Re: IIRC/response
wintermute, on host 24.209.9.85
Friday, May 12, 2006, at 07:02:02
Re: IIRC/response posted by LaZorra on Thursday, May 11, 2006, at 21:48:25:
> My other favorite is to have to sit in a geology lecture and be told by my college professor what an idiot I am for believing in Creation. This is while being taught that geologists date rock layers by the fossils in them
Rocks are dated by radiometric decay. For example, the amount of Potassium 40 that has decayed into Argon 40. Knowing the half-life of these decay, we can see how long it's been since the rock cooled down too much for argon to be able to escape. Sometimes, a tentative date can be set in the field by using index fossils, which must be distinctive, appear in a very small time frame, and (preferably) over a wide area. If we know that the rocks bearing a specific, distinctive type of clam have always turned out to be 70-80 million years old, then it's a fair assumption that this rock will, too. Any geologist worth his salt would be very excited to find that the index had a longer residency that previously known, though. So the date provided by these fossils is only an indication, and will not be considered accurate until backed up by radiometric dates.
Any geology teacher who claims index dating is the only (or even primary) method of dating rocks really shouldn't be teaching. It's roughly equivilent to a physics teacher saying that gravity works because solid objects are made of elemental earth and want to rejoin the Earth.
> and, in another part of the semester, being taught that fossils are dated (partially) by which rock layer they are found in.
Fossils are dated entirely by the rock layer they're found in. We have no other way of knowing how old they are, as all biological material has generally been replaced with minerals.
> And then learning that there is no place on earth where these rock layers are in their "correct" age order but are, in fact, often inverted in *exactly* the opposite order.
There are over 20 sites in the world where drilling cores have found every single geological period, from the Precambrian to the Holocence, in the correct order. I have never heard of the entire sequence being inverted, and I would love to find out more about it, if you can provide details, especially if it's not accompanied by obvious signs of folding.
> Or found containing fossils "several million years younger" than the layers themselves are thought to be.
If there was as much circular reasoning between geologists and palientologists as you were taught, how would anyone ever know that?
In truth, it's quite common to find fossils older than the rock they're in, as they get eroded out of the rock they were formed in, and redeposited in newer rock. If a fossil is found in rock older than the fossil is (presumably, older than than minerals that have infilled the fossil) then that would be very exciting.
> Again, this is all from my personal experience. If what I know is incorrect, feel free to correct me.
If you insist.
> LaZ
winter"geology geek"mute
|