250 million is the new 40: mammals may already be halfway there on Earth, study finds

We can say this about mammals: we've had a good run.

In the 250 million years since the first mammals separated from reptiles and birds, we hairy, warm-blooded vertebrates have come to dominate the Earth, along with rodents, humans, ungulates and whales living on almost every square inch of the planet.

But the end of that reign could come much sooner than traditionally thought, suggests a new study published this week in the journal Natural geosciences.

Scientists have long believed that life on Earth will continue until the planet enters its “runaway greenhouse” phase, a state in which water vapor and other greenhouse gases present in the atmosphere becomes so dense that heat cannot escape from the surface and the oceans evaporate. , like the planet Venus. It's in 2 or 3 billion years.

Mammals will encounter problems much sooner because of our limited ability to resist heat, the study concludes. Our mechanisms for preventing overheating — like sweat, circulatory systems and the ability to physically move to cooler environments — can only go so far, and evolution can only go so fast, Alexander said. Farnsworth, climate researcher at the University of Bristol and lead author. on the study.

Ultimately, “the Earth could reach a tipping point making it uninhabitable for mammalian life,” the researchers wrote.

The study puts the end date of mammals in about 250 million years, roughly the same amount of time since they first appeared.

It is difficult to predict what the planet will look like in such a long time; For comparison, modern humans have only been around for about 50,000 years and have dramatically changed the planet in that time.

Farnsworth and his colleagues nevertheless describe three major factors that will increase temperatures on Earth.

The big one: a future supercontinent. Throughout Earth's history, continents have experienced a cycle of converging into supercontinents and then dispersing into separate continents, as we see today. Predictions suggest that the next cycle will bring together our current continents into a supercontinent, called Pangea Ultima, centered along the equator.

“Instead of having continents scattered across the world, they now all inhabit most of the tropics. And, of course, we know that the tropics are a very, very hot and humid place to live. So this is already going to have a big impact,” Farnsworth said.

Added to this will be a surge of volcanic activity, according to the study. Historically, supercontinents have coincided with an increase in volcanism that will release more carbon dioxide into the atmosphere – perhaps double the current amount, researchers predict.

And meanwhile, as the sun ages, it will emit more energy – about 1% more every 100 million years – adding even more heat to the equation.

In total, Farnsworth said, much of the supercontinent would have average monthly temperatures above “40, 50 or even 60 degrees centigrade” — the equivalent of 104, 122 or 140 degrees Fahrenheit.

“It’s not going to be a very pleasant place for most species,” he said.

Perhaps only 8% of Earth will be habitable for mammals, according to the study. And competition will be tough for these plots of habitable land – which would be located primarily on the borders of what is currently Canada, Russia and Chile. Reptiles could reemerge as the dominant type of life, or birds could win out.

The best hope for mammal survival during the Pangea Ultima era on Earth may resemble the North African gerbil, he said, a small rodent that thrives in the harsh conditions of the Sahara Desert. “It doesn’t need too much humidity, too much water or too much food,” he said. “Who knows? Maybe they radiate outward and mammals re-evolve from those lineages into something new.