Study identifies 6th mass extinction event, lists human activity as primary cause

After years of warnings from ecologists about the dangers of biodiversity loss, a new study has quantified an ongoing mass extinction event — the sixth in our planet’s history — and suggests humans are largely to blame.

The paper, published June 19 in the journal Science Advances, takes a “conservative” approach to measuring the extent of the situation because previous estimates have been criticized for overestimating the severity of the extinction crisis.

The primary researchers — from institutions such as UC Berkeley, Stanford University and the National Autonomous University of Mexico — compared current extinction rates with a normal baseline rate of two mammal extinctions per 10,000 vertebrate species per 100 years. Based on this measure, about nine vertebrate species should have disappeared from the earth since 1900. But the paper’s “conservative” extinction count stands at 477, which should have taken as many as 10,000 years to occur.

Paul Ehrlich, senior fellow at the Stanford Woods Institute for the Environment and co-author of the study, notes that the species extinction rate is the highest it has been in 65 million years.

“We’re essentially doing to the planet what the meteor did that took care of the dinosaurs,” he said of the data’s implications.

Seth Finnegan, an assistant professor in UC Berkeley’s integrative biology department who specializes in mass extinction, said the researchers’ study contrasts with other studies that tend to estimate modern extinction rates indirectly. For example, some measure areas of destroyed habitats and then extrapolate extinction predictions based on how many species are believed to exist in those areas.

“This study doesn’t take the inferential approach,” he said. “They are tallying up well-documented, well-observed extinctions of mammals.”

Though extinction can occur because of a variety of environmental factors, the study emphasizes humans’ effect on the alarming rate of species loss. According to Finnegan, industrialization has “drastically accelerated humans’ impact on Earth’s ecosystems.”

Co-author Anthony Barnosky, a campus professor of integrative biology, cited a high per-capita use of fossil fuels and the over-exploitation of ecosystems for economic gain as major contributing factors.

“In one or two human lifetimes, we are the ones wiping out what evolution took millions of years to create,” he said.

In addition to being the driving force behind the sixth mass extinction, humans will ultimately face “high moral and aesthetic costs” in as little as three lifetimes, according to Barnosky. Crucial ecosystem services, such as crop pollination and water purification, will suffer if high rates of extinction persist, the study says.

Considering that it took up to millions of years for the planet to rediversify after the previously recorded mass extinctions, the study says, these consequences would be effectively permanent on human time scales.

Ehrlich said that some conservation efforts could potentially slow the process of mass extinction but said he agrees with the study’s conclusion that “the window of opportunity is rapidly closing.”

“Conservation biologists are hard at work trying to stop it,” he said. “But there’s not a hope of changing this in the long run if human populations keep increasing and we maintain a pattern of perpetual growth on a finite planet.”

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Big Five mass extinction events

Although the Cretaceous-Tertiary (or K-T) extinction event is the most well-known because it wiped out the dinosaurs, a series of other mass extinction events has occurred throughout the history of the Earth, some even more devastating than K-T. Mass extinctions are periods in Earth's history when abnormally large numbers of species die out simultaneously or within a limited time frame. The most severe occurred at the end of the Permian period when 96% of all species perished. This, along with K-T, are two of the Big Five mass extinctions, each of which wiped out at least half of all species. Many smaller scale mass extinctions have occurred, indeed the disappearance of many animals and plants at the hands of man in prehistoric, historic and modern times will eventually show up in the fossil record as mass extinctions. Discover more about Earth's major extinction events below.

Ordovician-Silurian mass extinction

The third largest extinction in Earth's history, the Ordovician-Silurian mass extinction had two peak dying times separated by hundreds of thousands of years. During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number.


Late Devonian mass extinction

Three quarters of all species on Earth died out in the Late Devonian mass extinction, though it may have been a series of extinctions over several million years, rather than a single event. Life in the shallow seas were the worst affected, and reefs took a hammering, not returning to their former glory until new types of coral evolved over 100 million years later.

Permian mass extinction

The Permian mass extinction has been nicknamed The Great Dying, since a staggering 96% of species died out. All life on Earth today is descended from the 4% of species that survived.

Triassic-Jurassic mass extinction

During the final 18 million years of the Triassic period, there were two or three phases of extinction whose combined effects created the Triassic-Jurassic mass extinction event. Climate change, flood basalt eruptions and an asteroid impact have all been blamed for this loss of life.

Cretaceous-Tertiary mass extinction

The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs.