[meteorite-list] Brimstone Pickled Permian

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:49:01 2004
Message-ID: <200109181734.KAA05770_at_zagami.jpl.nasa.gov>

http://www.nature.com/nsu/010920/010920-6.html

Brimstone pickled Permian

Two hundred million years before the dinosaurs' demise another meteorite
impact may have devastated life on Earth.

PHILIP BALL
Nature Science Update
September 18, 2001

Two hundred and fifty million years ago, life on Earth nearly ceased. A
giant meteorite, six times larger than the one that did away with the
dinosaurs almost two hundred million years later, may have caused the
massive extinction at the end of the Permian period, researchers now
suggest.

Kunio Kaiho of Tohoku University, Japan, and his colleagues have found
evidence in southern China that a massive impact converted huge amounts of
solid sulphur into sulphur-rich gases[1].

The released sulphur could have consumed 20-40 per cent of the atmosphere's
oxygen, and generated enough acid rain to raise the acidity of the ocean's
surface waters temporarily to that of lemon juice. Ocean life would have
been pickled.

The fossil record shows that 95 per cent of all species disappeared in the
mass extinction that ended the Permian period. The event was more dramatic
even than the perishing of 70 per cent of species - including the dinosaurs
- at the boundary of the Cretaceous and Tertiary periods 65 million years
ago. The Cretaceous-Tertiary extinction is generally blamed on a meteorite
impact in what is now the Gulf of Mexico.

For many years, the Permian extinction was thought to have been more
gradual, perhaps resulting from slow environmental changes. The formation of
vast plains of volcanic rock called the Siberian Traps, some researchers
suggest, released gases that either boiled or froze the Earth, through the
greenhouse effect or the reflection of sunlight from dust-like particles.

Other evidence points to the Permian extinction having been abrupt,
happening within 8,000-100,000 years - a timescale that implicates an
impacting comet or asteroid. This idea is supported by the discovery earlier
this year[2] of fullerenes, cage-like carbon molecules, in sediments from the
end of the Permian. The molecules contained atoms of rare gases such as
helium, implying that they came from a meteorite.

Now Kaiho's team has found sulphate in end-Permian limestone, marl and shale
rocks formed from shallow sea-floor sediments. The rocks also have a
nickel-rich layer, which could have been carried by an impacting meteorite.
Moreover, in the nickel-rich layer, the researchers detect a sudden change
in the relative amounts of different sulphur isotopes (whose atoms have
slightly different masses).

If a giant meteorite impact vaporized a large area of sulphur-containing
rock where it struck the seabed, it would probably have ejected the lighter
of sulphur's two common natural isotopes into the air, changing the isotope
ratio of the remaining rocks.

>From the size of isotope ratio shift, Kaiho's group estimates that the
meteorite could have been up to 60 kilometres across. The
Cretaceous-Tertiary meteorite was probably less than 10 km across.

References

  1. Kaiho, K. et al. End-Permian catastrophe by a bolide impact: evidence
     of a gigantic release of sulfur from the mantle. Geology, 29, 815 -
     818, (2001).
  2. Becker, L., Poreda, R. J., Hunt, A. G., Bunch, T. E. 7 Rampino, M.
     Impact event at the Permian-Triassic boundary: evidence from
     extraterrestrial noble gases in fullerenes. Science, 291, 1530 - 1533,
     (2001).
Received on Tue 18 Sep 2001 01:34:03 PM PDT