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Roughly 34 million years ago, the Earth started transitioning from a greenhouse to an icehouse state — defined by long-term cooling trends that resulted in ice sheets in the planet’s polar regions. During this time, continental carbon reservoirs expanded as carbon dioxide decreased in the atmosphere.

But that trend has reversed. Fossil fuel consumption, among other sources of pollution, have resulted in increasing atmospheric and oceanic temperatures, leading to ice sheet melt and unprecedented shifts in our environments. 

New research from an international team of scientists suggests that these recent, rapid warming conditions exist within a larger climatic pattern — one that has been persistently driven by extraterrestrial forcing. 

“The phase that we’re in, the more mature phase of the icehouse, is one that’s more sensitive,” said study co-author , a Distinguished Professor in the Department of Earth and Planetary Science, housed in the College of Letters and Science at UC Davis. “Any small change could have a larger effect on the carbon-climate dynamics, as  it is a more susceptible system.”

In a , researchers reveal that the climate trajectories experienced during the Late Cenozoic Ice Age (34 million years ago to present day) are consistent with those seen during the Late Paleozoic Ice Age (340 to 280 million years ago), the last time the Earth was dotted with glaciers. 

Through analysis of deep-water sediments, the researchers found evidence of paired shifts in carbon cycling and climate. These shifts occurred during both our present icehouse and the penultimate one 300 million years ago and were caused by extraterrestrial forcing — specifically cyclical variations in the Earth’s orbit and tilt called Milankovitch cycles.  

“This is truly the first time anyone has shown that regardless of the appearance of the planet — whether the continents are in a big mass or spread across the globe as they are today, or there are dinosaurs or there are forests specifically like those that exist today — the Earth is highly tuned to extraterrestrial forcing, and it’s been that way for hundreds of millions of years,” Montañez said. “But humans can still mess with it really quickly.”

Extraterrestrial influences on the Earth’s climate

The study hinged on the analysis of sediment cores from ancient deep-water sources in China. Montañez said it’s rare to find such pristine deep-water sediments due to the continuous shift of the Earth’s tectonic plates, which can disrupt the makeup of the sediments and thus the geological record. 

“But these are really well-studied and well-dated,” she said of the sediment cores analyzed in the study. “They’re a beautiful archive and provide the best template for these types of studies.” 

The team analyzed 5,000 geochemical datapoints from 1,782 sediment samples. The gamma-ray values and carbon isotopes in the sediments enabled the team to discern the influence of the Earth’s orbit and tilt on the planet’s climate-carbon cycles and icehouse conditions during the Late Paleozoic Ice Age.      

Using the data, the team pinpointed a period, some 307 million years ago, when the type of influence that extraterrestrial forcing had on the Earth’s climate shifted. Up until that point, the Earth was cooling with carbon reservoirs on land increasing. After 307 million years ago, the trend reversed. 

This same scenario played out in the icehouse we currently live in 6 million years ago, suggesting that the Earth is in the mature phase of its current glaciated state. 

“We had a 37 million-year-long record of evidence of extraterrestrial forcing and it allowed us to test and confirm a lot of the modeling we did earlier — the ecosystem modeling and the climate modeling,” Montañez said. “We could interpret that it was a strong planetary force.”  

Montañez said that throughout the Earth’s Milankovitch cycles, the planet’s wobble and tilt shift on scales of tens of thousands of years. Shifts in the Earth’s orbit happen over hundreds of thousands of years.

“Because of the Earth’s wobble and shape of our orbit around the sun, we can have more intense summers and more intense winters, or less,” Montañez said. “When you have ice houses and the land is vegetated, this extraterrestrial forcing is a big player.”

The dangers of throwing off the Earth’s balance

While the study highlights the significant and persistent extraterrestrial influence on the Earth’s climate-carbon cycle, Montañez emphasized that humans must be diligent when it comes to mitigating our effects on the climate. We still play a critical role, with our choices influencing the planet. 

This includes changes caused by humans, like increased carbon dioxide emissions.

Montañez likened our planet to a canoe on the water. Both exist in a state of balance. They may wobble or tilt depending on external and internal conditions, but they exist in a state of equilibrium. 

“The Earth system is so perfectly tuned that it doesn’t care if it was 300 million years ago or if it was the last 30 years,” Montañez said.

Throw in a wrench, like anthropogenic pollution, and conditions change further. In other words, the canoe can tip over and sink.

“As we’ve shown previously for the Late Paleozoic Ice Age, when you mess with warmth, you can make your shallow oceans anoxic enough that your fisheries would die out,” Montañez said. “The Earth system is amazing, but we are perturbing that system.” 

Additional co-authors include Qiang Fang, Huaichun Wu, Shu-zhong Shen, Christian Zeeden, Xiangdong Wang, Shihong Zhang and David De Vleeschouwer. The research was cosponsored by the National Natural Science Foundation of China, the Fundamental Research Funds for the Central Universities and the Chinese “111” project.