Given that both Glenn and Bill did not take my comments as I intended, I
need to clarify them.
If evolutionary changes are spread out in time, then ordinary slow
sedimentation will produce the observed patterns of faunal succession in
the geologic column. Only if the faunal changes were rapid enough to fit a
young-earth scenario does rapid sedimentation become necessary. The
scenario then collides into Glenn's admonitions about sinking rates, with
the caveat of possible speeding up due to being incorporated into larger
lumps such as fecal pellets (not enough to help for a one-year flood, but
enough to explain how come they do not all dissolve before reaching the
bottom).
Modern sedimentation rates can be measured. Areas such as the open ocean
that are far from sources of eroded sediment (mostly rivers) or high levels
of biogenic production (shallow water) have very low sedimentation rates.
If rapid changes in coccolith morphology were to occur today, with
different kinds replacing each other within a few years to decades or
centuries, the sedimentary record would show an increase in variation, not
a series of forms replacing each other, becuase each new kind would get
mixed in with the old before it was buried. If this kept up, eventually
there would be some shifts in the mix as all of the oldest forms finally
got buried. We also have samples collected over 100 years ago, so we know
that the coccoliths are not changing form that rapidly.
Vardiman proposed an exponential decrease of sedimentation rates from the
end of Flood (tentatively equated with the K/T) to the present, but this is
based on no evidence, just that exponential patterns are common. It also
requires ridiculously high rates of sedimentation immediately after the
Flood, if not much more recently (try fitting an exponential curve for the
Cenozoic to the post-mid Pliocene of Galveston Island, Texas) and ignores
all the unconformities, diastems, condensed sections, expanded sections,
stratigraphic markers, and other evidence for non-constant variation in
sedimentation rate.
Depending on the degree of bioturbation relative to the sedimentation rate,
the size of the layers preserved will vary. Sediment anoxia or other
stressful conditions (intertidal) can also limit bioturbation. There are
a variety of measures for the level of bioturbation in ancient systems,
which ranges from very high to very low.
>Document a case of _evolution_-induced, irreversible morphological change
>among forams, nannoplankton or diatoms. Prove that the change was slow
>and gradual rather than rapid.
Evolution doesn't exactly induce, but rather the change is evolution.
There are a variety of morphological changes that take place through
intermediate forms to new forms that then persist for a while before
evolving into new forms, even though the environment has not changed. For
example, perhaps as few as two or three species of planktonic foram
survived the K/T event. In the Paleocene, after the layers containing just
the survivors and reworked dead forams, modified versions of these forms
appear, showing both obvious connection to the survivor species and
foreshadowing of major later lineages, which they later evolve into. The
changes are rapid by geologic timescales, but are slow enough to show up in
the fossil record, even with bioturbation, and are separated by long
intervals without change.
David C.