| 64 This View of Life |
Natural History 5/97 |
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hemisphere and subtracting from
the other (for the entire block had previously resided in one hemisphere alone).
Leonardo includes a striking illustration of this process in the Codex Leicester,
showing a fallen block as a large arch nicely draped about the center of the world.
In describing this internal mechanism in the Codex Leicester, Leonardo
explicitly cites the rising of fossiliferous strata as a consequence:
The fact of the summits of the mountains projecting so far above the watery
sphere may be due to the fact that a very large space of the earth which was filled
with water, that is the immense cavern, must have fallen in a considerable distance
from its vault toward the center of the world, finding itself pierced by the course
of the springs, which continually wear away the spot through which they pass.
. . . Now this great mass has the power of falling. . . . It balances itself with
equal opposing weights round the center of the world, and lightens the earth from
which it is divided; and it [the lightened earth] removed itself immediately from
the center of the world and rose to the height, for so one sees the layers of
the rocks [with their fossils], formed by the changes which the water has undergone,
at the summits of the high mountains. The exterior
method of lightening by erosion can enhance this process once the mountains rise.
Rivers will now erode the sides of the mountains and carry sediment away to the
oceans. Some sediment will flow to the opposite hemisphere, thus further increasing
the imbalance of weight, and causing the mountains to rise still higher as a consequence.
And now these beds are of so great a height that they have become hills
or lofty mountains, and the rivers which wear away the sides of these mountains
lay bare the strata of the shells, and so the light surface of the earth is continually
raised, and the antipodes [the opposite side of the earth] draw nearer to the
center of the earth, and the ancient beds of the sea become chains of mountains.
T hus,
and finally, we grasp the central importance of Leonardo's paleontological observations
in the Codex Leicester. He featured this subject in order to validate the
most cherished centerpiece of his premodern worldview--the venerable argument,urged throughout classical and medieval times, for considering the earth
as a living, self-sustaining "organism," a macrocosm working by the
same principles and mechanisms as the microcosm of the human body. Leonardo required,
above all, a general device to make the heavy elements, earth and water, move
upward against their natural inclination--so that the earth could sustain
itself, like a living body, by constantly cycling all its elements, rather than
reaching inert stability with heavy elements in permanent layers below lighter
elements. Leonardo failed to find such a mechanism for the chief subject
of the Codex Leicester: water--and this lack of resolution caused him
great frustration. But he succeeded for the even heavier element of earth. He
extended a mechanism pro-posed by Scholastic philosophers for causing the lighter
hemisphere of an unhomogeneous planet to rise. He proposed both internal and external
erosion by water as devices that could lighten a hemisphere--but he needed
observational evidence that land did, in fact, rise. His crowning jewel of confirmation
lay in a well-known phenomenon that had provoked intense debate ever since the
days of classical Greek science--fossils of marine organisms in strata on
high mountains. Leonardo also needed to assert that the rising of strata
with fossils must represent a general and repeatable feature of the earth's behavior,
not an odd or anomalous event. Thus, he had to refute the two explanations for
fossils most common in his time--for Noah's flood could only be viewed as
a strange and singular phenomenon, and if all fossils derive from this event,
then paleontology illustrates no general mechanism for the rising of land. And
if fossils grow as objects of the mineral kingdom within rocks, then the mountains
may always have stood high, and we can derive no evidence for any uplift at all.
Thus, Leonardo made his superb observations on fossils to validate his lovely,
but ever so antiquated, view of a causally meaningful and precise unity between
the human body as a microcosm and the earth as a macrocosm. Leonardo, the truly
brilliant observer, was no spaceman, but a citizen of his own instructive and
fascinating time. I like to contemplate Leonardo, this complex man of peace,
of gentleness, of art, of scholarship; this military engineer who designed (but
generally did not build) ingenious instruments of war, but who would not reveal
his ideas for a sub-marine, as stated in the Codex Leicester:
This I do not publish or divulge on account of the evil nature of men who
would practice assassinations at the bottom of the seas, by breaking the ships
in their lowest parts and sinking them together with the crews who are in them. And
I like to compare his views on the mechanism for raising mountains from the sea
(and exposing fossils for collectors) with our most celebrated literary image
on the same subject--Isaiah's prophesy that "every valley shall be exalted."
I also recall the peace that shall reign on Isaiah's mountain (festooned, no doubt,
with fossils), where a scholar might study the raising of earth to his heart's
content and not need to provide his warlike patron with plans for the raising
of sieges or the razing of enemy cities--Isaiah's summit. where "the
wolf also shall dwell with the lamb, and the leopard shall lie down with the kid.
. . . They shall not hurt nor destroy in all my holy mountain."Stephen
Jay Gould teaches biology, geology, and the history of science at Harvard University.
He is also Frederick P. Rose Honorary Curator in Invertebrates at the American
Museum of Natural History. |