Precambrian impact -- AMIGA Astronomy

[ Show ]

Support VoyForums

[ Shrink ]

VoyForums Announcement: Programming and providing support for this service has been a labor of love since 1997. We are one of the few services online who values our users' privacy, and have never sold your information. We have even fought hard to defend your privacy in legal cases; however, we've done it with almost no financial support -- paying out of pocket to continue providing the service. Due to the issues imposed on us by advertisers, we also stopped hosting most ads on the forums many years ago. We hope you appreciate our efforts.

Show your support by donating any amount. (Note: We are still technically a for-profit company, so your contribution is not tax-deductible.) PayPal Acct: Feedback:

Donate to VoyForums (PayPal):

[ Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: [1], 2 ]

Subject: Precambrian impact

Author:
Blobrana

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Date Posted: 20:05:30 12/03/04 Fri

The first convincing evidence of a massive meteorite impact that occurred 2.63 billion years ago has been found in northwestern
Australia's Pilbara region.

Dr Birger Rasmussen of the University of Western Australia and Associate Professor Christian Koeberl of the University of Vienna report their discovery in the latest issue of the journal Geology.

Some scientists have long suspected that certain features of the Jeerinan Formation in the area known as the Pilbara Craton were signs
Of a large meteor that hit the Earth in the Precambrian period.

However, Rasmuassen and Koeberl said the only evidence for this had been small splatters of melted rock called spherules, between 3.4 and 2.6 billion years old.

Until now, the area had lacked the indisputable hallmarks of a
Meteorite impact: high iridium levels and shocked quartz.

Earth's own iridium is locked away in the planet's core but meteorites are full of the metal and thus a spike in iridium levels is used to detect debris from meteorite impacts.

Quartz crystals in rocks display a particular texture known as shocked quartz, which can only be formed by the impact of a bomb or a meteorite.

Until now, such evidence had not been found in the Pilbara rocks.
However, a new search discovered shocked quartz in layers of the rock also containing melt spherules and high iridium levels.

This provides "compelling evidence" for an extraterrestrial impact, which was likely to be on land.

But where's the crater?

While this was among the largest yet documented impacts in
The Precambrian rock record, no one knows exactly where the crater is.

By studying comparative rocks in South Africa, it is shown that the meteorite would have caused a blanket of material to be thrown out across 32,000 square kilometres covering South Africa and Australia, which were joined at the time.

This research as �another notch on the record of confirmed impacts that have happened to Earth. It's a nice piece of detective work."

The only life forms present at the time of the impact were single-celled photosynthetic algae. However, not enough palaeontological evidence exists to know what effect the meteorite impact would have had on these.

But the impact was not "as big a deal" as the meteorite that hit at the end of the Cretaceous period that has been implicated in the extinction of the dinosaurs.

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Replies:

Subject	Author	Date
Re: Precambrian impact	Blobrana	23:38:59 12/13/04 Mon
Re: Precambrian impact -- Blobrana, 08:50:30 04/15/05 Fri