The age of Rocks

[anunbeliever]

Please excuse my ignorance of geology. I saw a doco the other day where someone was speaking of a rock in Australia thought to be over 4 billion years old. Now i know plate techtonics is a slow process, but 4 billion years is a very long time. Wouldn't every part of the Earth have been subducted and re-extruded many times over such a long period?

 

[L'Anatra]

Please excuse my ignorance of geology. I saw a doco the other day where someone was speaking of a rock in Australia thought to be over 4 billion years old. Now i know plate techtonics is a slow process, but 4 billion years is a very long time. Wouldn't every part of the Earth have been subducted and re-extruded many times over such a long period?

I'm no geologist either, but I don't see why certain parts of the crust near the surface couldn't be 4 billion years old. Obviously most of it going to be a bit younger.

Hopefully Mechanical Bliss or someone else with some knowledge of geology pops in here.

 

[Valkhorn]

Well since I know a bit about Geology, I'd like to step in.

Rocks are usually dated by process called Radiometric dating. Radiometric dating is based on the principle that when a rock is solidified into magma, isotopes that are part of the constituent of the rock start to decay.

From http://www2.nature.nps.gov/geology/usgsnps/gtime/radiom.html

[font=TIMES NEW ROMAN,TIMES, SERIF] Radioactive elements were incorporated into the Earth when the Solar System formed. All rocks and minerals contain tiny amounts of these radioactive elements. Radioactive elements are unstable; they breakdown spontaneously into more stable atoms over time, a process known as radioactive decay. Radioactive decay occurs at a constant rate, specific to each radioactive isotope. Since the 1950s, geologists have used radioactive elements as natural "clocks" for determining numerical ages of certain types of rocks.

Radiometric clocks are "set" when each rock forms. "Forms" means the moment an igneous rock solidifies from magma, a sedimentary rock layer is deposited, or a rock heated by metamorphism cools off. It's this resetting process that gives us the ability to date rocks that formed at different times in earth history. [/font]

So really, the dating of a rock can pretty much tell us how old it is since it first cooled/crystalized from magma.

Now what kinds of dating can be used? To determine the age of anything with radiometric decay we need to know the half-life of a particular isotope. Some half-lives are very short, while others are very long:

Now, notice that some isotopes have very short half-lives, while others have very long half-lives. Take a look, especially, at Potassium-40. Its halflife is 1.3 billion years.

Actually Potassium40 dating is a method used in dating some rocks. By determining the percentage that hasn't decayed, we can see how old a rock is:

So, you see, by determining how much of the Potassium-40 has broken down into Argon-40 you can determine how much time there has been since the formation of said rock.

Now, how is it that we have found rocks and crystals to be over 4 billion years old, like this one?
http://www.news.wisc.edu/10849.html

Well chances are, it is simply a matter of coincidence. A very old rock could have been underground and away from the elements for a very long time. It could have been in a region that saw no volcanic activity - like in the middle of a continental craton for a very long time. So long as the circumstances warrant it, rocks can be that old.

Hope this answers your question?
​

 

[Mechanical Bliss]

Please excuse my ignorance of geology. I saw a doco the other day where someone was speaking of a rock in Australia thought to be over 4 billion years old. Now i know plate techtonics is a slow process, but 4 billion years is a very long time. Wouldn't every part of the Earth have been subducted and re-extruded many times over such a long period?

This recycling of the crust occurs in the oceans. Oceanic crust has a greater density than continental crust, which is why it "sits" lower on the mantle than the continents in the first place, and along with thermal differences between ridges and trenches, this is why oceanic crust is what is subducted and extruded rather than continental crust.

Mountain ranges are a good example of continental crust not subducting. When the oceanic crust between two continents is subducted, the continental crust does not follow. It is effectively pushed up as the subduction continues, but it is not dense enough to be subducted itself.

This is why the oldest continental crust is about 4 billion years old or so and the oldest oceanic crust is only about 220-250 million years old.

 

[Dr.GH]

opps

 

[Dr.GH]

There were already several good responses. Just to fill in a few gaps;

The oldest objects we currently are aware of that are of terrestrial origin are zircon crystals that are found preserved in quartzite. Quartzite is metamorphic sandstone. Zircons are much more resistant to recrystalization than quartz crystals which is how they survive the recrystalization of quartz grains (sand) into quartzite.

Zircon forms in an ingneous melt, and can be quite common in some igneous rock (eg. syenite) and has a high concentration of Uranium and its decay products (thorium and lead). Syenite itself is mostly formed from the mineral feldspar, or plagioclase and has very little to no native quartz.

Now you can see why the zircon grains in quartzite are typically much, much older than the rock they are found in as they are the product of multiple geologic processes: the original crystalization in syenite (or other appropriate plutonic melt). The pluton must then be brought to the surface and the zircon must then be weathered out. The freed zircon then must be bedded into a quartz sand bed that is cemented into a sandstone mass. The sandstone, in turn, is reburied where it is recrystalized under high temperature and pressure into quartzite. (Rapid heating that forms metavolcanic quartzite which is more likely to destroy the zircon). The quartzite must then become reexposed and available for samples.

The heating of the metamorphic process does alter the outer portion of the zircon, and so great care in proper sample selection and analysis is needed.

"Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth" E. B. Watson and T. M. Harrison. Science 6 May 2005; 308: 841-844 [DOI: 10.1126/science.1110873] (in Reports)

There is a very good illustration of this in the article referenced above:

This shows the locations for both the age determination and the use of titanium isotopes to establish the temperature under which the zircon formed. This particular zircon from Western Australia's Jack Hills was 4.2 billion years old (4.2 Ga).

 

[GodsSamus]

Please excuse my ignorance of geology. I saw a doco the other day where someone was speaking of a rock in Australia thought to be over 4 billion years old. Now i know plate techtonics is a slow process, but 4 billion years is a very long time. Wouldn't every part of the Earth have been subducted and re-extruded many times over such a long period?

In my honest opinion, you're being lied to about the ages of the rocks. They use the fossils to tell how old the rocks are, then they use the rock layers to tell how old some of the non-index fossils are.

 

[Peris]

theres no fossils in 4 billion year old rocks afaik

 

[Mechanical Bliss]

In my honest opinion, you're being lied to about the ages of the rocks.

Your opinion is meaningless because it is based upon a total lack of knowledge of any of the science relevant to this question.

They use the fossils to tell how old the rocks are, then they use the rock layers to tell how old some of the non-index fossils are.

This is false, as has been explained to you several times before.

Either it's a lie or you don't read anyone's explanation of why your characterization of how rocks are dated is wrong. Either way, such behavior does not speak well for your credibility and does not facilitate others taking you seriously.

Once again, you illustrate you don't know much at all about the relevant sciences here. You just repeat catchphrases from creationist websites and pretend like the refutations of such understandings haven't been presented for your benefit numerous times already.

 

[notto]

In my honest opinion, you're being lied to about the ages of the rocks. They use the fossils to tell how old the rocks are, then they use the rock layers to tell how old some of the non-index fossils are.

Can you show us where it discusses fossils in any of the great material that has been given already in this thread that discusses how rocks are dated?

Why do you continue to repeat things that have already been exposed to you as being false and accuse others of being lied to?

You have been shown that it is YOU who have been lied to and you continue to repeat these lies.

 

[Dr.GH]

There are a number of good books on radiometric dating. The best single source for people without much chemistry background is G. Brent Dalrymple's, 1991 The Age of the Earth (Stanford: Stanford University Press). There have been major intrumentation improvements since Dalrymple's book was published, but the basics are all still the same.

PS: if we can believe GodsSamus, he is a 10 year old kid from Texas. 'Nuff said.

 

[GodsSamus]

Sounds like you can't resort to evidence to support your religion, so you need to rely on INSULTS. Hardly science.

 

[Valkhorn]

Sounds like you can't resort to evidence to support your religion, so you need to rely on INSULTS. Hardly science.

Um we did rely on evidence.

You did not.

Wake up and smell the coffee.

Oh yeah, and its not a religion.

 

[GodsSamus]

Um we did rely on evidence.

You did not.

Wake up and smell the coffee.

Oh yeah, and its not a religion.

Let's see. You rely on the Talkorigins web site, even after I point out it's fallicies and circularity, whereas I used the magnetic field, the shrinking sun, the receeding moon, the erosion of continents, the global flood legends, and numerous other evidences, yet I didn't use any evidence?

If Evolution's a religion, why hasn't it been thrown out as a bad theory? NOWHERE does the Geologic Column exist, that you worship (It's your Bible, but who wants to carry a 100-mile-tall pile of rocks?). Numerous finds destroy it, such as the pictures of dinosaurs, Ica stones, Dragon legends, etc.

 

[Elduran]

Let's see. You rely on the Talkorigins web site, even after I point out it's fallicies and circularity,

And your claims are constantly refuted, then you ignore the rebuttals and pretend that you haven't been challenged at all.

whereas I used the magnetic field, the shrinking sun, the receeding moon, the erosion of continents, the global flood legends, and numerous other evidences, yet I didn't use any evidence?

See above.

If Evolution's a religion,

It isn't

why hasn't it been thrown out as a bad theory?

Because NO-ONE has refuted it with good evidence. There's a lot of anecdotal evidence and creationist mumbo-jumbo, but no real evidence other than clamping hands over ears and closing eyes tight and ignoring real evidence.

 

[Peris]

Let's see. You rely on the Talkorigins web site, even after I point out it's fallicies and circularity, whereas I used the magnetic field, the shrinking sun, the receeding moon, the erosion of continents, the global flood legends, and numerous other evidences, yet I didn't use any evidence?

If Evolution's a religion, why hasn't it been thrown out as a bad theory? NOWHERE does the Geologic Column exist, that you worship (It's your Bible, but who wants to carry a 100-mile-tall pile of rocks?). Numerous finds destroy it, such as the pictures of dinosaurs, Ica stones, Dragon legends, etc.

your 'fallacies' have been refuted many times here, with sources mentioned other than talkorigins, why do you still cling to them?

Evolution is not a religion, it's a well supported scientific theory that has withstood more than a century of falsifying attempts. If you know the key to falsify evolution, why don't you start submitting your ideas to scientific journals (which i bet you don't even read)? A noble prize probably awaits you if you can prove evolution to be wrong.
How do your numerous finds destroy it? The ica stones have been proved to be fakes (as has been pointed out many times on these forums, with sources mentioned), dragon legends are what they are... legends. You probably believe unicorns once roamed the earth too right?

 

[notto]

Sounds like you can't resort to evidence to support your religion, so you need to rely on INSULTS. Hardly science.

Can you show us where it discusses fossils in any of the great material that has been given already in this thread that discusses how rocks are dated?

Your statement is false. Why do you say things that are false and accuse others of lieing?

 

[Grengor]

If he doesn't, he might "lose".

 

[Mechanical Bliss]

Sounds like you can't resort to evidence to support your religion, so you need to rely on INSULTS. Hardly science.

Continuing with this dishonesty does nothing but dig you in a deeper hole.

Evidence has been provided previously for your benefit:

(a) that demonstrates your accusation of circular reasoning to be wrong
(b) that demonstrates the earth to be much older than 6 ky
(c) that demonstrates the reliability of radiometric dating

Why should we present this evidence again when you're just going to ignore it yet again then turn around and make the same assertion all over again as if nothing happened?

And never mind the fact that the amount of evidence you brought to this discussion (and others) is NONE.

 

[Mechanical Bliss]

Let's see. You rely on the Talkorigins web site,

I don't recall any links to talkorigins in this thread.

Our reliance is on the scientific evidence, which is supported by talkorigins, but obviously not only talkorigins.

even after I point out it's fallicies and circularity,

You have done nothing of the sort. Simply making that claim does not "point out" anything.

whereas I used the magnetic field, the shrinking sun, the receeding moon, the erosion of continents, the global flood legends, and numerous other evidences, yet I didn't use any evidence?

You have used zero evidence in this thread, as others. You have used these arguments in previous threads and had them refuted. That you still use them means you either don't read others' posts or are unwilling to admit your error.

If Evolution's a religion, why hasn't it been thrown out as a bad theory?

Evolution is not a religion, so that's why first of all. Second, nothing in this thread has anything to do with evolution.

This only shows that this is purely emotional to you which is why you brought big, bad evolution into this thread when it has nothing to do with it.

NOWHERE does the Geologic Column exist, that you worship (It's your Bible, but who wants to carry a 100-mile-tall pile of rocks?).

It has been explained to you before that geologists don't even think a singular geologic column exists in the first place. The only scenario under which we should expect such an occurrance is if a global flood occurred. You refute yourself with that argument.

This is a strawman argument that only demonstrates that you don't have the slightest clue what you're saying.

Again you are repeating things that have been addressed for your benefit previously. It is dishonest to continue with the same arguments after having been refuted before.

Numerous finds destroy it, such as the pictures of dinosaurs, Ica stones, Dragon legends, etc.

It's been pointed out to you several times before that the Ica stones are fraudulent.