(Online Course) Contemporary Issues for IAS Mains 2012: Sci & Tech Issues – Has The Earth’s Sixth Mass Extinctional Ready Arrived.

Has The Earth’s Sixth Mass Extinctional Ready Arrived?

• With the steep decline in populations of many animal
  species, from frogs and fish to tigers, some scientists have warned that
  Earth is on the brink of a mass extinction like those that occurred only
  five times before during the past 540 million years.

• Each of these ‘Big Five’ saw three-quarters or more of
  all animal species go extinct.

• In a study published today (March 3) in Nature,
  University of California, Berkeley, paleobiologists assess where mammals and
  other species stand today in terms of possible extinction, compared with the
  past 540 million years, and they find cause for hope as well as alarm.

Risk of Extinction

• “If you look only at the critically end angered
  mammals—those where the risk of extinction is at least 50 per cent within
  three of their generations — and assume that their time will run out, and
  they will be extinct in 1,000 years, that puts us clearly outside any range
  of normal, and tells us that we are moving into the mass extinction realm,”
  said principal author Anthony D. Barnosky, UC Berkeley professor of
  integrative biology, a curator in the Museum of Paleontology and a research
  paleontologist in the Museum of Vertebrate Zoology.

• “If currently threatened species — those officially
  classed as critically endangered, endangered and vulnerable — actually went
  extinct, and that rate of extinction continued, the sixth mass extinction
  could arrive within as little as 3 to 22 centuries,” he said. Not too Late

• Nevertheless, Barnosky added, it’s not too late to save
  these critically end angered mammals and other such species and stop short
  of the tipping point. That would require dealing with a perfect storm of
  threats, including habitat fragmentation, invasive species, disease and
  global warming.

• “So far, only 1 to 2 per cent of all species have gone
  extinct in the groups we can look at clearly, so by those numbers, it looks
  like we are not far down the road to extinction. We still have a lot of
  Earth’s biota to save,” Barnosky said. “It’s very important to devote
  resources and legislation toward species conservation if we don’t want to be
  the species whose activity caused a mass extinction.”

• Coauthor Charles Marshall, UC Berkeley professor of
  integrative biology and director of the campus’s Museum of Paleontology,
  emphasized that the small number of recorded extinctions to date does not
  mean we are not in a crisis.

• “Just because the magnitude is low compared to the
  biggest mass extinctions we’ve seen in a half a billion years doesn’t mean
  to say that they aren’t significant,” he said.

• “Even though the magnitude is fairly low, present rates
  are higher than during most past mass extinctions.”

• “The modern global mass extinction is a largely
  unaddressed hazard of climate change and human activities,” said H. Richard
  Lane, program director in the National Science Foundation’s Division of
  Earth Sciences, which funded the research. “Its continued progression, as
  this paper shows, could result in unforeseen – and irreversible – negative
  consequences to the environment and to humanity.”

• The study originated in a graduate seminar Barnosky
  organized in 2009 to bring biologists and paleontologists together in an
  attempt to compare the extinction rate seen in the fossil record with
  today’s extinction record. These are “like comparing apples and oranges,”
  Barnosky said. For one thing, the fossil record goes back 3.5 billion years,
  while the historical record goes back only a few thousand years. In
  addition, the fossil record has many holes, making it is impossible to count
  every species that evolved and subsequently disappeared, which probably
  amounts to 99 per cent of all species that have ever existed. A different
  set of data problems complicates counting modern extinctions.

• Dating of the fossil record also is not very precise,
  Marshall said.

• “If we find a mass extinction, we have great difficulty
  determining whether it was a bad weekend or it occurred over a decade or
  10,000 years,” he said. “But without the fossil record, we really have no
  scale to measure the significance of the impact we are having.”

• To get around this limitation, Marshall said, “This
  paper, instead of calculating a single death rate, estimates the range of
  plausible rates for the mass extinctions from the fossil record and then
  compares these rates to where we are now.”

• Mammals were chosen as a starting point as they are well
  studied and well represented in the fossil record going back some 65 million
  years. Biologists estimate that within the past 500 years, at least 80
  mammal species have gone extinct out of a starting total of 5,570 species.

• The team’s estimate for the average extinction rate for
  mammals is less than two extinctions every million years, far lower than the
  current extinction rate for mammals.

• “It looks like modern extinction rates resemble mass
  extinction rates, even after setting a high bar for defining ‘mass
  extinction,’” Barnosky said.

• After looking at the list of threatened species
  maintained by the International Union for Conservation of Nature (IUCN), the
  team concluded that if all mammals now listed as ‘critically endangered,’ ‘
  endangered’ and ‘threatened’ go extinct, whether that takes several hundred
  years or 1,000 years, Earth will be in a true mass extinction.

• “Obviously there are caveats,” Barnosky said. “What we
  know is based on observations from just a very few twigs plucked from the
  enormous number of branches that make up the tree of life.”

• “Our findings highlight how essential it is to save
  critically endangered, endangered and vulnerable species,” Barnosky added.
  If most of them die, even if their disappearance is stretched out over the
  next 1,000 years, the  sixth mass extinction will have arrived.” —
  University of California, Berkeley

Go Back To Main Page