Earth’s climate has seen some big changes, from global volcanoes to ice ages cooling the planet and dramatic shifts in solar radiation. Yet life has continued, for the past 3.7 billion years, to strike.
Now, a study conducted by MIT researchers at Science advances He asserts that the planet contains a “stable feedback” mechanism that has been operating over hundreds of thousands of years to pull the climate back from the brink, keeping global temperatures within a constant habitable range.
Just how is this achieved? A possible mechanism is “silicate weathering”—a geological process that involves the slow, continuous weathering of silicate rocks in chemical reactions that eventually force carbon dioxide out of the atmosphere into ocean sediments, trapping the gas in the rocks.
Scientists have long suspected that silicate weathering plays a key role in regulating Earth’s carbon cycle. The silicate weathering mechanism could provide a geologically constant force in keeping carbon dioxide — and global temperatures — in check. But there has been no direct evidence of the ongoing operation of such comments, until now.
The new findings are based on a study of paleoclimate data that records changes in global average temperatures over the past 66 million years. The MIT team applied mathematical analysis to see if the data revealed any distinct patterns of stability of phenomena that limit global temperatures over a geological time scale.
They found that there indeed appears to be a consistent pattern in which Earth’s temperature fluctuations moderate over hundreds of thousands of years. The duration of this effect is comparable to the time scales over which silicate weathering is expected to act.
The results are the first to use actual data to confirm the existence of stabilizing reactions, the mechanism of which is likely to be silicate weathering. This feedback would explain how the Earth remained habitable through dramatic climatic events in the geological past.
“On the one hand, it’s a good thing because we know that global warming today will eventually be canceled out by these stabilization reactions,” says Konstantin Arnschedt, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “But on the other hand, it would take hundreds of thousands of years for that to happen, so it’s not fast enough to solve our current problems.”
The study was co-authored by Arnscheidt and Daniel Rothman, a professor of geophysics at MIT.
Scientists have previously seen hints of a climate-stabilizing influence in Earth’s carbon cycle: chemical analyzes of ancient rocks have shown that the flow of carbon into and out of Earth’s surface environment has remained relatively balanced, even through huge fluctuations in global temperature. Moreover, models of silicate weathering predict that the process should have some effect on global climate stability. Finally, the fact that Earth is habitable points to some geological test that is inherent in extreme temperature fluctuations.
“You have a planet whose climate has undergone many dramatic external changes. Why has life survived so long? One argument is that we need some kind of stabilization mechanism to maintain temperatures suitable for life,” says Arnscheidt. “But it is not proven from the data that such a mechanism has consistently controlled the Earth’s climate.”
Arnscheidt and Rothman sought to confirm whether stabilization feedback was indeed at work, by looking at data on global temperature fluctuations through geological history. They worked with a range of global temperature records collected by other scientists, ranging from the chemical composition of ancient marine fossils and shells, as well as ice cores preserved in the Antarctic.
“This entire study is only possible because there has been significant progress in improving the accuracy of deep-sea temperature records,” notes Arnschidt. “Now we have data going back 66 million years, with data points thousands of years apart.”
To the data, the team applied the mathematical theory of stochastic differential equations, which are commonly used to detect patterns in widely volatile datasets.
“We realized that this theory makes predictions of what you could expect from the Earth’s temperature history if there are feedbacks operating on certain time scales,” Arnscheidt explains.
Using this approach, the team analyzed the history of global average temperatures over the past 66 million years, considering the entire period over different timescales, such as tens of thousands of years versus hundreds of thousands, to see if any patterns of responses The sedentary act has appeared inside. on every schedule.
“In a sense, it’s like your car is accelerating down the street, and when you hit the brakes, you’re sliding for a long time before it comes to a stop,” says Rothman. “There is a time scale at which frictional resistance, or stable feedback, begins when the system returns to a steady state.”
Without feedback stabilization, global temperature fluctuations should increase with the timescale. But the team’s analysis revealed a system in which the fluctuations had not evolved, implying that a stabilizing mechanism prevailed in the climate before the fluctuations became too intense. The timescale for this proven effect—hundreds of thousands of years—coincides with what scientists would expect for the effect of weathering on silicates.
Interestingly, Arnscheidt and Rothman found that on longer time scales, the data revealed no stabilizing reactions. That is, there does not appear to be any recurring dip in global temperatures over time scales longer than a million years. Over these longer time scales, then, what has kept global temperatures in check?
“There is an idea that serendipity may have played a major role in determining why life still exists after more than 3 billion years,” says Rothman.
In other words, because Earth’s temperatures fluctuate over longer periods, these fluctuations may be small enough in a geological sense, to be within the range that stable feedbacks, such as silicate weathering, can maintain climate cyclically, and more than that, within a valid zone. for housing.
“There are two camps: some say random chance is a good enough explanation, others say there must be stable reactions,” says Arnschedt. “We are able to show, directly from the data, that the answer is probably somewhere in between. In other words, there was some stability, but it’s also possible that pure luck played a role in keeping Earth consistently habitable.”
This research was supported in part by a MathWorks Fellowship and the National Science Foundation.
By Jennifer Chu, MIT News Desk
The presence or instability of Earth system reactions on different time scales
The date the article was published
November 16, 2022
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