Hostile to life in 250 million years?

In the distant future, Earth’s land masses could merge into a supercontinent characterized by ultra-hot deserts. © University of Bristol

How will plate tectonics change the Earth and its living conditions in the distant future? A model simulation now predicts that there will be a threat of deadly heat in around 250 million years: Extremely hot climatic conditions could prevail on the supercontinent Pangea Ultima, which is predicted for this time, which hardly offers mammals any chance of survival.

Landmasses collided and separated again: Through the processes of plate tectonics, the Earth has continuously changed its face throughout its history - and this will continue. Currently the land masses are relatively widely spread across the planet. But it wasn't always like this: it is believed that they once merged into a supercontinent called Pangea. About 200 million years ago, this structure broke apart and its parts drifted into their present positions. But what will happen next?

Based on the current movements of the tectonic plates, researchers believe that the continents are heading towards unification again. Accordingly, a new supercontinent, known as Pangea Ultima, will have emerged in about 250 million years. The plate teckonic “fast forward” is always associated with an uncertainty factor. However, the models indicate a high probability that the gigantic landmass will form in the equatorial region and will hardly reach higher latitudes on earth.

What conditions might exist on Pangea Ultima?

An international team of researchers has now used model simulations to investigate the question of what conditions could prevail on the future supercontinent. They took different influencing factors into account: The calculations included estimates of how the location of the supercontinent and the landmass, which is hardly interrupted by water areas, would affect climate conditions. The scientists also implemented probable changes in the carbon dioxide content of the atmosphere as well as forecasts of the intensity of the Earth's irradiation from the sun in 250 million years.

As the team reports, based on assumed developments, extremely hot conditions are emerging on Pangea Ultima. Accordingly, increased volcanism as the supercontinent forms will lead to enormous carbon dioxide emissions. The atmospheric content could therefore reach twice the current value and thus lead to an enormous greenhouse effect. A 2.5 percent higher radiation intensity from the sun would also contribute to warming. All of this, in turn, could affect a landmass located primarily in the tropical region of the Earth. “The newly formed supercontinent would create a triple whammy that includes the effect of landmass, the hotter sun and more CO2 in the atmosphere,” says lead author Alexander Farnsworth from the University of Bristol. As a result, a large part of the land area would probably be confronted with temperatures between 40 and 70 degrees Celsius,” says the researcher.

Harmful to land mammals

But what would that mean for life? For this question, the team focused on assessing the impact on mammals, which therefore also includes a possible future form of humans. This group of creatures has so far been able to adapt extremely well to very different temperature conditions on Earth: In addition to cold tolerance, the mammals have also developed mechanisms for adapting to heat. But there are upper limits that can hardly be expanded through evolutionary adaptations.

Based on today's heat tolerance, the conditions predicted by the researchers on Pangea Ultima would hardly provide any habitat for land mammals. Due to heat, lack of water and the loss of food sources, only between 8 and 16 percent of the land area could ultimately allow them to survive, according to the model simulations. This would probably lead to an enormous wave of extinctions, say the scientists.

However, as they point out, there is a difference to today's developments in the context of climate change. The current rapid warming can also cause mass extinctions and, in some areas of the world, lead to the climatic tolerance ranges being exceeded. Given today's continental configuration, the majority of Earth's land masses will, in principle, remain habitable, even in the face of severe global warming. However, in the world that could exist in 250 million years, this would not be the case.

Astrobiological significance

In principle, however, it is important to note in the study that the look into the distant future is based on assumptions about developments. There could also be alternative developments within the framework of plate tectonics, which could result in other continental configurations. It also seems unclear how life on earth - including humans - will develop in the enormous period of 250 million.

However, the study fundamentally illuminates the possible development of living conditions on our planet. Finally, Farnsworth also looks at the universe: The results show the importance of tectonics and continental layouts when assessing exoplanets. “Whether a world within the so-called habitable zone of a star system offers life-friendly conditions on land may also depend on whether continents are scattered or whether there is a large supercontinent,” says Farnsworth.

Source: University of Bristol, specialist article: Nature Geoscience, doi: 10.1038/s41561-023-01259-3

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