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Fraser
2005-Aug-05, 04:09 PM
SUMMARY: At least three massive asteroids smashed into the Earth more than 3.2 billion years ago, and caused such destruction, they dramatically changed the structure and composition of the Earth's surface. This is according to new research from scientists at the Australian National University. The team uncovered evidence of major earthquakes, faulting, and volcanic eruptions that were so violent they dramatically changed the way the Earth's surface was forming. This happened during a period that the Moon also suffered heavy bombardment.

View full article (http://www.universetoday.com/am/publish/earth_surface_transformed_by_asteroids.html)

What do you think about this story? Post your comments below.

lswinford
2005-Aug-05, 08:31 PM
That was about the time the Canadian Shield was formed. Interesting.

GOURDHEAD
2005-Aug-06, 12:09 AM
Do the authors of the paper assume that several asteroids hit within hours of each other or over a much longer (or shorter) time interval?

cran
2005-Aug-06, 12:02 PM
Do the authors of the paper assume that several asteroids hit within hours of each other or over a much longer (or shorter) time interval?
In the geologic record, gourdhead, it would register as a single event - estimates of duration of the impacts would be based on the number and spread of impact sites; the only one mentioned is Barberton - suggests an impact duration of seconds-minutes.
Other impact events citing multiple bolides do so because of contemporaneous impact sites across part of the globe - duration estimates in hours - think Shoemaker-Levy 9 striking Jupiter.
If the event is thought to be part of a large, even cyclic, swarm then duration estimates may extend into days, or as semi-annual or annual episodes...hard to justify without some form of corroboration, but in the rock record it remains a single event.
The consequences (tectonism, vulcanism, climate indicators), on the other hand, may show evidence of durations spanning millenia.
Hope that helps.

That was about the time the Canadian Shield was formed. Interesting.
Yes, isn't it? Apart from the Pilbara, and Barberton, there should be some evidence in the Greenland strata...

GOURDHEAD
2005-Aug-06, 01:12 PM
I am amazed that they were able to conclude so much from so little data and how they are certain that some other history does not pertain.

cran
2005-Aug-06, 03:00 PM
Originally posted by GOURDHEAD@Aug 6 2005, 09:12 PM
I am amazed that they were able to conclude so much from so litle data and how they are certain that some other history does not pertain.
Ah, I hope we are not confusing a (necessarily) truncated interpretation of a (necessarily truncated) press release, with a full report of findings - which, itself, is a synthesis of masses of background research and field and lab studies...

think of journalism (especially science journalism) as a form of 'Chinese whispers' where each stage must also compress the information being passed on... :unsure:

Linking widely separated bits of data into a coherent whole is part of the process...thus evidence of catastrophic geological activity all being dated to the same age (and I note that inlcudes Luna data in this case) really does lead one to think of a multiple bolide or global event.

I'm not sure which history you feel is considered impertinent...doesn't pertain...

Also keep in mind, and this goes back to the earlier posts- in geology, one million years is a very short period of time; or if you prefer, the older the evidence - the greater the margin of error in precise date

GOURDHEAD
2005-Aug-07, 10:58 AM
I'm not sure which history you feel is considered impertinent...doesn't pertain... I was attempting to challenge their discarding (not considering) other plausibilities. It is easy to believe that plausibles outnumber actuals.

cran
2005-Aug-07, 11:13 AM
okay... :unsure:

Eric Vaxxine
2005-Aug-08, 02:28 PM
Barberton .... I grew up near Barberton (in Nelspruit)
Never knew it had old rocks until recently. Then I learned of the Vredefort impact ....I lived in that region for 7 years too.

cran
2005-Aug-08, 11:46 PM
Originally posted by Eric Vaxxine@Aug 8 2005, 10:28 PM
Barberton .... I grew up near Barberton (in Nelspruit)
Never knew it had old rocks until recently. Then I learned of the Vredefort impact ....I lived in that region for 7 years too.
Now, Eric Vaxxine, that&#39;s not fair&#33; <_<
You can&#39;t just dangle the bait like that...did you visit the impact site(s)?
What does the area look like?
Were you inspired to research its origin?
Did you get any samples of impact-affected rocks?
Did you get any pictures?
Huh? Didja? Huh? :ph34r:

Eric Vaxxine
2005-Aug-09, 11:08 AM
Y&#39;know, they never told us at school, in Geography, that we were living in such an area. I LOVED geography as well.
The Barberton/Nelspruit area is amazing, hilly, typical African bush in whats called the Lowveld, as opposed to the escarpment which is the Highveld (Johannesburg etc).

The highveld is all pretty flat, but riddled with gold. The Vredefort impact was, quite a long time ago and the area is not very inspiring but I wish I had visited the meteor impact in Pretoria.

http://www.hartrao.ac.za/other/tswaing/tswaing.html

I have been back twice in four years (friends, my old school etc) and it
is one of my missions next to go to Barberton and collect some of the solidified mud pool rocks from that age. Wanna come?
There is a great bar called the Green Venus in Kaapsehoop, not far from Barberton and Nelspruit.

cran
2005-Aug-10, 12:02 AM
Wanna come? Would, if&#39;n I could, Eric... :)
Unfortunately, I&#39;ve still got at least two years to wait for some operations which might let me go on long journeys, and backpacking, climbing, carting rocks, etc... :(
But, I&#39;ll be with you in spirit, and waiting for the results&#33; :D

Eric Vaxxine
2005-Aug-10, 08:01 AM
Get well soon Cran.
Imagine million year old mud pool rock sitting on the mantlepiece (no pun intended)...beats the collection of old coins.

cran
2005-Aug-10, 08:25 AM
thank you, Eric :)

I&#39;ve got a few million (and billion) year old rocks and fossils on bookcases and other shelves :)...even more at university :D ...couldn&#39;t tell you a thing about &#39;em :blink: .... neither of them compete with our palaeontogy professor (Ken McNamara)&#39;s collection&#33; (he&#39;s also one of the directors/curators of the mineral and fossil section of the state museum :D :D and another geology professor (Simon Wilde) who discovered the oldest known terrestrial zircon (with evidence of relatively cool formation regime) ...but always happy to see more of &#39;em... B)

Ola D.
2005-Aug-10, 10:15 AM
Originally posted by GOURDHEAD@Aug 6 2005, 12:09 AM
Do the authors of the paper assume that several asteroids hit within hours of each other or over a much longer (or shorter) time interval?
As a Community Support Member, I&#39;ve contacted researcher Dr Andrew Glikson regarding your question. And he answered:


Four asteroid impact ejecta units have been identified to date in the
Barberton greenstone belt, eastern Transvaal, including:

A.* 3470.42.3 Ma (million years) (BGB-S1A & BGB-S1B upper Hooggenoeg
Formation, Onverwacht Group, Kaapvaal Craton)

B.* 32583 Ma* (BGB-S2 at the base of the Mapepe Formation, Fig Tree Group,
Kaapvaal Craton)

C.* 32434 Ma* ( TWO ASTEROIDS - BGB-S3 and BGB-4 lower part of Mapepe
Fm* (Fig Tree Group, BGB)

The second asteroid ( B ) has preceded the following asteroids by at
least 8 million years. The 2 last asteroids hit the Earth almost
simultaneously.

Please do not hesitate to request further information.

Regards
Andrew Glikson

cran
2005-Aug-10, 11:03 AM
Wow&#33; thanks for that, Ola D. :) and Andrew, thank you&#33; :D

That puts things in a rather different light...
...interesting temporal spread between impact events...~210MA between A and B...and then ~14(+/-6)MA between B and Cs...hmmm <_<

...does anyone think that a particular part of the galaxy might have been holding a grudge against us? :(