At the conclusion of the last global ice age, the Earth, which had been in a deep freeze, reached a natural threshold regarding climate change, resulting in a transition to a slushy environment. This research presents the first direct geochemical proof of this so-called ‘plume-world ocean’ period, when astronomically high levels of carbon dioxide forced the icy planet into a swift, extensive melting phase.
As the last global ice age came to a close, the frozen Earth eventually hit a natural limit regarding climate changes and transformed into a slushy realm.
A study led by Virginia Tech researchers reveals the first direct geochemical evidence for the slushy Earth — also referred to as the “plume-world ocean” era — when elevated carbon dioxide concentrations triggered a significant and rapid melting of the frozen planet.
According to the lead author, Tian Gan, who was a postdoctoral researcher at Virginia Tech, “Our findings have significant implications for understanding how Earth’s climate and ocean chemistry transformed following the extreme conditions of the last global ice age.” Gan collaborated with geologist Shuhai Xiao on the study, published on November 5 in the Proceedings of the National Academy of Sciences journal.
Deep-frozen Earth
The last global ice age occurred roughly 635 to 650 million years ago, which scientists think coincided with a drop in global temperatures and the advance of polar ice caps across the hemispheres. The expanding ice reflected a greater amount of sunlight away from the planet, leading to a vicious cycle of decreasing temperatures.
According to Xiao, who has recently been inducted into the National Academy of Sciences, “One-quarter of the ocean’s surface was frozen due to dramatically low carbon-dioxide levels.”
As the surface ocean froze over, various processes came to a halt:
- The water cycle became locked, resulting in no evaporation and minimal rain or snowfall.
- Due to the lack of water, a critical process known as chemical weathering — where rocks break down and erode — dramatically slowed down.
- This inactivity in weathering caused a buildup of carbon dioxide in the atmosphere, trapping heat.
Xiao remarked, “It was only a matter of time before carbon-dioxide levels climbed high enough to disrupt the ice pattern. When it concluded, it likely did so in a catastrophic manner.”
Plume world
Heat levels began to increase rapidly. As the ice caps started to withdraw, Earth’s climate shifted dramatically towards a wet and soupy condition. Over a span of just 10 million years, global temperatures fluctuated massively from minus 50 to 120 degrees Fahrenheit (minus 45 to 48 degrees Celsius).
However, the ice did not simply melt and mix with seawater at the same time. The research findings reveal a strikingly different scenario than one might envision: enormous streams of glacial meltwater surging from land to the ocean, accumulating atop saltier, denser seawater.
The researchers examined this ancient environment by studying a series of carbonate rocks that were created as the ice age drew to a close.
They looked at a specific geochemical marker, the levels of lithium isotopes, found in these carbonate rocks. The plume-world ocean theory predicts that the geochemical signals indicating freshwater would be more pronounced in rocks formed close to shore where meltwater collected than in rocks created offshore in the deep, saline ocean — and this is precisely what the researchers discovered.
The results clarify the limits of environmental change, according to Xiao, but also provide new insights into the resilience of life and biological frontiers in extreme conditions — whether hot, cold, or slushy.
Study collaborators include:
- Ben Gill, an associate professor of sedimentary geochemistry at Virginia Tech
- Morrison Nolan, a former graduate student now at Denison University
- 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
