[meteorite-list] Another Meteor Impact Coincides with Large-scale Volcanic Eruptions

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 26 Feb 2009 16:07:14 -0800 (PST)
Message-ID: <200902270007.QAA25572_at_zagami.jpl.nasa.gov>

http://planetearth.nerc.ac.uk/news/story.aspx?id=332

Another meteor impact coincides with large-scale volcanic eruptions

PlanetEarth oinline
23 February 2009

Scientists have long debated the cause of the dinosaurs' extinction
about 65 million years ago.

The remnants of a large volcanic eruption in the Faroe Islands. These
eruptions can go on for millions of years.

Around this time a giant meteorite struck the Gulf of Mexico. But the
extinction also seems to coincide with massive and long-lasting volcanic
eruptions in India known as the Deccan Traps. So which event was
responsible? And are these phenomena linked?

New research now shows that this combination of meteorite impact and
large-scale volcanic activity - known as flood basalt eruptions - is not
unique.

An international team of researchers looked at a 30-million-year-old
meteorite crater in Belarus called Logoisk. They found that this too
coincided with volcanic eruptions further south which covered Yemen and
Ethiopia with basalt rock.

These events are similar to those that occurred 65 million years ago,
but on a much smaller scale. The scientists suggest such coincidences
maybe more common than previously thought.

Dr Sarah Sherlock from the Open University and lead author of the paper,
says, 'If you have a flood basalt then people wonder if there's also an
impact.'

'There will be, almost certainly,' she added.

According to the paper, a meteorite will strike the Earth and leave a
crater the size of Logoisk on average once every 1.5 million years.
Flood volcanic eruptions occur over several million years, so a
Logoisk-sized crater is likely to occur during each of the 16 identified
periods of flood volcanism on Earth in the last 360 million years.

However, researchers do not think there is a causal link between flood
volcanism and meteorite impact.

'There is simply no geological evidence to link the two,' says Sherlock.

To determine the precise age of the Logoisk crater the researchers used
argon dating. 'Argon dating is very versatile.' said Sherlock. 'It's the
only technique that can be used to date both [impacts and flood
volcanism].'

Samples of material from the crater were gradually heated using an
infrared laser, causing the release of argon gas. The ratio of two
isotopes of argon released in the gas gives an accurate indication of
the age of the sample. Using this technique, the researchers showed that
the two events occurred simultaneously.

One question raised by the results was why the meteorite impact and
flood volcanism 65 million years ago wiped out much of life on Earth,
including the dinosaurs, but the similar events 30 million years ago did
not. According to Sherlock, it was down to the size of the events.

'These coincidences in Earth's history are not as rare as people think,
but in order to actually do significant damage to the environment they
have to be really, really big.' Sherlock added.

Together, the 65-million-year-old Chicxulub crater in the Gulf of Mexico
and volcanic eruptions that produced the Deccan Traps eruption 65
million years ago released 8000 gigatonnes (Gt) of sulfur dioxide,
causing global environmental damage. By comparison the Logoisk and
Afro-Arabian events released only 30Gt - insufficient to cause change on
a global scale.

The research is published in the Journal of the Geological Society, London.
Received on Thu 26 Feb 2009 07:07:14 PM PST