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CANADA : THE EARTH'S OLDEST "ROCKSTAR" FOUND

 
 
Reply Sat 27 Sep, 2008 12:42 pm
the earth's oldest rock has been found on the shores of hudson bay !

http://www.theglobeandmail.com/servlet/story/RTGAM.20080925.woldrocks0925/BNStory/Science/home

Quote:
September 25, 2008 at 2:01 PM EDT

OTTAWA " Canadian researchers have discovered the oldest rocks in the world.

The remnants of the Earth's early crust are 4.28 billion years old and were found in a belt of ancient bedrock in northern Quebec, along the eastern shore of Hudson Bay.

They have been around since roughly 300 million years since the planet was formed 4.6 billion years ago, says Jonathan O'Neil, a doctoral candidate at McGill and the lead author of a paper to be published in Friday's edition of the journal Science.


http://images.theglobeandmail.com/archives/RTGAM/images/20080925/woldrocks0925/rock2500big.jpg
 
farmerman
 
  3  
Reply Sat 27 Sep, 2008 01:15 pm
@hamburger,
You can see at least five events of emplacement, "Mixing in hot water" further metamorphism, and erosion, sedimentation, followed by more metamorphism. Very cool hbg. Id almost wish I could make a field trip to the site (if it becomes disclosed in the articles that will surely be forthcoming). The samples and "thin sections" of this very outcrop (if all the initial data are verified) will be a "type section" for the Canadian SHield and Shield deposits worldwide. Whoever owns the propert can expect to do a fortune in petrographic specimens alone. (Not to mention calibration samples for geochron courses and working geochronology labs)
The pink stuff would be some of the oldest (nay THE oldest, feldspars known, and the dark "pyroxenes" will contain zircons that can be used to determine the baseline for plotting the base of the Uranium/Thorium decay curves.

Lotta use for these rocks.

Dont tell gungasnake.
JTT
 
  2  
Reply Sat 27 Sep, 2008 01:21 pm
@farmerman,
Quote:
They have been around since roughly 300 million years since the planet was formed 4.6 billion years ago,


Farmerman or someone with knowledge in this area.

Why aren't there lots of these rocks around? Was the planet formed as a "small" version with layers added on later?
ehBeth
 
  1  
Reply Sat 27 Sep, 2008 01:22 pm
@hamburger,
What a great find!
0 Replies
 
hamburger
 
  2  
Reply Sat 27 Sep, 2008 01:32 pm
@farmerman,
glad you found the article of interest , farmerman !

by googling "canada+earth oldest rock" you can find quite a bit of information on the subject - including from NSF .
as you know , the area is kind of remote but i'd think that quite a few scientist/geoligists will be heading up there .
there should probably plenty of "rock" for any collector .
the canadian government used to sell "canadian rock collections" (about 20 different rocks in a small display case) for TWO DOLLARS (!) up until about 1985 .
a friend visiting from germany in the 80's was quite thrilled to be able to take one of those collections home with him .
hbg

http://www.cbc.ca/gfx/images/news/photos/2008/09/25/old-rocks-oneil1HR.jpg

The Nuvvuagittuq belt region along the coast of Hudson's Bay in Northern Quebec is the home of ancient rocks that may be as old as 4.28 billion years, according to a team of Canadian and U.S. researchers. (Science/AAAS)
littlek
 
  2  
Reply Sat 27 Sep, 2008 01:43 pm
@JTT,
The crust is in a constant state of recycling. Some bits are subducted under the continents, some are eroded into streams and rivers or the wind. Some eroded material makes it to large bodies of water where the particles fall gently to form layers on the floor of the waterbody to later become new rock. So rocks are decomposed, melted, twisted spewed forth, etc. Very few bits of the earth are as old as this (well, apparently none are), because this bit of land missed out on all the fun.
CalamityJane
 
  2  
Reply Sat 27 Sep, 2008 01:47 pm
Oh! I thought you're talking about Keith Richards here...
hamburger
 
  1  
Reply Sat 27 Sep, 2008 02:09 pm
@CalamityJane,
cj wrote :

Quote:
Oh! I thought you're talking about Keith Richards here...


i figured that if i just labelled it "old rock found in canada" , nobody would pay any attention .
it shows that a bit of deceptivve advertising can do wonders <GRIN>
hbg
0 Replies
 
farmerman
 
  2  
Reply Sat 27 Sep, 2008 03:30 pm
little k covered it quite well. Shields are the remnants of ancient stable "cratons" or cores of a large landmass. Its as if Kansas were saved by being in the center of a stable landmass and was never part of a leading or trailing edge of a continental mass, a shallow sea, or and interiror glaciated plain. (Theres evidence that the Canadian shield was covered by archeozoic glaciers though.

Hbg, samples, used for calibration and dating purposes, need to be collected in special means so they dont get messed up by newer rock masses or even dirt. Usually a sample, large enough, is cut and deep sampled and zircons are collected from deep within the unit.

We are getting dangerously close to the ragged edges of reliability for radioisotope dating using these rocks So the remetamorphosed units (those that looked like swirls in marble cake) need to be carefully disregarded and calibrated against other earth tectonic events..

Ill wait till it comes up in an AGU publication, Science and NAture are really the USA TODAY of Science.
Mame
 
  1  
Reply Sat 27 Sep, 2008 03:35 pm
@farmerman,
Let's hope Nature thinks it's of wide enough interest to publish. I'd love to read about it, too.
0 Replies
 
rosborne979
 
  2  
Reply Sat 27 Sep, 2008 04:06 pm
@hamburger,
Quote:
the earth's oldest rock has been found on the shores of hudson bay !

Canada has some nice geological treasures. They've also got the Burgess Shale.

It's amazing to think what the Earth was like back when these rocks were young.

JTT
 
  2  
Reply Sat 27 Sep, 2008 06:39 pm
@littlek,
Thanks for the explanation, LittleK, but I'm still missing something. Is it that these "rocks" are in their original state, that they haven't been degraded by erosion?
littlek
 
  1  
Reply Sat 27 Sep, 2008 06:51 pm
@JTT,
Apparently they haven't been entirely degraded yet. Maybe there was newer rock atop them for some time, or maybe the rock was mostly covered by ice or soil until recent history.
0 Replies
 
littlek
 
  1  
Reply Sat 27 Sep, 2008 06:51 pm
@rosborne979,
The Burgess Shale really makes you think about it!
0 Replies
 
JTT
 
  3  
Reply Sat 27 Sep, 2008 07:25 pm
@hamburger,
Quote:
the canadian government used to sell "canadian rock collections" (about 20 different rocks in a small display case) for TWO DOLLARS (!) up until about 1985 .


They had to stop because Canada was at risk of being reduced to the third largest nation on Earth.

Sorry LittleK, but I still don't get it. Maybe it's something about the process used to determine the age of the material?

Isn't all the inorganic material on Earth the same age? Isn't the magma that "makes new rock" still of the original material that formed the planet, hence the same age? Isn't a grain of sand from this rock the same age as the rock?

farmerman
 
  1  
Reply Sat 27 Sep, 2008 07:27 pm
The rock IS being wroded. Its apparent that the hammer is lying atop an erosion surface and who knows how much had been abradd before the outcrop ws found. There will have to be follwo up field work to see how the rock unit lies within the surrounding coun try-side.

I smile at Burgess shale references as if they are unique. Weve created a term for such units as the Burgess shale, and other units that lie in a circum polar series of arcs, its, LAGERSTATTEN (umlaut on the second "A"). These types of formations are unique, resulting in very fine sediments that preserved critter fossils inextreme detail. The Burgess shale , to me is the unknowing discovery of an exploration tool to help us map the resources of the circum-Arctic basinand the Lomonostov Ridge. When a bunch of independent paleos began compiling lagerstate fossil groups in areas of NE Asia, Greenland, NW territories, and in Chengjiaan China, it becamse mildly of interest to another bunch of prospectors to put it togethr that these areas were once part of apre cambrian supercontinental mass in the late PC. As Plate tectonics became better proven, these similar fossil beds were "lumped" together and paleos began ( by using the techn ique of predictive falsifiability) proving the extent of the radius arc of seafloor spreading that is parallel to the Lomonostov. (The fossils helped determine the mineral provinces of the Arctic basin)
Thus, a few mineral finds (including oil and other resources) are being put together like a common jigsaw puzzle and the resources of the Arctic have begun to be opened> Thanks , in part to a story of a single Canadian geologist whose discovery of a bunch of well preserved fossils ultimately led to the discovery .

0 Replies
 
littlek
 
  1  
Reply Sat 27 Sep, 2008 08:13 pm
@JTT,
All of the molecules were here at the same time. As the earth clumped together and became a compact unit, rock formed. Most of the early rocks were recycled in one way or another. For some reason other rocks weren't.

Consider Australia (erosion). Australia is largely flat, there are few mountains or canyons. This is what an old piece of earth looks like. Think of Ayer's rock in Oz (Uluru). That chunk of rock was harder to erode than the rock that was around it. All of that area had a surface of the same altitude at one time.

Consider the Himalayas (transforming). They are still being built, the top of the mountains contain fossils of sea life because it was once under the Indian Ocean. As that ocean floor collided with the Asian continent, the two pushed up like a throw rug that a dog just skidded into.

Consider the Ring of Fire (sublimation). The continents are drifting along atop tectonic plates that are moving. Some collide as in the Himalayan scenario and some don't. Near Japan, the ocean floor is pushing against Asia. But, this time, the ocean floor is going under the the continent. It goes under and melts (recycling), sometimes to be released during volcanic activity (new rock formation).

Sometimes rocks just sink under the weight of rocks above them to a point in the earth where they become elastic because of heat and pressure (transformed rock). Here they can twist and corrugate like taffy only to be exposed to light again after an earth quake.

Ah, earth quakes! When the tectonic plates I was talking about don't ram into each other, sometimes they just sort of slide past one another. The earthquakes in california are due to this type of movement, the West side of the fault line may go North while the East side may go South. Sometimes an slide can go up and down - the West side of the fault may rise while the East side drops down. The risen side will be exposing older rock (it's deeper in the earth).
0 Replies
 
rosborne979
 
  1  
Reply Sat 27 Sep, 2008 08:47 pm
@JTT,
Quote:
Isn't all the inorganic material on Earth the same age? Isn't the magma that "makes new rock" still of the original material that formed the planet, hence the same age?

The atoms of the rock are much older than the rock (and much older than the Earth). When they talk about the "age" of this rock, they are talking about when it became a rock (solidified).

When we talk about the "age" of atoms we're talking about when the current configuration of protons occurred. Atoms with more than 3 protons were formed inside of stars. Atoms with more than 26 protons (Iron) were formed by supernovae.



0 Replies
 
farmerman
 
  2  
Reply Sun 28 Sep, 2008 09:33 am
The amount of physical material that makes up the earth is pretty much constant since early earth. However the stuff is constantly being recycled by earth processes. (KInda like taking a barrel of paraffin and heating it up each year and then jamming todsys newspaper into the hot paraffin. So to measure the ages of many of the material deposist we use radioisotopes with very long half lives as the "newspapers"( we look at Isotopes like Lutetium176, and Hafnium176,177, Uranium 238 234 and 235,Thorium232,Rubidium87, Potassium40 and lead 207,210). There are several others but these above are those isotopes that will substitute within the crystal structures of minerals being formed in a "melt"
So the rocks of the CAnadian shield are showing us that it was about 4.2 By since theyve been remelted (the remelting "resets" the atomic clocks). Thats the reason that sampling and multiple analyses are practised carefully, as well as sample calibration, isotope ratio determinations etc.

The newest technique for analyases is called SHRIMP (a type of MS analysis)

So we can look at each zircon crystal and subsample the uranium isotopes and daughter products from the crystal lattice to determine the last event of metamorphism that resulted in a melting of the rock (This is called "natexis")
WHat gets me is that, if the rock , as it does, indicate tht its a metamorphic rock, then its even older than the reported last anatectic event.
Waaay too cool for my little mind.
rosborne979
 
  2  
Reply Sun 28 Sep, 2008 10:20 am
@farmerman,
Quote:
So the rocks of the CAnadian shield are showing us that it was about 4.2 By since theyve been remelted (the remelting "resets" the atomic clocks).

Hi FM, why does remelting "reset" the atomic clocks? I'm not sure I understand the process involved.

Thanks,

 

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