The Permian-Triassic extinction event, also called The Great Dying, certainly earned its nickname. It was the largest mass extinction in geological records, wiping out between 83 and 97% of all living species on Earth. Although the exact cause is debated, extreme volcanic activity that may have baked the planet has been singled out as the main culprit.
But somehow, despite being hammered by asteroids and space radiation, life on this planet has continued for almost four billion years. As our planet enters a sixth mass extinction, driven by a wave of human activity that has wiped out thousands of species, the question of how it works – in particular, how Earth seems to be bouncing back from large-scale disasters scale or extreme changes in the atmosphere or climate — becomes even more pressing.
It turns out that the answer may, in part, be even stranger than anyone imagined. New research in the journal Science Advances suggests the Earth can self-regulate its temperature over hundreds of thousands of years. In other words, there are large-scale geological processes that seem to absorb carbon dioxide over enormous time scales. However, the timescales involved are far, far too long to correct for the sudden spike in carbon dioxide caused by the burning of fossil fuels, meaning the mechanism will not save us from climate change.
“You have a planet whose climate has been subjected to so many dramatic external changes. Why has life survived all this time?”
Constantin Arnscheidt and Daniel Rothman, two researchers at the Massachusetts Institute of Technology in Cambridge, analyzed data from several datasets documenting global temperature over the past 66 million years. These paleoclimate records include ice cores from Antarctica and the chemical composition of prehistoric marine fossils, which can tell us a lot about what Earth’s atmosphere was like in the distant past.
“This whole study is only possible because there have been great strides in improving the resolution of these deep sea temperature records,” Arnscheidt said in a statement. “Now we have data going back 66 million years, with data points at most thousands of years apart.”
The two MIT scientists found a strong pattern suggesting that Earth uses feedback loops to keep its temperatures within a range where life can thrive. However, this is happening on a time scale over hundreds of thousands of years, so even if it means our planet will rebound from anthropogenic climate change, it won’t happen soon enough to save us.
“One argument is that we need some sort of stabilization mechanism to maintain temperatures suitable for life,” Arnscheidt said. “But such a mechanism has never been shown from data to consistently control Earth’s climate.”
This finding has big implications for our understanding of the past, but also for how global warming is shaping the future of our homeworld. It even helps us better understand the evolution of planetary temperatures, which can make the search for exoplanets inhabited by extraterrestrials more fruitful.
“You have a planet whose climate has been subjected to so many dramatic external changes. Why has life survived all this time? One argument is that we need some kind of stabilization mechanism to maintain temperatures fit for life,” Arnscheidt said. “But such a mechanism has never been shown from data to consistently control Earth’s climate.”
Many scientists have proposed that the Earth has self-regulated its temperature throughout history, but this has been difficult to prove. In the 1960s, the late inventor and ecologist James Lovelock applied Darwinian processes to the entire planet, rather than a single organism, to explain how such a complex system evolved. He called it the Gaia hypothesis, which explains how Earth and its biological systems have formed feedback loops that keep our planet friendly to living organisms.
It also helped explain the weak sun paradox, first proposed by astronomers Carl Sagan and George Mullen in 1972. Essentially, our Sun was much smaller and cooler 4.5 billion years ago. At the time, based on our current understanding of the life cycle of stars, the Sun would have been about 30% dimmer than it is today. This in turn would have made the Earth too cold for liquid water, preventing life from forming – but it obviously happened. So how did our rocky world pull this off?
The answer seems to lie in how carbon is cycled across the planet. One prominent theory is that when our planet first formed it had an atmosphere full of carbon dioxide, a potent greenhouse gas, which allowed it to absorb heat, even though the Sun was more cold.
“On the one hand, it’s good because we know that today’s global warming will eventually be canceled thanks to this stabilizing feedback. But on the other hand, it will take hundreds of thousands of years to produce, so not fast enough to solve our current – day-to-day problems.”
A complex process known as silicate weathering then removes carbon dioxide from the atmosphere and buries it at the bottom of the ocean. Over time, this cools the planet. Then something like major volcanic eruptions or humans driving cars pump more carbon dioxide into the air, warming the planet again. Over the eons, Earth seems to be in balance between too cold and too hot, which is why some call Earth a Goldilocks planet.
The MIT study helps match existing data with this long-standing theory, helping us better understand our past and the consequences of runaway climate change. And it would make sense that if these feedback loops exist on our planet, they could also exist in other galaxies, informing the hunt for extraterrestrial life.
“On the one hand, it’s good because we know that the current global warming will eventually be canceled thanks to this stabilizing feedback,” says Constantin Arnscheidt, graduate student in the Department of Earth, Atmospheric and Planetary Sciences. (EAPS) from MIT. “But on the other hand, it will take hundreds of thousands of years, so not fast enough to solve our current problems.”
However, Arnscheidt’s model was unable to account for this balance on time scales greater than a million years, so chance may also have played an outsized role in the success. of life on this rock.
“There are two camps: some say chance is sufficient explanation, and others say there must be stabilizing feedback,” Arnscheidt said. “We are able to show, directly from the data, that the answer is probably somewhere in between. In other words, there has been some stabilization, but sheer luck probably also played a role. in keeping the Earth permanently habitable.”
It may be a mix of randomness and feedback loops like silicate weathering that influenced Earth’s temperature in the past. But in the future of humanity, it will be free will – our politics, our consumption, our choices – that will determine the temperature of the planet in the future. And we could overwhelm these natural systems so much that they won’t be able to balance each other, much like the important theories about potential life on Mars.
“The heating of the Sun was slow enough to allow life to evolve, a process that takes millions of years. Unfortunately, the Sun is now too hot for the further development of organic life on Earth,” wrote Lovelock in his 2019 book “Novacene: The Coming Age of Hyperintelligence.” “Our star’s heat output is too great for life to begin again as it did from the simple chemicals of the Archean period between 4 billion and 2.5 billion years ago. If life on Earth is wiped out, it will not start again.”
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