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.”
What’s happening to honey
bees?
What happens if all bees die?
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.
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. 
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. 
