However it came about,
the Permian extinction was toxic to marine life and we are not quite sure how
this became a problem while somewhat sparring life on land. Perhaps the simplest explanation is
best. The sustained volcanism poisoned
both land and sea but the land had the mechanism of transferring such poison
directly to the seas. The poisoning rate
was higher that the sea’s ability to absorb that poison.
Suphur is the best
prospect for this. The extent of the
traps suggest that the process was continuous for a very long time. Thus acidity may have built up in the sea to
a point a simple eruption burst took everything all over the top.
That life must have thrived
throughout this in natural refugia at least conforms to this model. In fact it may have done rather well although
stressing the population to individual extinctions.
Canada’s Arctic islands
yield new clues in ancient mass extinction
BY
RANDY BOSWELL, POSTMEDIA NEWS JULY 14, 2013 1:00 PM
Canadian
scientists probing two sites in the High Arctic have found fresh evidence
pointing to a fiery Siberian suspect in the greatest mass extinction of all
time — a planet-wide cataclysm that wiped out more than 90 per cent of the
Earth’s species about 250 million years ago.
The
so-called “Great Dying” at the end of the Permian geological era killed off a
larger proportion of species than any of the 25 other mass extinctions
scientists have identified from sudden and widespread gaps in the fossil record
at certain layers of rock corresponding to specific periods of time.
The
precise cause of the biological catastrophe 252 million years ago has been
debated by scientists for decades. But nothing else in Earth history compares
to the Late Permian disaster, which eclipsed 95 per cent of all marine life and
about 70 per cent of species on land.
Some
have argued that a massive meteorite strike — like the one widely presumed to
have triggered the end of the dinosaur age 65 million years ago — must have
been to blame. Others point to extreme climate change linked to ocean
acidification, oxygen depletion, mercury poisoning or other species-snuffing
effects as the main driver of the extinctions.
And
without discounting the other forces as potential contributors to the Great
Dying, a growing number of scientists — including several groups of Canadian
researchers who are among the world’s leading investigators of the die-off —
have fingered a prolonged series of enormous volcanic eruptions in northern
Asia known as the “Siberian Traps” as the main culprit in the Permian
extinction.
The
latest clues in the prehistoric puzzle, which reinforce the volcanism theory,
come from Ellesmere Island and nearby Axel Heiberg Island in the Canadian
Arctic,
where five researchers from the University of Calgary and the Geological Survey
of Canada have found evidence undercutting the idea that oxygen depletion
occurred uniformly throughout the world’s oceans and may have been the prime
agent of death in the Great Dying.
At
Axel Heiberg’s Lake Buchanan and Ellesmere’s West Blind Fiord, geological sites
offering two of the best-known windows on the Permian extinction, the Canadian
team tested rock samples for the element molybdenum — a “powerful tracer” used
in reconstructing the oxygen levels of ancient marine environments — to better
understand what was happening in waters off the coast of the supercontinent
Pangea 252 million years ago.
At
that time, the now-exposed Lake Buchanan and West Blind Fiord sites were lying
at the bottom of the primordial ocean close to the equator.
The
researchers, led by U of C geoscientist Bernadette Proemse, determined that the
Lake Buchanan site — which preserves a deep-water seabed environment from the
time of the Great Dying — showed clear signs of “anoxia” or extreme oxygen
deprivation.
But
the shallower Permian seafloor found at West Blind Fiord, which preserves a
stretch of Pangea’s extinction-era continental shelf, showed a fairly
well-oxygenated marine environment even as the Great Dying was unfolding.
In
short, the findings confirm oxygen starvation as a significant factor in some
phases or sites of the global crisis, but rule it out as the underlying cause
of the planet-spanning extinctions, the researchers conclude.
Their
study was published in the latest issue of the journal Geology.
“It is clear that
anoxia cannot be the direct cause of the extinction,” the scientists argue, pointing to
the oxygenated seawater available at the Ellesmere Island site. “Rather than
the direct cause of global extinction, anoxia may be more a contributing factor
along with numerous other impacts associated with Siberian Traps eruption and
other perturbations to the Earth system.”
The
impacts from the Siberian eruptions, “the largest volcanic event in Earth
history, are increasingly recognized as devastating to global ecosystems” at
the end of the Permian era, the researchers added. “Widespread anoxic
conditions are more likely a symptom of other external factors placing multiple
stresses on the global environment due to massive eruptions of the Siberian
Traps at that time.”
Traces
of the ancient volcanic calamity itself can be seen across a wide area of
present-day Russia near the Siberian city of Norilsk.
The
researchers involved in the new Geology study have published previous papers on
the Permian extinction. Co-authors Stephen Grasby, a GSC geologist who also
teaches at the University of Calgary, and fellow U of C scientist Benoit
Beauchamp collaborated on a 2011 research project that pointed to layers of
coal ash found at Lake Buchanan as “smoking gun” proof that the fiery Siberian
Traps were wreaking havoc on the global climate and suffocating life almost everywhere
around the world.
In
2008, another team of Canadian scientists announced the discovery of a thin
band of rock running through B.C., Alberta and Arctic Canada that appears to
have served as a rare coastal refuge for life during the Great Dying.
The
refuge was identified by its diverse and abundant deposits of fossils, proof
that a “thriving” array of clams, worms and other seabed species endured in at
least one narrow strip of ancient Canada at time when nearly all of the world’s
other terrestrial and marine ecosystems had become poisonous to life.
rboswell@postmedia.com
No comments:
Post a Comment