What it tells us
rather clearly is that the Permian extinction was a protracted geological event
unlike Yucatan which produced instant change.
The rising heat content of surface waters need to also be understood better. That should have produced an explosion of
biological complexity.
I personally
suspect that the traps produced so much Sulphur on a continuing basis as to
shift global surface water acidity to such an extreme as to make life
impossible except in fortunate refugia.
Once the threshold had been crossed, it would take the cessation of
extreme volcanism to allow the acids to be worked out of the water column. This would have made survival difficult for
all life.
The nature of
rock weathering from the era may turn out to be distinct and should be
investigated. The rain itself would
often carry dilute Sulphuric Acid and would preferentially attack surfaces.
It Took 60,000
Years to Kill Nearly Everything on Earth
By Becky Oskin, Staff Writer |
February 10, 2014 03:00pm ET
It took only 60,000 years to kill more than 90
percent of all life on Earth, according to the most precise study yet of the
Permian mass extinction, the greatest die-off in the past 540 million years.
The new timeline doesn't reveal the culprit behind
the die-off, though scientists have several suspects, such as volcanic
eruptions in Siberia that belched massive quantities of climate-changing gases.
But pinning down the duration of the Permian mass
extinction will help
researchers refine its potential trigger mechanisms, said Seth Burgess, lead
study author and a geochemist at MIT.
"Whatever caused the extinction was really
rapid, or the biosphere reached some critical threshold," Burgess told
Live Science. "Having an accurate timeline for the events surrounding the
mass extinction and the interval itself is extremely important, because it
gives us an idea of how the biosphere responds."
The findings were published today (Feb. 10) in the
journal Proceedings of the National Academy of Sciences.
Radioactivity and extinctions
The Permian mass extinction marks the end of the
Permian geologic period, which ended approximately 252 million years ago. More
than 96 percent of marine life and 70 percent of land species perished. By
comparison, 85 percent of life died off during the dinosaur-killing extinction
at the end of the Cretaceous period, 66 million years ago. [Wipe Out:
History's Most Mysterious Extinctions]
"This is one of the fundamental inflection
points in the trajectory of life on Earth," Burgess said. "It set the
stage for the [rest] of evolution."
The best record of the Permian
"great dying" is in
Meishan, China. In past decades, hundreds of geologists collected and analyzed
rocks in Meishan that date from before, during and after the Permian
extinction. Researchers analyzed these rocks to better understand what caused
the Permian event. Volcanic ash beds interlaced with Meishan marine rocks have
tiny minerals called zircons that can be precisely dated with geochemical
techniques, and the marine rocks carry scores of fossils that record the
die-off and resurgence of life.
Burgess and his co-authors improved the Meishan rock
ages with the latest high-resolution, uranium-lead zircon dating techniques.
Zircon traps minute amounts of naturally occurring radioactive uranium inside
its crystal structure. Uranium decays into lead, and counting the ratio of the
two elements provides an age estimate for the zircons.
The new dates show that the mass extinction started
251.941 million years ago (plus or minus 37,000 years) and ended at 251.880
million years ago (plus or minus 31,000 thousand years). The extinction's end
also marks the start of the Triassic period, and coincides with the first fossil appearance at
Meishan of a toothy, eel-like creature called Hindeodus parvus (a
conodont, the source of the earliest teeth found in the fossil record).
Finding the killer(s)
The new timeline also provides greater accuracy for
the environmental blows linked with the mass dying. For example, previous work
has found an increase in carbon dioxide, a greenhouse gas, before the mass extinction began. In the Permian
rocks, atmospheric carbon dioxide shifts are recorded as changes in the ratio
of carbon isotopes.
The new study suggests the increase in carbon
dioxide was sudden and short-lived, Burgess said. "It precedes the
extinction by 20,000 years or so, and lasts 10,000 or 15,000 years. It was very
short-duration event," he said.
But there are other potential tipping points for extinction
beyond atmospheric greenhouse gases. For example, sea surface temperatures also
rose about 18 degrees Fahrenheit (10 degrees Celsius) over a period beginning
before the extinction and continuing into the early Triassic. And the sudden
carbon dioxide increase may have made the oceans more acidic. (A similar effect
is happening in the present age due to carbon dioxide concentrations that have
been rising because of man-made sources since the 1850s.)
"An accurate and high-precision age model gives
us a reliable sounding [board] against which we can start comparing all of the
other things that started happening with the mass extinction," Burgess
said.
The research team is now applying the same
age-dating technique to one of the main Permian mass extinction suspects,
volcanic rocks from the Siberian Traps, one of the largest volcanic outpourings on Earth.
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