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."

Comments

Discovery of world's oldest rocks challenged (link

[Anonymous Coward]

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

Re:4 Billion years old? I don't think so.

[dakameleon]

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 Bible itself speaks to us of the origin of the universe and its make-up, not in order to provide us with a scientific treatise, but in order to state the correct relationships of man with God and with the universe.

... pointing out that the Pope does not consider it to be taken literally;

Sacred Scripture wishes simply to declare that the world was created by God, and in order to teach this truth it expresses itself in the terms of the cosmology in use at the time of the writer.

... pointing out that it was written for an audience, not an 'absolute truth';

The Sacred Book likewise wishes to tell men that the world was not created as the seat of the gods, as was taught by other cosmogonies and cosmologies, but was rather created for the service of man and the glory of God.

... pointing out that its purpose is to put forward the 'Christian'/monotheistic view, as opposed to the views of other religions, such as the contempary polytheistic religion of the Romans, and again not altogether incompatible with science.

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.

Re:Discovery of world's oldest rocks challenged (l

[rockhopjohn]

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.

Re:Worlds oldest found rocks found!

[Anonymous Coward]

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.