Re: [asa] geological dating

Evolution doesn't necessarily imply common descent.

If you have organisms coming into and passing out of existence in the order we observe, you have evolution, whether or not it all happened by special creation. No one can say in detail what God's role was in this evolution we know, and it's possible that he caused much to happen that would not have happened without his special action. So indeed every organism could be a special creation in some sense.

[Science cannot legitimately say that the biotic world is not an infinitude of special creations, but it would be in complete violation of its methods and principles to say that it is. The role of scientists is to see how far they can go in explaining things without invoking special creations and creator(s).]

In any case the utility of index fossils is evidence for evolution and would be inconceivable without evolution.

The possibility of special creations opens the possibility of kinds of order that are radically different from the one we observe. If the actual order had organisms oscillating between emergence and extinction, then of course there would likely be no useful index fossils. An oscillating biosphere would constitute a whole other kind of evolution. The utility of index fossils depends on a particular kind of evolution, namely, monotonic--the kind we have.

[It's not obvious--and in fact curious--why an omnipotent, omniscient creator would choose this monotonic approach out of all available possibilities.]

As for age range, index fossils can only indicate an upper limit of age. It's always possible that index fossils will turn up in formations younger than the formations where they first appeared, even if their organisms quickly went extinct: Sedimentary rocks can be "reworked."

Trilobites from Cambrian to Permian did not constitute a single index. There's great variation among the 17000 known species of trilobites--as also among brachiopods. Not all lived at the same time.

Don

  ----- Original Message -----
  From: skrogh<mailto:panterragroup@mindspring.com>
  To: asa<mailto:asa@calvin.edu>
  Sent: Wednesday, October 14, 2009 8:21 AM
  Subject: RE: [asa] geological dating

  Sure you would. Even if evolution (common descent) didn't exist, and it was all individual little creation events that brought the life forms into being in a certain observed order, it wouldn't change the "index-ness." This is getting the kart before the horse. Without evolution, you would still be able to say this. What you wouldn't be able to say is that fossil x could have developed from a certain lineage. Since index fossils do indeed exist, it doesn't matter. Index fossils are only reliable in relative dating until that fossil is found outside it's former range, and only tentative. I did a study on the very unassuming brachiopod Kingena wacoensis, which was later named Waconella wacoensis. This brach was only considered an index fossil because its high reliability in what formation it just happened to be observed (Georgetown Formation of the Cretaceous) and it has never been observed outside of this formation. The idea of common descent has no bearing on it being an index fossil, only that it has never been observed outside of the Georgetown Formation. If it is observed outside the formation, the formation wouldn't be expanded to include the fossil, but rather the age range of the fossil would be expanded to accommodate the new find and it would simply no longer be considered an index fossil for a specific formation. It may be considered an index like trilobites which spans from Cambrian to Permian.

   -----Original Message-----
  From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu]On Behalf Of Don Winterstein
  Sent: Wednesday, October 14, 2009 9:03 AM
  To: asa
  Subject: Re: [asa] geological dating

    "evolution is not integral to the dating...."

    Index fossils are widely used for relative dating of rocks, so in that sense evolution is integral to such dating. That is, if you find fossil x, you know that the formation is no older than the time at which fossil x first appeared. Without evolution you wouldn't be able to say this.

    Don

      ----- Original Message -----
      From: David Campbell<mailto:pleuronaia@gmail.com>
      To: asa@calvin.edu<mailto:asa@calvin.edu>
      Sent: Tuesday, October 13, 2009 10:08 AM
      Subject: Re: [asa] geological dating

      A couple of minor caveats:

      In addition to 14C, there are some fossils containing radioisotopes
      that can be used for dating. For example, corals often contain enough
      thorium to date, and various types of replacement may involve
      radioactive elements , e.g., the often uranium-rich dinosaur bones in
      parts of the western U.S. or glauconitic molds of marine organisms
      (though of course, the date will reflect when the replacement
      occurred, not the original organism, and glauconite has a number of
      issues).

      However, in general an igneous rock is the best for radiometric
      dating. (A metamorphic high-pressure carbon isomorph might do better
      for some other dating). Obtain dates on several different minerals
      and isotopes from a single rock, and you've got a very
      well-constrained age, with the caveat that a given rock may
      crystallize slowly. A volcanic ash layer associated with fossils is
      thus about the best-case scenario for dating.

      All sorts of long-term trends or variations can provide relative dates
      and then be calibrated with radiometric dates. These include, among
      others, changes in stable isotope ratios, magnetic reversals,
      Milankovitch cycle-related changes, impact layers, and evolution. The
      evolution is not integral to the dating; it just is the explanation
      for why you see change in organisms over time and can therefore be
      confident that, e.g., a layer with Chesapecten jeffersonius is older
      than a layer with low rib count Chesapecten madisonius, which is older
      than normal Chesapecten madisonius, just as we know that an undated
      scrap of paper that identified Jefferson as the current president
      would be older than one citing Madison as the current president.

      --
      Dr. David Campbell
      425 Scientific Collections
      University of Alabama
      "I think of my happy condition, surrounded by acres of clams"

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Received on Sat Oct 17 03:41:09 2009