Age of the Earth 2

[Bread_of_Life]

Background

For beginners, "radiometric dating" of rocks is a process that scientists use to tell how old rocks are. Radioactive elements in a rock when it is formed will decay into stable (daughter) elements at a predictable rate over it's lifetime - allowing scientists to pick the tock up at a later date, and tell how old it is by measuring how much radioactive element has decayed.

One particularly useful and accurate form of radiometric dating is called "Isochron" dating. Whilst some methods of radiometric dating have to approximate how much radioactive element was present to start off with, Isochron methods can actually find out scientifically. Also, most methods of radiometric dating assume that no daughter element or parent element have been introduced or escaped since the rocks formation, however, Isochron dating can test that too. Here's how:

Rubidium and Strontium

One of the most commonly used methods of Isochron dating is called the Rubidium-Strontium method. Rubidium-87 decays to Strontium-87, which is stable. Rubidium-87 has a half life of 48.8 billion years - that means that after 48.8 billion years, one kilo of rubidium would decay to 500g of rubidium.

Important facts about Rubidium and Strontium

Strontium exists in several forms. It exists in Strontium-87, but also in the form of Strontium-86. Importantly, when rocks are formed, the ratio of Sr-86 to Sr-87 is constant, that is: -

Sr-87 / Sr-86 = the same throughout the rock.

This is an observed (and theoretically predicted) fact. Strontium-86 is not ever the product of Rubidium-87 decay - Rb-87 only decays to Sr-87.

How the method works

When a rock solidifies, there will be different starting ammount of Rb-87, Sr-87 and Sr-86. However, everywhere in the rock the ratio Sr-87/Sr-86 will be the same. Imagine we split the rock into 6 parts, just after it is formed, and test each part. Fig. 1 on this website is a graph of what we'd come up with:

http://nikolai.faithweb.com/rbst.htm

As you can see, on the Y-axis (or left hand axis) we have Sr-87/Sr-86 - which as we now know is a constant. However, because there are different ammounts of Rb-87 in the rock, the Rb-87/Sr-86 on the X-axis is of different values for each of the 6 parts of the rock tested. By the way, this line graph is called an "isochron", that's where the method gets it's name!

What happens to the rock after it's formed?

Well, lets imagine we glue the rock back together, and leave it for a long long time, as 2 billion years. What would have happened over those two billion years? Well, the simple answer is, some of the Rb-87 in each part of the rock would have decayed to Sr-87.

Now look at Fig. 2 on the previously linked website. As you can see, each part of the rock has lost Rb-87, and gained Sr-87, hence a loss on the X-axis, but a gain on the Y-axis. Furthermore, because the ammount of Sr-87 gained is directly proportional to the ammount of Rb-87 lost, we've still got a straight line. In other words, the parts of the rock that had a lot of Rb-87 to start with have gained lots of Sr-87, whilst the parts with little Rb-87 have gained little Sr-87, hence we still have a straight line.

Now look at Fig. 3. This is what we'd find it we tested the rock after 2 billion years. The gradient of the line, as the more observant of you may have noticed, is proportional to how much time the rock has been decaying. So the steeper the line, the longer the rock's been there, the shallower the line, the shorter the rocks been there.

What is so clever about this method then?

Good question. The reason it's clever is because it deals with some of the assumptions and errors that other forms of radiometric dating are prone to. For example:

What if Rb87, Sr87 or Sr86 has leaked/entered the rock since the start?

Very simple answer to this one. Can you guess it? Well, the answer is, we don't get a straight line. If any part or parts of the rock have been tampered with, in any way, it would be statistically impossible that we'd get a straight line at the end of the day, hence, we'd know its been tampered with.

Sometimes scientists do find rocks that have been tampered with, and discard them because they are clearly unsuitable. Creationists try to trick people into thinking that the scientists are calling the rocks "unsuitable" because they don't agree with the age the scientists wanted the rock to be. Nothing could be further from the truth. Actually, the reason scientists are able to tell if a rock is unsuitable is because they've come up with a method of dating so clever, it even tests all it's assumptions.

What if the rock has melted and then formed again?

Another very simple answer to this one. Anyone guessed? The answer is, the isochron resets to zero. So actually, if the rock's been melted and then reformed, we'll get the date from when it's reformed, because each time it melts and reforms, the isochron resets. Clever eh?

But you still can't tell how much parent and daughter were in the rock to start with?

Firstly, in this case, it doesn't really matter, because all we need is the gradient. But actually, we *can* find out how much daughter and parent was in the rock to start off with (meaning that we can calibrate this method of dating). Any guesses how we do this?

Simple really, all we do is find the point where the graph cuts through the Y-axis, and that'll give us the original Sr-87/Sr-86. Having found the original Sr-87 concentration, it's easy to find, for each part of the rock, how much Rb-87 we started off with.

How cool is this method of radiometric dating?

The answer, on a scale of 1 to cool, this method is pretty darn cool. It checks every assumption, calibrates itself, tells us when the rock's been interfered with, and is totally foolproof even if the rock melts.

Now, I'm sure you're all really impressed, but does the method really work in practice, or have I been telling porky pies? The answer is a big massive yes! If you want pictures of real isochrons, I can scan em up and put em on the boards. I even have some pictures of unsuitable isochrons, where the rock has been tampered with, just to show you what happens if you want them.

Anyway, I'm sure you've had just about enough of me, so feel free to respond and ask questions, I've probably confused you enough!

[mobile21]

Excuse me ScientificAtheist, can you tell us how this "copying and pasting" will prove God doesn't exist?.

We know God can't be proved or disproved by science because science only works with measurable things and the revealed God of judaism/christianity is not measurable (the "gods" of pagan religions were measurable, for example the greek gods lived "on top of Mt. Olympus").

Unless you truly have a way to prove "through science" God doesn't exist, I don't see the point of all of this copying and pasting.

[nebula]

Folks -

I don't see SA trying to "disprove God's existance." He's just trying to show that the Earth is old.

[His son]

The Truth is he is trying to proove a lie. There are many many scientists who have proven that that dating system is the same as the evolution thing, it is only a theory made up by man to support a theory made up by man, and the same holds true of every fact the evolutionists claim. The true scientists have proven the 6 day creation.

[Cerran]

The Truth is he is trying to proove a lie. There are many many scientists who have proven that that dating system is the same as the evolution thing, it is only a theory made up by man to support a theory made up by man, and the same holds true of every fact the evolutionists claim. The true scientists have proven the 6 day creation.

Ahh the ol' ostirch syndrome, If I don't see it it isn't there. Truth is truth no matter which way you slice it. Replys like this not only demean christians and make us look like idiots, but they also do the bible and it's teachings a great disservice.

[Bread_of_Life]

Mobile21

FIrstly, you're right that this is a copy and paste. It is a copy of my thread from another bulletin board (http://www.planetwisdom.com/cafe). It was written originally as a follow up to the previous thread I posted up, also a copy and paste, from the same bulletin board. Notice for example, the website that is linked in with pictures of isochrons - that is my personal web-space.

Both posts were written by myself, fully, and intended to be read one after another - and understood at a beginner/intermediate level of scientific understanding.

Secondly, I am not attempting to prove that God doesn't exist. I am attempting to show that the earth is 5 billion years old. These are two rather different goals, and I wouldn't confuse the two if I were you. Therefore, if you're looking for a post that is going to disprove the existence of God, I would suggest you go elsewhere, this isn't it.

His Son

They certainly are theories, however, these particular theories have huge ammounts of evidence to support them. And they are believed not only by atheists, but by all religions and denominations.

Take this website for example, if you do not believe me:

http://www.asa3.org/ASA/resources/Wiens.html

It is written, as you can see, by a born-again evangelical Christian, who also believes in an old earth. He goes into detail about the same sorts of evidences I am presenting here.

[mobile21]

Secondly, I am not attempting to prove that God doesn't exist. I am attempting to show that the earth is 5 billion years old. These are two rather different goals, and I wouldn't confuse the two if I were you. Therefore, if you're looking for a post that is going to disprove the existence of God, I would suggest you go elsewhere, this isn't it.

Ok ok but because you declared yourself an atheist you must have already proven God doesn't exist right????.

Why don't you prove to us God doesn't exist instead of the age of the Earth????.

[Rerun]

Secondly, I am not attempting to prove that God doesn't exist. I am attempting to show that the earth is 5 billion years old. These are two rather different goals, and I wouldn't confuse the two if I were you. Therefore, if you're looking for a post that is going to disprove the existence of God, I would suggest you go elsewhere, this isn't it.

Ok ok but because you declared yourself an atheist you must have already proven God doesn't exist right????.

Why don't you prove to us God doesn't exist instead of the age of the Earth????.

Silly. He obviously didn't find enough evidence to suit his fancy. Thus he dismissed it. You've got to admit that although there are some hard facts proving the existence of God and his son, we must also resort back to our faith alot more. although the theory of the formation of the earth takes faith it's alot more feesable.

[Bread_of_Life]

Ok ok but because you declared yourself an atheist you must have already proven God doesn't exist right????.

Not so, I do not believe in leprechauns (I am an a-leprechaunist), but that doesn't mean that I can systematically disprove the possibility of their existence.

Why don't you prove to us God doesn't exist instead of the age of the Earth????.

I cannot prove that God doesn't exist - the burden of proof is in your court I'm afraid. Also, I am currently concentrating on science on this forum.

[Manofwork]

to this thread i add how long is a piece of string