>I must admit to being totally mystified by comments like this from
>you --- and they are not infrequent. For some points you insist that
>you are dealing with a rigid set of scientific rules -- -- that are
>used to date fossils -- and not the other way around.. Then things
>like the "mutation rate" become a variable --- and all the past
>dating is tossed into the air. Yet you suggest that everyone who
>does not agree with all this is not scientifically oriented.<
Despite the popularity of molecular clocks, mutation rate is clearly
variable. On the other hand, the rates of radioactive decay appear
totally constant (apart from those rates affected by local electron
density, which are not used for dating, and any possible variation in
the laws of physics immediately following the Big Bang). In theory,
molecular clocks are ultimately based on calibration from the fossil
record. When this calibration date is shown to be erroneous, the
molecular clocks must be revised.. (In practice, some molecular
clocks are based only on other molecular clocks or on something said
by another molecular biologist about the fossil record.) Of course,
a single calibration date produces a statistically meaningless
result. Despite all this, careful searching may turn up a sequence
with reasonably consistent mutation rates, and there are also broad
conclusions that may be gained from a variable mutation rate. For
example, a talk last summer used molecula!
r clocks to test the identification of various late Precambrian to
Cambrian fossils as representing modern groups of cnidarians. If the
molecular clock put the origin of the group more than about a hundred
million years after the fossils, the identification of the fossils as
belonging to the group was considered supect.
As a paleontologist, I am naturally more inclined to trust the fossil
record, but the statistical problems and poor paleontology of many
molecular clock papers certainly does not dispel my suspicion.
>Frankly all the changes of dates and methods that you keep throwing
>around make me have serious doubts about the scientific rigor
>practised in your field. You seem to a mental rule that: if the
>dating makes things happen earlier in time -- so as to fit your
>theory --- then it must be correct. Why should any technically
>oriented person believe (even tentatively) these theories if they
>keep changing from month to month?<
Glenn has the advantage in his position that new finds almost always
increase the age of something. Unless a new discovery proves that
the previous record holder was misdated or misidentified, the only
possible change in dating of the first known example of x is to find
an older one.
On the other hand, changes in the date for a particular fossil,
artefact, etc. are relatively rare. Improved correlation of the
Pliocene deposits in the eastern U.S. has moved the estimated age
from before 5 million to about 2.5 million to older than 3.8 million.
The move from before 5 to later reflected the initial studies of
planktonic microfossils, which are much safer as a basis for global
correlation than percent extinction (the previous method). 2.5
million represents a miscorrelation, in which fossils from one
locality were used to date a bed defined at another locality.
Between 5 and 3.8 million, probably close to 4 million, reflects a
more careful study on additional microfossils. These changes in
dating represent the last 30 years of study, plus some personal
conflicts.
The dating methods themselves have undergone relatively little change
since the introduction of radiometric dating. Technical refinements
and new material are responsible for most of the changes in dates.
A similar disadvantage holds true for young-earth advocates. If the
earth is old, any number of things may have happened quickly during
the long period of its existence. Thus, evidence that a particular
event happened rapidly is compatible with either a young earth or an
old earth view, but anything that took a long time is incompatible
with a young-earth view. The YEC is faced with the almost impossible
task of showing that everything in the geologic record happened
quickly and largely simultaneously. Likewise, a single clear piece
of evidence for human behavior dating from before the existence of
fully modern-looking humans is sufficient to cause problems for
someone who claims that such behavior only occurs in fully modern
humans. (Determining what behavior qualifies is also problematic,
but for the present argument the date is the issue.)
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted
Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at
Droitgate Spa
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