following the Marinoan Snowball Earth."
Thomas Algeo, a geophysicist at the University of Cincinnati, performs a study in his lab. Credit: Andrew Higley
According to UC's Algeo, these living sources may have helped to warm the planet, putting an end to the Marinoan ice age. Over time, the algae in the water released carbon dioxide into the atmosphere, gradually melting the glaciers.
"We know that carbon dioxide is one of the most important greenhouse gases," said the speaker. "We see how changes in the carbon cycle have an effect on the global climate."
Algeo said the research raises alarming questions about other ice ages, particularly the second one during the Cryogenian Period, which scientists believe contributed to near-total global glaciation.
"We don't know for sure what triggered these ice age, but my suspicion is that it was multicellular organisms that removed carbon from the atmosphere, leading to carbon burial and the cooling of the Earth," Algeo said. "Today, we're releasing carbon rapidly in huge quantities and it's having a big impact on global climate."
Huyue Song, Zhihui An, Eva E. Stüeken, Jing Li, Jun Hu, Thomas J. Algeo, Li Tian, Daoliang Chu, Haijun Song, Shuhai Xiao, and Jinnan Tong, 4 April 2023, Nature Communications. DOI: 10.1038/s41467-023-37172-x
The China Geological Survey and the National Natural Science Foundation provided funding for the research.
