Download Y2K, DEEP TIME, AND THEORY CHOICE IN GEOLOGY

Y2K, DEEP TIME, AND THEORY CHOICE IN
GEOLOGY
concept, and only dimly as a reality. It
was the Geologists who, through their
attempts to understand the formation of
earth's landforms, brought the concept of
deep time into science.
MILLENNIUM MADNESS
Madness is rare in individuals, but in
groups, parties, nations, and ages, it is
the rule.
-Friedrich Nietzsche
I recall the hoopla that surrounded
the transition from 1999 to 2000, the
dawn of the 3rd millennium.
I
considered the fuss important only
because some pieces of equipment might
have stopped working. Also, we were
inconvenienced by the temporary loss of
a few services.
Actually, the millennium, a thousand
year period, is an accident of evolution
(we have adopted a base ten number
system because we have ten fingers), an
accident of cosmology (a year has the
particular period or length of time
because of the earth’s distance from the
sun), an accident of biology (we have a
life span that approaches 100 years, so
ten times that length is just beyond the
understanding of any one person but
within the understanding of a culture),
and an accident of history (numbering of
the current era began at an arbitrary year
1). Thus, the particular year of 2000 (or
2001 if you are a purist) becomes trivial
by almost any way of reckoning it.
Measured relative to the age of the
earth, a 1000-year period is like a drop
in the bucket. However, a serious
consideration of the earth’s age requires
an understanding of the concept of Deep
Time. That is, thinking of time in
millions and billions of years. These
periods of time are so much out of a
human’s everyday, lifetime or cultural
experience that we can understand them
only rationally. That is, we understand
"billion" first as a word, secondly as a
BY WATER
Werner had great antipathy to the
mechanical labor of writing, and he
could never be persuaded to pen more
than a few brief memoirs.
-Sir Charles Lyell
Before the 18th century there was
little
speculation
about
the
transformation of the earth's surface.
Some troubling things like marine fossils
on mountaintops appeared in the
discussion but were explained away as
failed creations of life or evidence of
The Genesis Flood.
That a single
catastrophe like The Flood or series of
flooding catastrophes could explain the
earth's landforms gave way to a theory
that assumed the earth originally was
covered by water. Gradually, the waters
receded, and as they did, landforms of
the earth appeared above the waves and
took shape. Adherents to this theoretical
view were called the Neptunists after the
classical god of the sea. An important
aspect of this view is that it could
explain the earth in the 5-10 thousandyear period assumed to have occurred
since The Creation.
Neptunists explained crystalline
rocks like granite and many other
minerals as having grown as crystals in
the waters of a younger earth. While
covered with water, suspended rocks,
sands, down to very fine particles
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differentially settled out and made the
layers of sedimentary rocks.
German geologist, Abraham Werner
(1750-1815), one of the principle
Neptunist theorists supposed that the
earth's landforms came about by the
processes
of
precipitation
and
crystallization from a primordial sea.
Therefore, older layers lay beneath
younger layers. Werner even explained
the occurrence of volcanoes as relatively
new structures that were formed by
subterranean coal fires.
eroded the rocks of volcanic origin to
produce sedimentary rocks.
Hutton assumed that the natural
processes at work on the earth now are
the same ones that shaped the surface of
the earth from the time it was a molten
ball.
This Uniformitarian Principle
required immense amounts of time to
wear
down
mountains,
produce
sedimentary rocks that then also erode
away, etc.
This principle became
Hutton's major contribution to the
sciences, and developed into the
cornerstone of Geology.
Hutton's vision was quite grand. He
saw the earth as a great heat engine with
volcanoes producing the raw materials
for the renewal of the surface landforms.
The goal of this cycle of rocks and
erosion was the production of soil.
BY FIRE 1
With no vestige of a beginning and no
prospect of an end.
-James Hutton
An alternative theory said that
volcanoes were responsible for the
origin of the earth's landforms. John
Ray (1627-1705), a British scientist,
believed that mountains were formed by
volcanic action. Also, the layers of
sedimentary rock recorded a series of
volcanic eruptions. This view required
much longer periods of time with the
same mechanism repeating again and
again. During the 18th century, the
followers of Ray (called Vulcanists or
Plutonists) explained the volcanic origin
of continents, ocean basins, as well as
mountains.
James Hutton (1726-1797), a
contemporary of Abraham Werner,
expanded on the Vulcanist theory.
Through observations that he made in
Edinburgh, Scotland and during his
travels, he began to speculate that that
the center of the earth is molten. Rocks
like granite and basalt came from that
molten center via volcanoes. Water then
MODERN GEOLOGY IS BORN
When we compare the result of
observations in the last thirty years with
those of the three preceding centuries,
we cannot but look forward with the
most sanguine expectations to the degree
of excellence to which geology may be
carried.
-Sir Charles Lyell
Hutton's vision was set down in a
rambling 1000 page book called the
Theory of the Earth in 1795. It was
poorly written and his explanations were
so ambiguous that arguments arose
almost immediately as to what his
conclusions really were.
Sir Charles Lyell, a fellow Scot with
an interest in Geology, took parts of the
Neptunist
theory
that
explained
sedimentation,
the
formation
of
sedimentary rocks, and the relative ages
of sedimentary rock layers. Also, he
retained the view that the earth had an
origin and a history.
1
Please consult Geology Through Lyell’s Eyes
for an expansion on the contributions of Werner,
Hutton, and Lyell.
2
Lyell kept much of the Huttonian
Vulcanist theory and expanded on the
Uniformitarian Principle. He eliminated
Hutton's view of an eternal earth, but
retained the requirement of long periods
of time. In short, his theory proposed
that the earth's surface became more
uneven by volcanic or igneous processes
and became more even by erosion or
aqueous processes.
Lyell's Principles of Geology
(Volume 1 was first published in 1830)
was well written and successfully
integrated portions of the Vulcanist and
Neptunist theories with the central theme
of
gradualism,
based
on
the
Uniformitarian Principle.
The book
grew to three volumes and went through
12 editions. It had a major impact on
geologists and naturalists of the mid-19th
century, including a young naturalist
named Charles Darwin on his voyage of
discovery.
The vestiges of the Neptunist Theory
became manifest in a young earth view
in which the earth was shaped by a series
of catastrophes. Lyell would not budge
on his requirement of a gradual,
uniformitarian process of landform
creation. By the end of the 19th century,
Gradualism had won out in the
community
of
Geologists
and
catastrophes were no longer allowed as
explanations.
century. Descriptions of minerals and
the physical processes involved in the
formation of rock layers seemed to be
pretty well known. Strata had been
classified into broad ages and correlated
across the planet 2.
All could be
explained within a gradualist theory.
Geologists theorized that mountains,
continents and ocean basins formed on
the earth as a consequence of gradual
cooling from a molten ball. As it cooled,
it shrank slightly, thereby wrinkling the
outer crust. It was in consideration of
the cooling rate that a crisis arose in the
sciences when physicists like William
Thompson, Lord Kelvin chose to tackle
the problem of the age of the earth using
the
principle
of
uniformitarian
gradualism, the fundamental principle of
geology itself. If the earth cooled from a
molten ball to an earth with a molten
interior and a crust of only 50 miles
thick, then the earth could be no more
than 100 million years old. Indeed,
some of Kelvin's calculations seemed to
say that the earth was as young as 24
million years. This new young earth
theory was based on a physical
calculation that was confirmed by other
physicists.
Not until the discovery of
radioactivity and the realization that the
interior of the earth contains small
amounts of radioactive elements did a
source of heat appear to counter Kelvin's
assertion. At the time, though, his
argument had been so compelling that
some geologists had begun to
accommodate theory to agree with the
new dates. They assumed that the
Uniformitarian Principle must be
modified to say that geological activity
was much more intense during the early
earth and then it slowed down in more
recent times.
A PHYSICIST'S CHALLENGE
His impulse was to correlate phenomena
and arrive at the principle underlying
them, and this gave him a certain
impatience with branches of science that
were still in the observational stage…
-A Student of Lord Kelvin
Traditional
disciplines
within
geology such as minerology and
stratigraphy blossomed during the 19th
2
3
I have expanded on this in Reading the Earth.
less dense that basalt, so it appeared that
the continents were higher because they
"floated" on the denser mantle and ocean
basin material.
Alfred
Wegener
(1880-1930)
embraced the concept of floating
continents at the turn of the 20th century.
Although he had received a doctorate in
astronomy in 1905, Wegener quickly
turned his attention to the weather and
made important contributions to the
study of meteorology. In the mean time,
he became intrigued by the remarkable
fit between the continents of South
America and Africa. Although he was
not the first to do so, Wegener gave the
connection his full attention in 1914 as
he lay in a hospital recovering from
wounds suffered during the First World
War.
As he convalesced, Wegener
began to collect evidence from
stratigraphy and paleontology.
He
discovered that there are places that
seem geologically continuous from one
continent to another as if they were just
torn apart. Also, the two continents
shared particular plant and animal fossils
that could not have made the transit
across the Atlantic Ocean.
Wegener collected enough evidence
to convince him that all of the earth's
continents had once been connected into
a supercontinent that he called Pangaea.
He published his ideas in 1915 in The
Origin of Continents and Oceans (see
Figure 5-9). In Wegner's view, the
continents then broke apart and drifted to
their present positions as they floated or
slid over the plastic mantle. He looked
in vain for a force sufficient to overcome
the enormous forces of friction. He
speculated that lunar tidal forces or the
centrifugal force exerted by the spinning
earth would be enough to move the
continents like great ships over the
earth's surface.
The community of
The discovery of radiation and the
understanding of the half-lives of the
products of radioactive decay led to the
opposite problem. This indicated that
the earth was immensely old, on the
order of billions of years. Also, the
cooling rate must have been so slow that
ocean basins and mountains could not be
explained that way.
It was an
intellectual Pyrrhic victory.
SLIDING CONTINENTS
It is probable that the complete solution
to the problem of the forces will be a
long time coming. The Newton of drift
theory has not yet appeared.
-Alfred Wegener
The view at the turn of the 20th
Century was that the earth was very old.
Its continents and ocean basins had been
altered by fluctuations in water level,
mountain formation, and erosion. How
were mountains formed? Volcanoes
were easier to understand than the large
mountain ranges of folded sedimentary
rock.
What could have generated
enough force to cause large expanses of
sedimentary rock to buckle and rise?
Some postulated that rolling currents
developed in the mantle, a hot zone
between the molten core and the solid
crust. As the mantle moved, parts of
crust wrinkled above them. This served
as an explanation for why there were
mountains of very different ages and
how mountains could have been formed
in the absence of a cooling, shrinking
earth.
Also, it was noted that although
continents seem to be made of recycled
materials, the core of the continents was
made of granite, a kind of igneous rock.
The ocean basins, on the other hand,
were made of basalt, another kind of
igneous rock. Curiously, the granite was
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geologists did not accept Wegener's
ideas. His evidence was viewed as
circumstantial and his explanations for
the movement absurd. What is more, he
was an outsider, a meteorologist
meddling in geology.
Wegener spent his professional life
working on meteorology and defending
his theory of Continental Drift to no
avail. He died during an expedition to
Greenland at age 50, and his theory of
Continental Drift was relegated to an
interesting footnote in the history of
geology.
to light in sea floor research. First,
examination of the sediments of the floor
of the Atlantic Ocean showed that they
were quite young and thin. Static Earth
Theory required that the ocean basins
had accumulated sediment continuously
for the earth's long history. However,
collected sediments were thicker and
older nearer the continental margins and
younger toward the middle of the
Atlantic.
The center of the Atlantic Ocean had
a ridge that ran the full length (north to
south) and was equidistant from
continents to the east and west. Hess
and others recognized that the ridges
were volcanic in origin and were sites of
upwelling and spreading of material
from the mantle. Hess suggested that the
ridge overlay a rising convection current
that was fueled by heat from radioactive
decay. This explanation came together
with evidence that ocean crust returned
to the mantle at ocean trenches where
the spreading seafloor forced oceanic
crust to dive beneath the less dense
continental crust.
Furthermore, the
subducted crustal material must melt
when it dives into the mantle and rise
again to form volcanoes.
That
continental volcanoes were associated
with these areas of subduction confirmed
the theory.
In 1962, Harry Hess put all of this
together in his theory of Sea Floor
Spreading (see Figure 5-10). In this
view, the continents did not plow
through sea floor, but rode on them as
passengers. At last the obstacle to
Wegener's Continental drift was
overcome. A plausible mechanism for
change had been offered. Hess became
Wegener's much-needed Newton of drift
theory.
FIGURE 5-9. Alfred Wegener's
illustration of Pangaea from The Origin
of Continents and Oceans.
NEWTON OF DRIFT THEORY
One of the truly remarkable earth
scientists of this century.
-National Academy of Sciences Memoir
Harry Hess (1906-1969) earned a
Ph.D. from Princeton in 1932, two years
after the death of Wegener. During
World War II, Hess served in the U.S.
Navy, ultimately rising to the rank of
Rear Admiral. He developed a system to
track German submarines and made
thousands of depth soundings across the
Pacific Ocean.
Following this
experience he continued his interest in
ocean basins by forming and directing
the Princeton Caribbean Research
Project.
During this time, Hess considered
some lines of evidence that were coming
5
began to crystallize. As the waters
receded, more layers formed so that
younger layers overlay older layers.
This theory did not require a very old
earth, but it did require a place for all of
that water to go.
In the Vulcanist Theory, landforms
were created gradually by successive
volcanic events. Thus, long periods of
time were necessary. Indeed, in the
Vulcanist theory of Hutton, time became
cyclic, without a beginning or an end,
operating on
the
Uniformitarian
Principle.
Charles Lyell then took parts of the
Neptunist and Vulcanist Theories and
wove them into a new way of explaining
the earth. He kept the stratigraphy and
minerology of the Neptunists and
adopted the uniformitarian gradulaism of
Hutton with the concept of an earth with
a molten center. In this view of deep
time, the earth was very old, but it did
have a beginning. Lyell's theory did
survive challenges by the catastrophists
and physicists who said that the earth
had to be much younger.
Wegener's
Continental Drift theory never entered
the mainstream of the science of
geology. It was interesting, but offered
no mechanism to explain how the
continents could move. Then following
Hess' theory of Sea Floor Spreading,
Wegener's Continental Drift transformed
into Plate Tectonics, the central
paradigm of geology.
Still, Plate Tectonics is not
completely new. It has vestiges of
Neptunism, Vulcanism, Static Earth, and
Continental Drift. Above all, it is a
fruitful theory allowing our explanations
of landforms to go beyond the bounds of
this earth and through immense periods
of time.
FIGURE 5-10. A diagram of sea floor
spreading.
Sea Floor Spreading is the
fundamental concept on which the
Theory of Plate Tectonics is built. In
this theory, the earth's surface is divided
into a number of crustal plates like a
cracked egg (see Figure 5-11). The
plates move by spreading or slipping
past each other. Sometimes they collide
(the Indian and Eurasian Plates), and
sometimes they slip beneath or subduct
beneath another plate (the Nazca and
South American Plates). This is a
beautiful theory in that all landforms on
the earth can be explained by these
actions accompanied by erosion.
By 1967, the theory was defined and
began to be tested. Now, the theory is
useful in understanding landforms on Io,
Venus, Europa and other planetary
bodies. More direct measurements of
the movement can now be made by
satellite. The Atlantic Ocean spreads at
about 5cm per year. Other plates move
at different rates. The surface of the
earth is anything but static.
THEORY CHOICE
What better criterion could there be than
the decision of the scientific group? Thomas Kuhn
Now return to the various theories
that I have explored. The Neptunists
said that a primary sea had covered the
earth. From that sea, rocks and minerals
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FIGURE 5-11. Map of the major plates and their boundaries. Image from USGS at:
http://easternweb.er.usgs.gov/eastern/plates.html
Thus, the concept of deep time
These things were far more important to
me than a celebration of insignificance.
became part of Geology, and allowed for
-2000; revised 2004
the development of subtle, more general
References:
theories to explain the nature of the
Bowler, Peter. 1992. The Fontana History of the
earth. The fruitfulness of deep time as a
Environmental Sciences. Fontana Press.
principle caused it to weave itself into all
London.
disciplines of science. Thus, my rational
Gould, Stephen. 1987. Time's Arrow, Time's
understanding of deep time tempered my
Cycle.
Harvard
University
Press.
Cambridge, Mass.
enthusiasm for celebrating the new
Gould, Stephen. 1997. Questioning the
millennium.
Millenium. Harmony Books. New York.
Kuhn, Thomas. 1977.
Objectivity, Value
Judgement, and Theory Choice. In: Curd &
Cover, eds. 1998. The Philosophy of
Science, The Central Issues. W.W. Norton
& Co., Inc. New York. pp 102-118.
Lyell, Charles. 1990 (originally published 183033). Principles of Geology With a new
Introduction by Martin J. S. Rudwick. Vols.
1-2. The University of Chicago Press.
Chicago.
Schuchert, Charles. 1928. The Hypothesis of
Continental Displacement. Annual Report of
the Board of Regents of the Smithsonian
Institution. US Government Printing Office.
Washington. pp 249-282.
Trefil, James and Robert Hazen. 1998. The
Sciences, An Integrated Approach. John
Wiley and Sons, Inc. New York.
Wegener, Alfred. 1966 (originally 1915). The
Origin of the Continents and Oceans.
Translated by John Biram. Dover
Publications, Inc. New York.
Y2K
Someday we’ll all look back on this,
laugh nervously, and change the subject.
-A Bumper Sticker
The year 2000 came and went, and
much ado was made of that "landmark"
time. I was so tired of hearing about it
that I welcomed the next week when our
attention-deficit culture turned its eyes to
something else. After all, during the
past 2000 years the Atlantic widened by
only 100 meters. The whole Atlantic
Ocean began to form only 140 million
years ago, a mere 1/30th of the age of the
earth. On New Year's 2000, I sang and
danced. I celebrated friendships and life.
7
Questions to Think About
1. What were the contributions of Werner, Hutton, and Lyell in the development of modern
geology?
2. How did Lord Kelvin and other physicists present a significant challenge to one of the
fundamental principles of geology?
3. How was that challenge resolved?
4. What was Alfred Wegener’s theory of the earth? Why was it generally not accepted by
geologists?
5. How could Harry Hess be described as The Newton of Drift Theory?
6. What is the theory of seafloor spreading? How does it help to explain the surface
features of the earth?
7. How do continental volcanoes fit into the theory?
8. How is Plate Tectonics different from Continental Drift?
9. What do you think of the following comment by Thomas Kuhn: What better criterion
could there be than the decision of the scientific group? To what was he referring?
10. Consider the history of geology. Did new theories ever really supplant those that
preceded them? How does Plate Tectonics carry the vestiges of the Neptunists,
Vulcanists, Hutton-Lyell, and Wegener.
8