But new evidence collected in the Shennongjia Forest District in eastern China’s Hubei province suggests that the Earth was not completely frozen – at least not until the end of the Ice Age. Instead, there were shallow seas, based on geological samples dating back to that time.
“We called this ice age ‘Snowball Earth'”said Thomas Algeo, Professor of Geosciences at the College of Arts and Sciences of the University of Cincinnati, USA. “I thought the Earth was completely frozen during this long ice age. But maybe it was more of a ‘Snowball Earth’.”
Macroalgae for over 600,000 million years
Scientists have found macroalgae in black shale dating back more than 600 million years. This algae lives on the bottom of the sea and needs light from the sun to convert water and carbon dioxide into energy through photosynthesis.
A team of geologists from China, Britain and the United States carried out an isotopic analysis and found that all conditions for habitability in the open ocean were more generous than previously thought, with the oceans located between the tropics and polar regions and providing refuge for single-celled organisms and pluricellular during the declining stages of the ice age.
“We present a new snowball Earth model in which liquid water existed in both the shallow and mid-depth oceans”said lead author Huyue Song of the China University of Geosciences.
Song said the ice age probably saw several freeze-thaw intervals over the course of 15 million years. And under these conditions, life could have persisted. “We found that the Marinoan glaciation was dynamic. It is possible that there have been several times potential water conditions at shallow or medium depths”, concludes the expert.
Paradoxically, Algeo believes, these refuges of life probably helped warm the planet, ending the Marinoan Ice Age. The algae in the water released carbon dioxide into the atmosphere over time, gradually thawing the glaciers. “One of the general messages to remember is how much the biosphere can influence the carbon cycle and climate. We know that carbon dioxide is one of the most important greenhouse gases. Therefore, we see how changes in the carbon cycle have an impact on the global climate”.
Algeo said the study raises tantalizing questions about other ice ages, particularly the second, which scientists also believe created a near-total glaciation of the planet. “We don’t know for sure what triggered these ice ages, but my guess is that an important role is played by multicellular organisms that removed carbon from the atmosphere, which led to the carbon being ‘buried’ and the Earth cooling.”Algeo said. “We are currently releasing carbon rapidly and in huge amounts, and this is having a huge impact on the global climate,” concludes the specialist.
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