[meteorite-list] 1.5 Billion-Year-Old Crater Found In Finland

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:05 2004
Message-ID: <200401221701.JAA15125_at_zagami.jpl.nasa.gov>

http://www.hindustantimes.com/news/181_543619,00050003.htm

1.5 billion-year-old meteorite crater found in Finland
Agence France-Presse
Helsinki, Finland
January 22, 2004

A crater from a meteorite that collided with earth some 1.5 billion years
ago has been discovered in Finland by two amateur geologists, Finnish
scientists said on Thursday.

"The discovery is nine kilometres in diameter, but the original crater
must have been much larger, because only the floor is left, since the
rest of the crater bowl has eroded away," said Lauri Pesonen, a professor
of geophysics at Helsinki University who verified the find.

According to calculations, the crater must have been between 20 and 25
kilometres wide following the impact, he added.

Two local amateur scientists, Satu Hietala and Jarmo Moilanen, came across
the crater last fall when they found shatter cones in stones in the area.

Shatter cones, which are typical feature found in stones in meteorite
craters, are formed in the rock when the energy from the impact passes
through it.

Since the surrounding rock formation is about 1.8 billion years old,
Pesonen said the meteorite was likely to have collided with the earth
later than that, probably around 1.5 billion years ago.

The crater, partly covered by a lake, is located some 175 kilometres
north of Helsinki.

So far, 11 meteorite impacts have been found in Finland, and some 180
worldwide, Pesonen said.

----------------------------------------------------------------------


http://www.helsinki-hs.net/news.asp?id=20040122IE6

Large crater caused by meteorite found in Finland
Helsingin Sanomat (Finland)
January 22, 2004

A large crater caused by a meteorite has been found north of the community
of Mänttä. The discovery of the crater - about ten kilometres in
diameter - was reported on Wednesday in the latest issue of the Finnish
astronomy journal Tähdet ja avaruus ("Stars and Space"), which is
published by the astronomical society Ursa. The magazine has a reputation
for meticulous accuracy.

The crater is located just north of Mänttää in the Keurusselkä
area, and it could be as much as a billion years old. It is the first
landmark of its kind in Finland to be found by amateurs.

The collision fragments found in the area have been confirmed as remnants
of a meteorite. Experts confirming the discovery have included a geologist
and geophysicist from the University of Helsinki.

Teemu Öhman of the University of Oulu says that the find is the eleventh
crater caused by a meteorite to be discovered in Finland, and it could be
the largest.

The crater was originally much larger than it is now, with fairly high edges.
These have been worn down by intervening ice ages. Now only the bottom of
the crater is left, in addition to cone-shaped pieces of rock from the impact.

The cone-shaped rocks can be found in the Keurusselkä area, with the narrow
end pointing toward the centre of the impact.

On a global scale the newly-discovered Keurusselkä crater is not among the
largest. For instance, a meteorite which hit the Yucatan peninsula, and which
is believed to have caused the mass extinction of the dinosaurs about 65 million
years ago, left behind a crater with a diameter of about 180 kilometres.
Received on Thu 22 Jan 2004 12:01:18 PM PST