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Author Topic:   Dating Question For Members
ringo
Member
Posts: 19530
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.8


Message 38 of 77 (610210)
03-28-2011 12:12 AM
Reply to: Message 36 by Buzsaw
03-27-2011 11:57 PM


Re: Related Dating Questions
Buszsaw writes:

Thus if a fossil was formed by the flood, 4500 years ago, the radioactive dating is going to date the older rock sediment formed by the organism and not the organism which formed what is being dated.


This has been said several times before but I'm going to say it one more time, to clarify it for myself if nothing else. It is not the sediment containing the fossil that is being dated. It is the igneous layers above and below the sediment that are being dated. Even if that sandwich is turned upside down so that the oldest layer is on the top and the youngest layer is on the bottom, the age of the sediment is still between the ages of the other two layers.


If you have nothing to say, you could have done so much more concisely. -- Dr Adequate

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ringo
Member
Posts: 19530
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.8


Message 49 of 77 (610363)
03-29-2011 10:53 AM
Reply to: Message 46 by Buzsaw
03-29-2011 9:23 AM


Re: Related Dating Questions
Buzsaw writes:

So it appears that what would ultimately determine the age of the fossil is whether the plate tectonic activity was relatively sudden via catastrophe or over the millions of years, inch by inch.


The igneous material above the fossil is younger than the fossil. The igneous material below the fossil is older than the fossil. It doesn't matter how quickly they were deposited.

It is possible for younger igneous material to intrude below the fossil but it's pretty unlikely that it would appear as a layer, neatly inserted between sedimentary layers. Even if it did, it would make the fossil appear younger, not older.


If you have nothing to say, you could have done so much more concisely. -- Dr Adequate

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ringo
Member
Posts: 19530
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.8


Message 57 of 77 (610398)
03-29-2011 3:53 PM
Reply to: Message 55 by Buzsaw
03-29-2011 3:24 PM


Re: Related Dating Questions
Buszsaw writes:

I would assume that plate tectonics would be one cause of the rise of the intrusive igneous from the mantel to above the fossil.


Plate tectonics are caused by the same forces that cause lava to extrude and magma to intrude.


If you have nothing to say, you could have done so much more concisely. -- Dr Adequate

This message is a reply to:
 Message 55 by Buzsaw, posted 03-29-2011 3:24 PM Buzsaw has replied

Replies to this message:
 Message 58 by Buzsaw, posted 03-29-2011 4:50 PM ringo has replied

  
ringo
Member
Posts: 19530
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.8


Message 60 of 77 (610413)
03-29-2011 5:36 PM
Reply to: Message 58 by Buzsaw
03-29-2011 4:50 PM


Re: Related Dating Questions
Buzsaw writes:

What forces cause the lava to rise to the extent that it raises the plates?


The plates don't "rise" per se. They "float", as it were, on the magma. The weight of the plates forces magma up into cracks in the plates. (Think of walking on a frozen-over puddle. The ice cracks and water comes up through the cracks.)

Buzsaw writes:

How far above the planet's mantel does the magma rise before it becomes cooled enough to harden into intrusive igneous rock?


The magma can harden inside the rocks of the crust, in which case it is an intrusion, or it can harden outside the crust as lava, in which case it is an extrusion. Geologists can tell the difference between an intrusion and an extrusion. Only the extrusions would be used as dating layers.

Buzsaw writes:

If it is the cooled magma rock that is tested by the radiometric dating, does it date differently than the rising magma and if so, why?


The rate of cooling would depend on the initial temperature of the magma/lava, the temperature of the surrounding material, etc. My guess is that lava on the surface would cool more rapidly than magma below the surface.

But it's the sequence of the layers that matters, not the rate of cooling. The bottom layer would have cooled to the point of closure before sedimentary layers were deposited on top of it, so the lower layer will always date older than the higher layer.


If you have nothing to say, you could have done so much more concisely. -- Dr Adequate

This message is a reply to:
 Message 58 by Buzsaw, posted 03-29-2011 4:50 PM Buzsaw has seen this message

Replies to this message:
 Message 61 by JonF, posted 03-29-2011 6:12 PM ringo has replied

  
ringo
Member
Posts: 19530
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 2.8


Message 62 of 77 (610418)
03-29-2011 6:37 PM
Reply to: Message 61 by JonF
03-29-2011 6:12 PM


Re: Related Dating Questions
JonF writes:

Yeah, this will probably confuse Buz, but intrusive layers are used for dating where appropriate:


At least that photo makes pretty clear the difference between an intrusion and superimposed layers.


If you have nothing to say, you could have done so much more concisely. -- Dr Adequate

This message is a reply to:
 Message 61 by JonF, posted 03-29-2011 6:12 PM JonF has taken no action

  
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