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Oldest rocks in the U.S. in our back yard - WhiteFox

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September 19th, 2011

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05:56 am - Oldest rocks in the U.S. in our back yard
Ok, not quite in our back yard, but at least the same state.

This weekend we were watching Eureka and the episode in question metioned several times that the town didn't get Earth quakes.  Since they mentioned in was in Oragon in several episodes and because I'm a disaster freak, I knew this was wrong.  All the Pacific states are at a high risk, including Oragon and I mentioned this.  Little-J then said, well of course, no place is safe from Earth quakes.

So I told him there were places in the world where Earth quakes are all but unkown.  He asked where and I pointed out Minnesota.  The bedrock of most of MN is iron impregnated granite (they don't call it the iron range for no reason).  It's hard, it's solid, and it's deep.  As far as Earth quake danger, we're the lowest risk in the U.S., with no recorded history of quakes over a 5 magnitude and only 2 recorded over a magntude 4 (5 could crack the plaster in a wall, 4 feels like a large heavy truck is driving by your house).  

The conversation made me decide to do some research on the subject, and one of the things I found out is that this reagoin is a lot more seismically stable than even I know.  It turns out that the geology of MN is some of the oldest in the world dating back 3.8 billion years (plus or minus a hundred million years).  The rock outcroppings at Granite Falls MN are the oldest exposed rocks in the U.S.

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[User Picture]
Date:September 26th, 2011 01:14 am (UTC)
Up until recently (25 years or so) we actual had the worlds oldest known rock

Edited at 2011-09-26 01:15 am (UTC)

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