Ancient Skull Challenges Human Origins

Annabel Lee · Jul 10, 2002

Originally posted by unworthyone
LOL. Thanks Seebs. Remember now I don't advocate creation or evolution. I just like to read about it.

LOL..Admit it my Worthy friend..You're a closet evolutionist.

Come to the DARK SIDE!

unworthyone · Jul 10, 2002

Originally posted by Annabel Lee

LOL..Admit it my Worthy friend..You're a closet evolutionist.

Come to the DARK SIDE!

LOL. Maybe so. Who knows though right?

unworthyone · Jul 10, 2002

I guess my problem is how can you say a dating method is accurate if you don't know by objective proof of how old the reference is.

Like if I left out a glass of milk in open air for 40 days its obviously older then the milk I just poured.

How do we know the dating method is right if you are using a different method to prove it?

Jerry Smith · Jul 10, 2002

Originally posted by unworthyone
Okay i think understand now and thanks guys for telling me that.

Now how did they come to the conclusion that that dating method was correct for that layer and that rock? What reference was used?

I'm asking because you are describing in laymans terms and I'm understanding it somewhat....nobody ever wants to do that.

I hate jumping into the middle of someone else's hypothetical, but Ar/Ar dating is accurate when used for a wide range of rocks. Because it is more reliable than (for instance) K/Ar, it is preferable (even though the accuarate range of K/Ar somewhat overlaps Ar/Ar). If the rocks were very young (less than 100 thousand years old), some other method would most likely be preferable. IIRC Ar/Ar is one that works with some accuracy to even the oldest rocks found on earth.

There are numerous radioisotopic choices for most rocks: You choose the ones that:

have the tightest "error bars" for the estimated age of what you are dating,
Are not compromised by evidence of contamination or leeching of the isotopes in use... (I cannot explain the various ways they have for determining this..), and
that the cost merits (If knowing the age to +/- 1 million years is not very important and you can save twenty grand by using a method that gives results to +/- 5 million years, you might choose the latter option)

unworthyone · Jul 10, 2002

But what are they using as reference that they know is, for instance, 20 million years old?

Does my milk analogy make sense?

Aren't they just using one method to validate another method?

seebs · Jul 10, 2002

Originally posted by unworthyone
I guess my problem is how can you say a dating method is accurate if you don't know by objective proof of how old the reference is.

Comparisons, mostly. You can end up with something where you have a *LOT* of data points known to be roughly from the same time, and you date all of 'em, and you get similar answers... you can also compare with other dating techniques.

If you want a way to think about this, imagine that you have a bunch of strings, some of them fairly stretchy, and others not so stretchy, each divided into units; if you practice measuring things with them, you quickly get a feel for which of them are the most consistent, and from that, you can start forming a reasonable overall picture of their measurement qualities.

Jerry Smith · Jul 10, 2002

I guess my problem is how can you say a dating method is accurate if you don't know by objective proof of how old the reference is.

Like if I left out a glass of milk in open air for 40 days its obviously older then the milk I just poured.

How do we know the dating method is right if you are using a different method to prove it?

But what are they using as reference that they know is, for instance, 20 million years old?

Does my milk analogy make sense?

It does, but I'm not sure it applies because of some "technical reasons".

Radiometric dating works because the rates of decay of any given isotope are known fairly precisely, and because decay rate is dependent only on the type of isotope used... Therefore the parent/daughter ratio can always be used to calculate the age... you are working from know decay rates. BUT, it can go wrong.

We have confidence in the method in general because it is based on well understood laws of physics. We need to validate the results by other methods because there is room for error due to contamination or leeching. We can validate the results by using different radiometric methods and more than one sample. If Ar has leached out, a different isotope (Sr for instance) with different chemical properties will yield the "correct" date. Checking both against the age of the layer of rock as indicated by "index fossils" ones that have are only found in rocks of a certain age, would tell you which method was more likely correct. Checking multiple samples should give enough data points that any confusion is cleared up.

unworthyone · Jul 10, 2002

So they take one rock, measure 5-6 points on the rock, and accept the points that most accurately relate to their estimations gathered from another source which measured in the same manner, testing 5-6 points and excepting ones closest to the previous estimations?

How do we know the rate of decay has been consistent over the last 10 million years?

We can't even accurately determine the atmosphere of 500 years ago much less 10 million.

unworthyone · Jul 10, 2002

Hahah!! I'm looking it up myself and its just plain genius thinking. Well, I'm not a genius, so I'm not going to understand....

LOL!

Jerry Smith · Jul 10, 2002

How do we know the rate of decay has been consistent over the last 10 million years?

That is physics. We know how a radioactive element decays, and why. The nuclear structure and mass of the element is the only variable in its decay rate - everything else is based on constants (i.e. the speed of light).

testing 5-6 points and excepting ones closest to the previous estimations?

You test a few samples (depending on how much certainty and how much accuracy you are looking for). You take into account known issues (volcanic ash is more subject to certain kinds of error-producing anomalies than is granite -- perhaps granite is more subject to another kind that volcanic ash). You check to see if all dates are in agreement from the methods you used. You will almost always compare the stratigraphic date with at least one radiometric date. If the two do not agree, you have to account for the difference, or leave the date as an unknown. One way to account for the differences is to attempt to identify the source of the discrepancy. If you can do so, then you can safely discard the incorrect date - but you would still want to cross check your other date with a third method. Since there is no reason two or more methods should agree, apart from pure accident (which should be very rare, considering the available range of options for dates), except that the two methods are giving the correct date.

We have further confidence, because if decay rates had been changing over the last 10 million years, then a Sr/Rb test wouldn't yield the same date as an Ar/Ar test or any other test.

chickenman · Jul 10, 2002

i'm still waiting for npeterly to come in and make some bad joke and mention the word imagination about 50 times

Jerry Smith · Jul 10, 2002

Worthy,

I found this diagram, which might be helpful to you on some of your questions:

It is at http://pubs.usgs.gov/gip/geotime/ (Click the words: Table of Contents). This whole site should be intesting to you. It doesn't go into much depth or answer all of your questions, but it will add to your over-all knowledge and understanding of the geology aspect of this debate...

Another interesting page is here:
http://www.mdia.org/georock.htm

I have e-mailed someone who had posted a web-page chronicaling his own experience in the field of paleontology requesting his assistance in finding helpful material for you. I will let you know if he responds, and I do continue my search for helpful information from you.

Meantime, if you haven't ever done it - I encourage you to take a long gander at the talk origins archive.. you may be surprised at what you can find there.

unworthyone · Jul 10, 2002

Awesome. Thanks Jerry.

Jerry Smith · Jul 11, 2002

Here is one you might like worthy:
http://www.ucmp.berkeley.edu/cambrian/whites.html

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