Methods of Dating

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Hi all,

I'm new here and have a rather simple question... how are objects in the earth's crust, such as fossils, dated? I understand that 40,000-65,000 years is the average availability of years that certain organic materials can be dated with carbon-14 dating, so how are numbers of years such as the arrival of the dinosaurs 250 million years ago discovered?

This is a topic my uncle and I frequently argue on. He's a fundamentalist Christian and states the earth is around 10,000 years old (something I get nearly furious with every time we discuss the issue) and of course this statement isn't based on science, but I wouldn't know how to respond if he asked me HOW we know that dinosaurs first walked the earth 250 million years ago.

I apologize if this is an extremely mundane topic for most of you (I imagine it is) and that if it gets in the way of many more complex issues.

Thanks,
C.J.
 

Answers and Replies

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Last edited:
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Hi all,

I'm new here and have a rather simple question... how are objects in the earth's crust, such as fossils, dated? I understand that 40,000-65,000 years is the average availability of years that certain organic materials can be dated with carbon-14 dating, so how are numbers of years such as the arrival of the dinosaurs 250 million years ago discovered?

This is a topic my uncle and I frequently argue on. He's a fundamentalist Christian and states the earth is around 10,000 years old (something I get nearly furious with every time we discuss the issue) and of course this statement isn't based on science, but I wouldn't know how to respond if he asked me HOW we know that dinosaurs first walked the earth 250 million years ago.

I apologize if this is an extremely mundane topic for most of you (I imagine it is) and that if it gets in the way of many more complex issues.

Thanks,
C.J.
The answer is simple, Potassium-Argon Dating
http://en.wikipedia.org/wiki/Potassium_argon_dating
 
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The following quoted text is from this article: http://www.answersingenesis.org/docs2002/carbon_dating.asp" [Broken]

This is the basis for your Uncle's argument.

There are various other radiometric dating methods used today to give ages of millions or billions of years for rocks. These techniques, unlike carbon dating, mostly use the relative concentrations of parent and daughter products in radioactive decay chains. For example, potassium-40 decays to argon-40; uranium-238 decays to lead-206 via other elements like radium; uranium-235 decays to lead-207; rubidium-87 decays to strontium-87; etc. These techniques are applied to igneous rocks, and are normally seen as giving the time since solidification.

The isotope concentrations can be measured very accurately, but isotope concentrations are not dates. To derive ages from such measurements, unprovable assumptions have to be made such as:

1. The starting conditions are known (for example, that there was no daughter isotope present at the start, or that we know how much was there).

2. Decay rates have always been constant.

3. Systems were closed or isolated so that no parent or daughter isotopes were lost or added.
 
Last edited by a moderator:
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Weell obviously isotope ratios are the answer. But it's interesting to note that some christian scientists propose that god (or some other mighty force) sped up the decay rates to give the illusion that these things are older.

Clutching at straws if you ask me, but it's something your uncle might say.
 
Rach3
Please change the thread title, it's false advertisment! Thanks.
 

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