It will take the Earth 3 million years to recover from the species going extinct in the near future
This is utter nonsense. To make such a claim, you have to have a firm count of how many species there already are plus an equally firm count of the number of species that existed on at least one occasion in the past. No such counts exist. So it is all just guessing.
And in any case extinctions have always happened, sometimes on a massive scale. On some estimates, 95% of all the species that have ever lived on earth are now extinct. We don't grieve that the once ubiquitous trilobites are no more so it would seem normal to accept the reality of death and extinction. But given the modern-day efforts at nature conservation, it is entirely open to us to conclude that extinctions actually have slowed down in the modern era. LOL
Note that a lot of the extinctions we know about were from the pre-modern or early modern era, not the product of 20th and 21st century civilization: The mammoth, the dodo and the passenger pigeon, for instance. And the extinction of the Australian megafauna appears to date from the arrival of Aborigines in Australia, who were pretty good hunters of slow animals -- and that was about 50,000 years ago -- so definitely not the fault of modern man
And note the implicit assumption that the non-extinction of all animals is good. Why is it good? I think we could make a case that it does not matter at all -- excerpt perhaps for sentimental reasons. The possibility that some one or other of the existing animals might do us some unknown good in the future would have to be vanishingly small at this stage of our knowledge. We don't allow for all the possibilities in our lives -- or else we would never do anything
Humans will cause so many mammal species to go extinct in the next 50 years that the planet's evolutionary diversity won't recover for 3 to 5 million years, a team of researchers has found.
The Earth may be entering its sixth mass extinction: an era in which the planet's environments change so much that most animal and plant species die out. The International Union for the Conservation of Nature predicts that 99.9% of critically endangered species and 67% of endangered species will be lost within the next 100 years.
The five other times a mass extinction has occurred over the past 450 million years, natural disasters were to blame. But now, human activity is killing mammal species.
In a study published Monday in the journal PNAS, scientists from Aarhus University in Denmark calculated how fast extinctions are happening, and how long it would take for evolution to bring Earth back to the level of biodiversity it currently has.
The scientists concluded that in a best-case scenario, nature will need 3-5 million years to get back to the level of biodiversity we have on Earth today. Returning to the state Earth's animal kingdom was in before modern humans evolved would take 5-7 million years.
Evolution can't keep up
Evolution is the planet's defense mechanism against the loss of biodiversity. As habitats and climates change, species that can't survive die, and new species slowly emerge. But it takes a long time for new species to fill the gaps — and that process is far slower than the rate at which humans are causing mammals to go extinct.
For their calculations, the Aarhus University researchers used a database containing existing mammal species and mammals that already went extinct as humans spread across the planet. They combined that data with information about extinctions expected to come in the next 50 years, and used advanced simulations of evolution to predict how long recovery would take.
Their estimates are based on an optimistic assumption that people will eventually stop ruining habitats and causing species to die out, and the extinction rate will go back down. But even in that best-case scenario, the timeline depends on how quickly mammals start recovering. If the extinction rate doesn't start falling for another 20-100 years, more species will likely disappear, causing greater diversity loss, the study said.
The researchers noted that in their model, certain species were given more importance than others. Matt Davis, a paleontologist at Aarhus University who led the study, cited the shrew as an example. There are hundreds of species of shrew, so if one or two go extinct, that would not kill off all shrews on Earth.
But there were only four species of sabre-toothed tigers on the planet. So when they all went extinct, many years of evolutionary history disappeared with them.
"Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct," Davis said in a press release. "Since they had few close relatives, their extinctions meant that entire branches of Earth's evolutionary tree were chopped off."
Today, other large animals like the black rhino are facing extinction. Asian elephants' chance of making it to the 22nd century is less than 33%, the study found. These elephants are one of only two remaining species from a group of mammals that once included mastodons and mammoths.
"We now live in a world that is becoming increasingly impoverished of large wild mammalian species," Jens-Christian Svenning, an Aarhus University professor who researches megafauna, said in the press release. "The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly."
He noted that the planet no longer boasts giant beavers, giant deer, or giant armadillos.
Though the researchers' findings are dire, the scientists said their work could be used to figure out which endangered species are evolutionarily unique, which might help conservationists decide where to focus their efforts to prevent the most devastating extinctions.