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World's Oldest Rocks Found
Smivs writes "The BBC reports that Earth's most ancient rocks, with an age of 4.28 billion years, have been found on the shore of Hudson Bay, Canada. Writing in Science journal, a team reports finding that a sample of Nuvvuagittuq greenstone is 250 million years older than any rocks known. It may even hold evidence of activity by ancient life forms. If so, it would be the earliest evidence of life on Earth — but co-author Don Francis cautioned that this had not been established. 'The rocks contain a very special chemical signature — one that can only be found in rocks which are very, very old,' he said."
Not everyone agrees.
This was covered a few days ago on New Scientist...
http://environment.newscientist.com/article/dn14818-discovery-of-worlds-oldest-rocks-challenged-.html
I don't know about "50 years", or how deeply this counts as documentation, but there's a decent run-down here: http://en.wikipedia.org/wiki/Allegorical_interpretations_of_Genesis#Contemporary_Christian_considerations
The "money quotes" are from Pope John Paul II -
The full discourse from the pontiff is linked on Wikipedia, but it's here for your convenience: http://www.ewtn.com/library/PAPALDOC/JP2COSM.HTM
HTH.
Man who leaps off cliff jumps to conclusion.
Actually, upon reading the full discourse, the following is an even-more-money-quote: (emphasis mine)
Man who leaps off cliff jumps to conclusion.
As is stated in the New Scientist article, the technique used might actually date the protolith (the material from which this rock formed) and not the actual rock itself. From a geochronologist's stand point, this rock is actually 3.8 billion years old, based on the U-Pb zircon age given in the Science article. The age determination for the reigning oldest rocks discovered was found through U-Pb zircon work. The authors are very clear to point out that this 4.28 Ga date is not a definitely age for the rock. Gotta love the media jumping head long in front of the science.
It doesn't matter when the elements formed, we just have to know what their relative abundances were then and compare that to the current state.
The neodymium system is complicated, as are all real world measurements to some extent, so consider an idealized system. Suppose that uranium consisted of a single isotope with a half life of four billion years, and it decays to lead. Now further assume that zircons when they form contain some uranium but no lead at all, because its atoms cannot fit into the crystal lattice. If we measure the uranium and lead in a zircon and find that uranium and lead levels are equal then it must have formed four billion years ago, since that is the half life and half the uranium has decayed.
a,e,i,o,u and sometimes w and y (at be if of up cwm by)
Okay firstly, I won't be backing this up with links because I am generally too lazy this afternoon to bother, but here is what some of the story is.
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The reason that old rocks are so important is as follows:
The earth, along with all the planets and sun in our solar system was formed from a disc of dust (same as any other sort of planetary system as anyone can tell). Our earth was initially formed WITHOUT a moon. About 4.something billion years ago, our planet hard some initial surface and crust and all that. About that time, an object around the size of Mars hit the earth. This had a number of causes:
1) It penetrated the surface of the planet (Duh!!) and caused a large amount of the core of our forming planet to get whacked out into orbit.
2) This made the moon if you needed clarification.
3) The force of the blast meant that the effective entire crust of the earth was again submerged into the insides of the earth.
The last part is the most important to this article, as there are very very few "rocks" that can survive that sort of hear/pressure without being changed beyond recognition. One of these is Zircon. So far, some of the oldest rocks to date have been dug up in Western Australia and are Zircon. The belief is that these were either formed on earth prior to the impact or came on the thing that hit us (I can't remember which).
Either way, there you have a small lesson, and also likely the longest post I have written on
Moved to http://soylentnews.org/. You are invited to join us too!
Further, we have known for a while now about natural fission reactors in Africa that, while showing evidence of functioning at one time, could not have possibly ever worked given our current value of the FSC. In short: looks like radioactive decay isn't so constant.
Actually, quite the opposite. The Oklo find indicates that alpha has not changed, though it could be that other properties have also changed and exactly offset the change in alpha. It couldn't have happened today because there is to small a proportion of U-235 realtive to U-238, because the former have a shorter halflife.
You're close.
"1) It penetrated the surface of the planet (Duh!!) and caused a large amount of the core of our forming planet to get whacked out into orbit."
It's kind of the other way around. The core of the impacting body was mostly incorporated into the Earth (making it, on average, denser), and the Moon formed mostly out of the mantle/outer part of the impacting body and parts of the Earth that were blown into orbit, making it, on average, lighter, and the lunar material has a more refractory composition (i.e. more depleted of volitile material).
"3) The force of the blast meant that the effective entire crust of the earth was again submerged into the insides of the earth."
Hmmmm.... well, most of the entire surface became molten, but I wouldn't describe the process as "suberged", more like "melted", although the dense stuff delivered by the impactor sank into the core.
"The last part is the most important to this article, as there are very very few "rocks" that can survive that sort of hear/pressure without being changed beyond recognition. One of these is Zircon."
Zircon isn't a rock, it's a mineral found in rocks, usually at a percent or less by volume, and it is harder than most minerals to "reset" it by heating. The rock in question is described as an amphibolite (a rock rich in minerals of the amphibole group, although they describe it as a "faux amphibolite", so it's an odd one). Zircon is relevant to the story because it contains uranium, and it is therefore a useful mineral for the U/Pb radiometric dating technique.
The really exciting part is that these rocks also have quartz and magnetite (Fe3O4) layers implying they were originally layered, sedimentary rocks (they've subsequently been heated and compressed to form a metamorphic rock, but the sedimentary signatures are apparently still there). Previously there were only individual mineral grains known that old (also zircons), with the rest of the rock heated and deformed subsequently so that little of the original structure remained.
"The belief is that these were either formed on earth prior to the impact or came on the thing that hit us (I can't remember which)."
They formed on Earth after the Moon-forming impact. That's thought to have occurred within the first 100 million years or so of Earth history, and there are no intact mineral grains on Earth that old (so far), and none are really expected because so much was melted by the event. For older stuff you have to look at meteorites.
There is a process called fission track dating that actually counts the number of paths of alpha particles through the crystal structure (think helium nuclei being shot out into the crystal and leaving destruction in their wake), which represents the number of decays. But this is rarely done in zircon, it is more typical in minerals like apatite, sphene, and micas.
The dating process for zircon used most commonly on this type of rock is called TIMS (thermal ionization mass spectrometry), and this involves crushing a portion of the rock, separating zircon crystals, dissolving them in acid, separating out the U and Pb through a column chemistry process, and then using a TIMS to ionize the U and Pb, and measure the ratio between the different isotopes. Which actually yields 4 different dates for the zicron grain, which can be used to cross check one another.