Geology Reference
In-Depth Information
shared with a neighboring tetrahedron. So it was in the beginning, and is
now, and ever shall be so long as nature's laws prevail. Cambrian quartz is no
different from Pleistocene quartz.
But life is complex enough to change through a series of unrepeated states.
Today we attribute this irreversible sequence to the workings of evolution,
but the fact of uniqueness may stand prior to any theory invoked to resolve it.
The fossil criterion became the Rosetta stone for the stratigraphic research
program, but few early consumers accepted evolution as the reason behind
distinctive temporal stages of the fossil record. In Lyell's time, the fact of
temporal distinction stood as an unexplained but crucial tool. Lyell himself
had always professed agnosticism about the reasons, stating that he simply
did not know whether new species arose by God's direct will, or by the
operation of unknown secondary causes—though he did profess confidence
that they arose in perfect balance with their environments.
In Lyell's time, the problem of unresolved Tertiary stratigraphy centered
upon a proper use of fossils to "zone" strata—that is, to establish a worldwide
sequence of temporally ordered stages within this long and previously
undivided segment of the earth's history. In 1830, most stratigraphers were
progressionists. They believed that life had improved throughout the Tertiary
and that, as a rough guide at least, we might judge the relative age of Tertiary
strata by the level of development displayed in their fossils. All
paleontologists understood that progress was neither sufficiently linear nor
unambiguous enough to employ as an actual measuring rod. In practice, a
progressionist might use similarity to living forms, rather than some
unattainable measure of relative perfection in biomechanical design.
Moreover, he would search for a series of guide fossils—easily identifiable
creatures of short and distinct geological range—to zone the Tertiary. And he
would focus more upon their uniqueness and restriction to a small stretch of
time than upon their supposed levels of relative complexity. Still, however
far practice diverged from theory, a commitment to progressionism still
channeled the actual work of stratigraphy into a search for temporal
sequences of guide fossils arrayed as a ladder of improvement.
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