The notion of ‘ontology’ does not loom large in the science
of geology. In part, this is
because geology is wedded to geological history,
which, as in the case of its human counterpart, does not self-dissect neatly
into freestanding classes of elements.
Further, even synchronically,
the various rocks and minerals don’t form anything like the brilliantly
ordered structure of the Periodic Chart of the Elements.
Still, as a finger-exercise, joining our “The Ontology of …" hit-parade --
http://worldofdrjustice.blogspot.com/2011/10/ontology-of-physics.html
http://worldofdrjustice.blogspot.com/2011/01/ontologia-numerorum.html
-- we try our hand at it here.
Consider orology: study of the structure and genesis of
mountains.
Notoriously (this is a chestnut within semantics), the
notion ‘mountain’ is vague in two quite different ways: (1) what counts as a single
mountain, rather than a blip in a ridge;
(2) what counts as a mountain at all, rather than a hill or ‘eminence’.
Those perplexities concern only the most superficial aspect
of a mountain, its size. More
significant in terms of geology as a science
(as opposed to landscape painting) are the structure and placement of
mountains, both of which are strongly effected by their orogeny -- volcanic
versus non-volcanic mountains are quite different critters; it is only an accident that we use the
same word for each.
Thus, this scoffing, from our preëminent bard of geology:
We came to an escarpment known as White Mountain. .. In no tectonic sense was this a true mountain -- a folded-and-faulted, volcanic, or overthrust
mountain. This was just a
Catskill, a Pocono, a water-sliced segment of layered flat rock, a geological
piece of cake.
-- John McPhee, Annals of the
Former World (1998), p. 410
Similarly, the idea of a ‘continent’ : (1) what counts as a single continent (is Eurasia one or
two?) (2) what counts as a continent
at all, rather than an island or atoll.
Thus, Australia, the “Pluto” of the continental system. (Or, more subtley and structurally,
Cyprus.)
Only with tectonics
did the notion of a continent
become crisp and interesting.
It was realized later that the true
edges of the continents lay not
where the shorelines happened to be, but at the edges of the continental slabs
themselves, below sea level.
-- Richard Fortey, Earth
(2004), p. 142
The tectonic criteria in hand, it was then concluded that,
200 years ago, theory required a meta-entity, Gondwana, a supercontinent,
consisting of several that are separate today. -- At the opposite end of the spectrum John McPhee at one
point refers (perhaps humorously) to a “micro-continent”, which would be a
reductio ad absurdum for the notion of “continent” as an ontological peg-point
in geology.
More fundamental than continents are the tectonic plates, which are dynamically
better defined. A somewhat
similar concept that has risen into prominence in later days is the terrane. Here, too, in
is possible in practice to proliferate entities beyond necessity, a practical
about which some geologists are
… Homicidal in their sarcasm. … In the geology of such [ontologically
profligate] people, it is said, a microterrane
is a field area, a nanoterrane is an
outcrop, a picoterrane is a hand
specimen, and a femtoterrane is a thin section.
-- John McPhee, Annals of the
Former World (1998), p. 511
“Femtoterrane” -- that’s funny.
~
A further problem with plates is that they are of disputed
reality in the pre-Cambrian times prior to the Proterozoic -- the Archaean. A unique continuity obtains at the
juncture of those eons:
“The Archean-Proterozoic transition
is a real threshold in the behavior of earth. .. If you want to define plate tectonis strictly on the modern model, then you
have to coin another term for the Archean tectonics.”
-- John McPhee, Annals of the
Former World (1998), p. 633-4
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