Write your abstract here. The Day the Seas Died: What Can the Greatest of All
Extinction Events Teach Us About Climate Change
?
The "Great Dying" at the end of the Permian period, some 250 million
years ago, was the most catastrophic of the five mass extinctions in
Earth’s fossil record. More than half of the families of living things
died out, and as many as 95 percent of the planet’s
marine species were
lost. At the same time, 70% of the land’s reptile,
amphibian, insect, and plant families became extinct. This mass-
extinction event may hold clues to current global
carbon-cycle changes, according to Jonathan Payne, Asst Prof.
of geological and environmental sciences at Stanford University. What caused the calamity has long been a source of scientific
controversy, due to the extreme remoteness of the event, and an
absence of geological evidence – the world’s seas retreated at the same
period, reducing the amount of sedimentary rock entering the geological
record. Recent discovery of sections from the Permo-Triassic
boundary in South China has, however,
allowed more detailed analysis to take place, leading to a conclusion that the Great Dying was probably caused by poisonous gas,
released by a massive volcanic event in Siberia, known as the Siberian Traps,
which spewed about 3 million cubic km of basalt lava over vast
swathes of the Siberian landmass. The
largest eruption in historical time, of Mt Pinatubo in Iceland in 1783,
released 12 cubic km of lava onto the island. Payne, a paleobiologist who joined the Stanford faculty in 2005,
studies the Permian-Triassic extinction and the following 4 million
years of instability in the global carbon cycle. In July issue of the Geological Society of America Bulletin,
Payne presented evidence that a massive, rapid release of carbon may
have triggered this extinction. "People point to the fossil record as a place where we can learn
about how our actions today may affect the future course of evolution,"
Payne said. "That''s certainly true: The deep geologic record provides
context for modern events. We may miss very important processes or
underestimate the magnitude of changes in the future by using only the
past couple thousand years as a baseline." Payne spent the past 5years unearthing the deep geologic
record in south China''s km-thick, limestone fossil beds at the
Great Bank of Guizhou, formed in shallow ocean waters during
the late Permian and early Triassic periods. As the ocean floor sank,
new, younger layers of limestone formed on top of deeper, older ones. Continental plate tectonics have since flipped these marine fossil
beds on their side, allowing Payne to walk back in time across the
formerly horizontal layers. Because ocean waters cover large areas for
long periods of time and somewhat protect the underlying rocks from
erosion, marine fossil beds tend to be physically larger and cover a
longer period of time with finer temporal resolution. More than 90% of all marine species disappeared from the
Great Bank of Guizhou and other end-Permian fossil formations. Douglas Erwin, curator of the Paleozoic invertebrates collection at
the Smithsonian National Museum of Natural History, has dubbed this
extinction event "The greatest biodiversity crisis in the history of life." An unusually long period of time passed before biological diversity
began to reappear. Scientists disagree on the causes of this
extinction. However, nearly all explanations cite the high levels of
greenhouse gases, including carbon dioxide, low levels of oxygen in the
oceans and high levels of toxic gases. In 1991, scientists reported that the largest known volcanic event
in the past 600 million year known as the Siberian Traps (image above), occurred at
the same time as the end-Permian ection. Magma extruded through
coal-rich regions of the Earth''s crust and blanketed a region the size
of the continental United States with basalt to a depth of up to 6
km. The eruptions that formed the Siberian Traps not only threw ash,
debris and toxic gases into the atmosphere but also heated the
coal and released vast quantities of carbon dioxide and methane into
the atmosphere. Rapid release of these greenhouse gases would have caused the oceans
first to become acidic and become supersaturated with calcium
carbonate. The researchers believe that the volcanic gases from the eruption,
which would have heated the
coal and released vast quantities of carbon dioxide and methane into
the atmosphere depleting the Earth’s protective ozone layer and
acidified
the land and sea, killed rooted vegetation. This meant that soil was no
longer retained, and eventually washed into the surrounding oceans.
Soils in the oceans would have blocked out light and soaked up
oxygen. Analysis of rock chemistry suggests that after the soil crisis
on land, the marine ecosystem succumbed to the stresses of
environmental change and oceanic life faltered, completing a global
catastrophe. Payne presents evidence that
underwater limestone beds around the world eroded at the time of the
end-Permian extinction. This finding, coupled with geochemical evidence
for changes in the relative abundances of carbon isotopes, strongly
suggests an acidic marine environment at the time of the extinction. "This end-Permian extinction is beginning to look a whole lot like
the world we live in right now," Payne said. "The good news, if there
is, is that we have not yet released as much carbon into the
atmosphere as would be hypothesized for the end-Permian extinction.
Whether or not we get there depends largely on future policy decisions
and what happens over the next couple of centuries." Today, land degradation is a
worsening global problem. Thanks to human activity, soil erosion has
caused the loss of a third of arable land over the last forty years, 35% of the Earth’s land is now soil-free.identifying the nature of
the end-Permian crisis may help us understand what is in store for
us in the years ahead. Galaxy News Reported Oct 10th, 2007.