'Without Doubt,' a Sixth Mass Extinction Event is Here
No, it isn't the End of Days, but we are likely living during what experts will later refer to as one of the largest extinction events in Earth's history - an unexpected addition to prehistory's "Big Five" mass extinctions.
That's at least according to an international team of researchers who argue that modern history "shows without any significant doubt that we are now entering the sixth great mass extinction event."
"There are examples of species all over the world that are essentially the walking dead," investigator Paul Ehrlich, a Bing Professor of Population Studies in biology and a senior fellow at the Stanford Woods Institute for the Environment, said in a statement. (Click here to jump to a video on the results!)
Extinction is Everyday. Mass Extinction is Not.
Ehrlich, who has researched mass extinctions since the writing of his 1981 book, Extinction: The Causes and Consequences of the Disappearance of Species, admitted that "extinction goes on all the time" and is a natural part of the ever-changing world.
However in five (possibly six) moments in Earth's prehistoric past, extinction became so prevalent and so wide-spread across the globe that it changed the course of evolution forever. For instance, about 252 million years ago, a suspected "perfect storm" of dooms-day scenarios including disease, massive volcanic eruptions, and even you obligatory asteroid impact resulted in the extinction of 90 percent of all marine species and 70 percent of all land animals. This came to be known as "the Great Dying," and is the second most recognizable of the Big Five mass extinctions. (Scroll to read on...)
The most recent and iconic of those five, the Great Impact, occurred about 66 million years ago and is a better example for what characterizes a mass extinction event. This event, which wiped the dinosaurs (and a surprising number of mammals) from the Earth, wound up eliminating anywhere from half to two-thirds of all known plant and animal life. Fish, surprisingly, survived to inherit the ocean, resulting in the undersea world we see today. You can read about that here.
What you can see from these two examples - and the three (or four) others like it - is that a mass extinction occurs when a singificant portion of plant and animal life across the entire Earth dies off in a short period of time, relative to the multi-billion year age of the Earth.
Mass Extinction in the Modern Age
To see how noteworthy the current rate of extinction around the world is, Ehrlich and his colleagues decided to look to the fossil record, decades and decades of biological data, and past species extinction studies.
Past work had already revealed what they similarly found. A 2014 study published in the esteemed journal Science found that since the year 1500, more than 320 terrestrial vertebrates have become extinct. Likewise, as of the study's conclusion, 16 to 33 percent of all species were estimated to be globally threatened or endangered.
Soon after, another paper published in Nature found that 41 percent of all amphibians on the planet now face extinction, while 26 percent of mammal species and 13 percent of birds are similarly threatened. (Scroll to read on...)
Ehrlich and his colleagues add to these findings, looking to recent extinctions that have already happened. According to their work, which was published in the journal Science Advances, even "extremely conservative" estimates say that species are currently disappearing about 100 times faster than normally seen between mass extinctions - called the background rate.
And this, amazingly, is even after the researchers accounted for an adjusted background rate - after a 2011 study headed by Berkley researchers determined that the background rate for mammals specifically is twice as fast as once thought.
"It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining 'mass extinction,'" Anthony D. Barnosky, a research paleontologist and the principle author of the study, explained in a past statement.
Specifically he and his colleagues estimated that within the past 500 years, at least 80 mammal species have gone extinct out of a starting total of 5,570 species. Comparatively the average extinction rate for mammals is less than two extinctions every million years. (Scroll to read on...)
[ Credit: Stanford University ] Back to top.
Ehrlich adds that his new paper is "basically the icing on the cake" of that already substantial argument, showing verified and bolstered data about the current rate of extinction.
"If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on," said lead author Gerardo Ceballos, of the Universidad Autónoma de México.
"We emphasize that our calculations very likely underestimate the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity's impact on biodiversity," the researchers added.
That is to say, they wanted to consider natural causes alongside the undeniable role land development, the introduction of invasive species (via shipment, pets, etc), man-made carbon emissions, and pollution have played in the extinction of species.
"Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations."
And if that doesn't work, perhaps some other intelligent species will look back millions of years from now and call this time "The Mankind Event" - the newest member of 'The Big Six.'
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