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Author Topic:   Geologic Column
NosyNed
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Posts: 8971
From: Canada
Joined: 04-04-2003


Message 1 of 55 (38531)
05-01-2003 2:34 AM


There are a number of claims made by creationists about the geologic column.

Let's look at them one at at time.

Also, I didn't get the idea you knew this already (though I may be misunderstanding your first comment) but they DO NOT date fossils by radiometric decay--fossils are dated based on what layer of rock they are found in

from www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=228&m=15#15 -->www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=228&m=15#15">http://www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=228&m=15#15

in reply
You're caught in a misconception about dating with index fossils.

quote:
--------------------------------------------------------------------------------
Also, I didn't get the idea you knew this already (though I may be misunderstanding your first comment) but they DO NOT date fossils by radiometric decay--fossils are dated based on what layer of rock they are found in
--------------------------------------------------------------------------------

That's true but misleading. The fossils are part of the characteristics of rocks which were recognized centuries ago. They helped to sort out the layering. Some fossils are very restricted to what layers they are found it and make this easier but other characteristics of rocks help. This produced the geologic column with relative ages. Only relative.

A long time after that various methods became available to date the layers directly. This put absolute dates on the layers.

Now since the geologic column had already been sorted out and the fossils which could be used as index fossils for a layer already been determined it is easy to date a layer by looking the fossils. In any case where there is doubt about a date a direct dating can be done. The fossils help tell what layer you are looking at. The index fossils anyway. These layers are dated separately. Any other non-index fossils in the same layer can then be assigned the same date.
Got that?

Links:
http://earthsci.org/teacher/basicgeol/geotim/geotim.html
http://www.geol.umd.edu/~tholtz/G104/104Y2K/104Lec04.htm

I'll leave this for further posts with one note for the creationists to answer:

Historically the geologic column was worked out (starting with creation scientists) and the relative ages were assigned. Much, much later the absolute ages were determined with different radiometric methods.
Why did the absolute ages correlate with the relative ages previously worked out?


  
NosyNed
Member
Posts: 8971
From: Canada
Joined: 04-04-2003


Message 4 of 55 (86127)
02-13-2004 1:44 PM
Reply to: Message 3 by edge
08-16-2003 4:16 PM


A 60 second geologic primer
This is a bump for lunkhead.

I will try a quick summary.

In any one place in the world there may be a series of strata. These have particular kinds of rocks one a top the other.

Sometimes the layers are obviously "screwed up" as when a mountain range has risen and the layers are twisted and bent. However, even then the relationships may be intact. That is which layer is next to what layer.

When comparing layers from different places sometimes you find that a few of the layers from one place match up with layers from another. The nature of the rocks, the relationship between them, the kind of fossils in them and perhaps even some degree of thickness are the same. However, this new place may add (above or below) additional layers not found somewhere else.

If site after site (many 1,000's) are examined it becomes possible to find a clear pattern. Even without one place with all the layers it is clear what the sum of all strata would look like. (though there are places with all or a lot of it in one place).

All of this was done around two centuries ago.

Much, much later the technology became available to give absolute, rather than relative, dates to the layers.

Lo and behold, now pay attention, this part is important: The dates corresponded to the already determined order from deep down in the geologic column being old to high up being newer.

If anyone can doubt the validity of the overall result after that they have some serious information processing deficits.

Now the geolgists can please correct any big booboos I have made.

[This message has been edited by NosyNed, 02-13-2004]


This message is a reply to:
 Message 3 by edge, posted 08-16-2003 4:16 PM edge has not replied

Replies to this message:
 Message 5 by Bill Birkeland, posted 03-17-2004 1:10 PM NosyNed has not replied

  
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