[meteorite-list] First Ever Evidence Of A Comet Striking Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 8 Oct 2013 10:29:07 -0700 (PDT)
Message-ID: <201310081729.r98HT7Pl018240_at_zagami.jpl.nasa.gov>

http://www.uj.ac.za/EN/Newsroom/News/Pages/First-ever-evidence-of-a-comet-striking-earth.aspx

First ever evidence of a comet striking earth
University of Johannesburg
October 8, 2013

The first ever evidence of a comet entering Earth's atmosphere and exploding,
raining down a shock wave of fire which obliterated every life form in
its path, has been discovered by a team of South African scientists and
international collaborators, and will be presented at a public lecture
on Thursday.

The discovery has not only provided the first definitive proof of a comet
striking Earth, millions of years ago, but it could also help us to unlock,
in the future, the secrets of the formation of our solar system.
 
"Comets always visit our skies - they're these dirty snowballs of ice
mixed with dust - but never before in history has material from a comet
ever been found on Earth," says Professor David Block of Wits University.
 
The comet entered Earth's atmosphere above Egypt about 28 million years
ago. As it entered the atmosphere, it exploded, heating up the sand beneath
it to a temperature of about 2 000 degrees Celsius, and resulting in the
formation of a huge amount of yellow silica glass which lies scattered
over a 6 000 square kilometer area in the Sahara. A magnificent specimen
of the glass, polished by ancient jewellers, is found in Tutankhamun's
brooch with its striking yellow-brown scarab.

The research, which will be published in Earth and Planetary Science Letters,
was conducted by a collaboration of geoscientists, physicists and astronomers
including Block, lead author Professor Jan Kramers of the University of
Johannesburg, Dr Marco Andreoli of the South African Nuclear Energy Corporation,
and Chris Harris of the University of Cape Town.
 
At the centre of the attention of this team was a mysterious black pebble
found years earlier by an Egyptian geologist in the area of the silica
glass. After conducting highly sophisticated chemical analyses on this
pebble, the authors came to the inescapable conclusion that it represented
the very first known hand specimen of a comet nucleus, rather than simply
an unusual type of meteorite.
 
Kramers describes this as a moment of career defining elation. "It's a
typical scientific euphoria when you eliminate all other options and come
to the realisation of what it must be," he said.
 
The impact of the explosion also produced microscopic diamonds. "Diamonds
are produced from carbon bearing material. Normally they form deep in
the earth, where the pressure is high, but you can also generate very
high pressure with shock. Part of the comet impacted and the shock of
the impact produced the diamonds," says Kramers.
 
The team have named the diamond-bearing pebble "Hypatia" in honour of
the first well known female mathematician, astronomer and philosopher,
Hypatia of Alexandria.
 
Comet material is very elusive. Comet fragments have not been found on
Earth before except as microscopic sized dust particles in the upper atmosphere
and some carbon-rich dust in the Antarctic ice. Space agencies have spent
billions to secure the smallest amounts of pristine comet matter.
 
"NASA and ESA (European Space Agency) spend billions of dollars collecting
a few micrograms of comet material and bringing it back to Earth, and
now we've got a radical new approach of studying this material, without
spending billions of dollars collecting it," says Kramers.
 
The study of Hypatia has grown into an international collaborative research
programme, coordinated by Andreoli, which involves a growing number of
scientists drawn from a variety of disciplines. Dr Mario di Martino of
Turin's Astrophysical Observatory has led several expeditions to the desert
glass area.
 
"Comets contain the very secrets to unlocking the formation of our solar
system and this discovery gives us an unprecedented opportunity to study
comet material first hand," says Block.
 
Public lecture:
 
Please join Professor Jan Kramers, Professor David Block and Dr Marco
Andreoli as they reveal their new discovery.
 
Date: Thursday, 10 October 2013
Time: 17:30 for 18:00
Venue: Auditorium 3, Wits Science Stadium, West Campus
RSVP: 011 717 1146 or kelebogile.tadi at wits.ac.za
 
Images:
High resolution images can be downloaded by left clicking on the images
available at:
http://www.wits.ac.za/newsroom/newsitems/201310/21649/news_item_21649.html
 
Online paper:
An online version of the scientific journal article can be accessed at:
http://www.sciencedirect.com/science/article/pii/S0012821X13004998
Received on Tue 08 Oct 2013 01:29:07 PM PDT