A recent Virginia Tech-led study provides the first direct geochemical evidence of the 'plumeworld ocean' era, when high carbon dioxide levels forced the frozen Earth into a massive, rapid melting period. The study, released on November 5 in the Proceedings of the National Academy of Sciences journal, was conducted by lead author Tian Gan, a former Virginia Tech postdoctoral researcher, and geologist Shuhai Xiao.
"Our results have important implications for understanding how Earth's climate and ocean chemistry changed after the extreme conditions of the last global ice age," said Tian Gan, according to Mirage News.
The last global ice age occurred approximately 635 million to 650 million years ago. Previous studies revealed that something froze the Earth for 57 million years. During this period, the growing ice reflected more sunlight away from the Earth, initiating a spiral of plunging temperatures. Scientists believe that global temperatures dropped, and the polar ice caps began to extend around the hemispheres.
"A quarter of the ocean was frozen due to extremely low carbon-dioxide levels," said Shuhai Xiao, according to Phys.org. Global cooling halted the processes of carbon dioxide absorption, causing carbon dioxide to gradually accumulate in the atmosphere and retain heat. At some point, the concentration of carbon dioxide became sufficient to trigger the melting of the ice. "It was just a matter of time until the carbon-dioxide levels were high enough to break the pattern of ice," explained Xiao, according to Science Daily.
Over a mere 10 million years, average global temperatures swung dramatically from minus 50 to 120 degrees Fahrenheit (minus 45 to 48 degrees Celsius). Suddenly, heat started to build after the last global ice age, leading to a rapid change in Earth's climate toward a warmer, wetter state as the ice caps began to recede. "When it ended, it probably ended catastrophically," Xiao added, according to Mirage News.
The findings suggest a very different world than what is commonly imagined: vast rivers of glacial water rushing like a reverse tsunami from the land into the sea, then pooling on top of extra salty, extra dense ocean water. Fresh water collected on top of the super-dense and very salty seawater, creating a slushy planet completely covered with slush and mud for a time. Analysis of carbonate rocks showed that during this time, the Earth's surface was filled with huge rivers of glacial water flowing from the land to the ocean, similar to a reversed tsunami.
When the surface ocean sealed during the last global ice age, a chain of reactions stuttered to a stop, resulting in no evaporation and very little rain or snow. Without water, there was a massive slowdown in a carbon-dioxide-consuming process called chemical weathering, where rocks erode and disintegrate.
The researchers tested this version of the prehistoric world by examining a set of carbonate rocks that formed as the global ice age was ending. They analyzed the relative abundance of lithium isotopes recorded within the carbonate rocks. According to plumeworld ocean theory, the geochemical signatures of freshwater would be stronger in rocks formed under nearshore meltwater than in the rocks formed offshore, beneath the deep, salty sea. The researchers observed that the geochemical signatures of freshwater were indeed stronger in rocks formed under nearshore meltwater, confirming the theory.
"The findings bring the limit of environmental change into better focus," said Xiao, according to Gazeta.ru. The research provides additional insight into the frontiers of biology and the resiliency of life under extreme conditions—hot, cold, and slushy.
Study collaborators include Ben Gill, Virginia Tech associate professor of sedimentary geochemistry; Morrison Nolan, former graduate student now at Denison University; and collaborators from the Chinese Academy of Sciences, University of Maryland at College Park, University of Munich in Germany, University of North Carolina at Chapel Hill, and University of Nevada at Las Vegas.
Sources: Mirage News, Phys.org, Science Daily, Gazeta.ru
This article was written in collaboration with generative AI company Alchemiq