march 2, 2011 for science magazine
(http://www.sciencemag.org/news/2011/03/are-we-middle-sixth-mass-extinction)
earths creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the
dinosaurs. thats the conclusion of a new study, which calculates that three - quarters of todays animal
species could vanish within 300 years. his is really gloom - and - doom stuff,\ says the studys lead
author, paleobiologist anthony barnosky of the university of california, berkeley. \but the good news is
we havent come so far down the road that its inevitable.\
species naturally come and go over long periods of time. but what sets a mass extinction apart is that
three - quarters of all species vanish quickly. earth has already endured five mass extinctions, including the
asteroid that wiped out dinosaurs and other creatures 65 million years ago. conservationists have warned
for years that we are in the midst of a sixth, human - caused extinction, with species from frogs to birds to
tigers threatened by climate change, disease, loss of habitat, and competition for resources with nonnative
species. but how does this new mass extinction compare with the other five?
barnosky and colleagues took on this challenge by looking to the past. first, they calculated the rate at
which mammals, which are well represented in the fossil record, died off in the past 65 million years,
finding an average extinction rate of less than two species per million years. but in the past 500 years, a
minimum of 80 of 5570 species of mammals have gone extinct, according to biologists conservative
iestimates—an extinction rate that is actually above documented rates for past mass extinctions, says
barnosky. all of this means that were at the beginning of a mass extinction that will play out over
hundreds or thousands of years, his team concludes online today in nature. nature is a journal or
magazine that publishes some of the most popular recent findings by scientists.
the picture gets even grimmer when all mammals currently endangered or threatened are added to the
count. if those all disappear within a century, then by 334 years from now, 75% of all mammal species
will be gone, says barnosky. \look outside of your window. imagine taking away three - quarters of the
living things you see and ask yourself if you want to live in that world.\
the team extended the same methods of analysis to amphibians, reptiles, birds, plants, mollusks, and
other forms of life. they found fairly consistent patterns: from amphibians to birds to mammals, about
1% to 2% of species already are extinct today, and 20% to 50% are threatened—numbers that approach
those of the great mass extinctions of the past. \our best guess is that the current extinction rate is
between three to 80 times too high\ even without counting all threatened species, says barnosky.
\assuming threatened species would actually go extinct—which is not inevitable—puts the extinction
rate off the charts.\
heres been a lot of general talk on this issue, but attempts to draw more rigorously on the lessons of the
fossil record have been rare,\ says paleobiologist david jablonski of the university of chicago in illinois
who was not involved in the study. \its really valuable to look at how current losses stack up against the
past extinction events.\

Question

march 2, 2011 for science magazine
(http://www.sciencemag.org/news/2011/03/are-we-middle-sixth-mass-extinction)
earths creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the
dinosaurs. thats the conclusion of a new study, which calculates that three - quarters of todays animal
species could vanish within 300 years. 	his is really gloom - and - doom stuff,\ says the studys lead
author, paleobiologist anthony barnosky of the university of california, berkeley. \but the good news is
we havent come so far down the road that its inevitable.\
species naturally come and go over long periods of time. but what sets a mass extinction apart is that
three - quarters of all species vanish quickly. earth has already endured five mass extinctions, including the
asteroid that wiped out dinosaurs and other creatures 65 million years ago. conservationists have warned
for years that we are in the midst of a sixth, human - caused extinction, with species from frogs to birds to
tigers threatened by climate change, disease, loss of habitat, and competition for resources with nonnative
species. but how does this new mass extinction compare with the other five?
barnosky and colleagues took on this challenge by looking to the past. first, they calculated the rate at
which mammals, which are well represented in the fossil record, died off in the past 65 million years,
finding an average extinction rate of less than two species per million years. but in the past 500 years, a
minimum of 80 of 5570 species of mammals have gone extinct, according to biologists conservative
iestimates—an extinction rate that is actually above documented rates for past mass extinctions, says
barnosky. all of this means that were at the beginning of a mass extinction that will play out over
hundreds or thousands of years, his team concludes online today in nature. nature is a journal or
magazine that publishes some of the most popular recent findings by scientists.
the picture gets even grimmer when all mammals currently endangered or threatened are added to the
count. if those all disappear within a century, then by 334 years from now, 75% of all mammal species
will be gone, says barnosky. \look outside of your window. imagine taking away three - quarters of the
living things you see and ask yourself if you want to live in that world.\
the team extended the same methods of analysis to amphibians, reptiles, birds, plants, mollusks, and
other forms of life. they found fairly consistent patterns: from amphibians to birds to mammals, about
1% to 2% of species already are extinct today, and 20% to 50% are threatened—numbers that approach
those of the great mass extinctions of the past. \our best guess is that the current extinction rate is
between three to 80 times too high\ even without counting all threatened species, says barnosky.
\assuming threatened species would actually go extinct—which is not inevitable—puts the extinction
rate off the charts.\
	heres been a lot of general talk on this issue, but attempts to draw more rigorously on the lessons of the
fossil record have been rare,\ says paleobiologist david jablonski of the university of chicago in illinois
who was not involved in the study. \its really valuable to look at how current losses stack up against the
past extinction events.\

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