KNO WLEDGE OF THE PAST
1. A skeptical argument:
A. The nature of knowledge.
What we know is normally expressed in terms of declarative
sentences, often set in a “that” clause:
I know (that) Jean Chretien is Prime Minister.
I know (that) the room we’re in is TH 103.
Tony Blair knows (that) his government exaggerated the evidence of
Iraqi WMDs.
The “that” clause indicates what the subject of the sentence knows
(sometimes we say it specifies the content of what’s known).
Knowledge must meet three conditions:
i.
Belief: To know something, you must believe it—if you don’t
believe these things, you don’t know them. (Sometimes, when
the evidence is finally in, someone will say “I just knew it,”
when in fact they weren’t at all sure in advance. But this is not
literally true—they didn’t know (perhaps they suspected, or
feared, or hoped; but none of these states of mind constitutes
knowledge).
ii.
Truth: We cannot know what isn’t true. We can believe things
that are false, of course, and be very confident about them, too
(and sometimes people express such confidence by saying that
they know), but in the end, if it isn’t true, we don’t know it, no
matter how confident we are about it.
iii.
Justification: We cannot know something just by guessing at
the truth and getting lucky. We need to have good (sufficient)
reason for our beliefs before they can count as knowledge.
These three conditions are required, but not sufficient for knowledge, as
a very interesting class of examples illustrates. But our argument
doesn’t need a definition of knowledge—all it requires is some details
about the justification condition.
Justification, it is often said, cannot be circular. That is, if I know that p
(for some declarative sentence p), then I need a justification for p; last
time we described this justification as some further declarative
sentences that I know and that constitute(s) a sufficient justification for
p. Call these sentences q, q',… Then my justification for p is circular if
my justification for one or more of q, q',… depends on being justified in
believing p.
The problem is obvious—if my justification of p depends on my being
justified in believing q, and my justification of q depends on my being
justified in believing q, then both justifications are in question. I
haven’t really justified either yet.
B. Evidence about the past.
There are all kinds of things we claim to know about the past; if
we’re right about these claims, there must be some way of justifying
them.
Consider a few things I know about the past:
I had a bagel for breakfast this morning.
John F. Kennedy was assassinated in 1963.
Aristotle taught Alexander the Great.
The Sumerians developed the cuneiform system of writing.
Glaciers spread across northern Europe and North America within
the last 20,000 years.
Trilobites were arthropods that thrived during the Paleozoic era.
How do I justify these claims? The answers are obvious at first—I
remember eating the bagel, and I remember JFK’s assassination and
that it took place during the year I was in grade 2. I’ve read about
Aristotle and his place in the Macedonian court, which is well-known
to ancient history types and well documented. Similarly, I’ve read
about cuneiform writing (and its roots in simple accounting
techniques). I’ve both directly seen evidence of glaciation
(striations, polished pavements, kettle lakes, moraines, drumlins,
etc.) and read a lot about the evidence, its history, and the
conclusions geologists have drawn from it. Finally, I’ve seen fossils
of trilobites and read about them as well; their place in the geological
column is secure, and their status as arthropods is likewise firmly
established.
Is there anything in common amongst these justifications? Here’s
something—they all depend on assumptions about processes linking
the present situation to some fact(s) about the past:
When I talk about what I remember, I assume that there is some
process connecting my present memory to the facts I am
remembering. Something happened (I ate a bagel, JFK was
assassinated) and I was or became aware of it (my senses detected it,
in the first case; I heard it over the radio in the second), and that
awareness left a persistent trace (a memory) that remains in me
today, a trace that somehow encodes information about what
happened that I am able to understand.
When I talk about documented historical events, different processes
are involved, but the same pattern occurs: a present trace encodes
information about a past event because of a process linking that
event (or certain facts about it) to the present existence and features
of the trace.
And the same goes for geological evidence and the conclusions we
draw from it.
C. The Skeptical Argument.
Now we’re ready to see the problem. Processes take place over time—
any knowledge we have about processes is knowledge about the past.
So to justify my knowledge claims about the past, I need more than just
knowledge of the present traces. I also need knowledge of the processes
that have produced them—that is, I need knowledge of the past to
justify knowledge claims about the past. We are stuck in a circle—to
justify a claim about the past, we must already know something about
the past. So if our knowledge about the past must be founded
exclusively on knowledge about the present, we can’t have any
knowledge of the past at all.
This leads directly to a kind of radical skepticism about the past: No
matter what the present facts we now observe are, we cannot justify
inferring anything about what has happened before now.
D. Responding to skeptics.
This kind of circle is a familiar phenomenon. It goes back more than
2000 years, to Diodorus, who proposed an argument called “the wheel”.
For Diodorus, the puzzle was about knowledge of truth. There are
certain sentences that we take to be true. If someone asks us how we
can tell that they are true, we need to provide some criterion that we use
to separate truths from falsehoods. But if they then ask how we know
that this is a good criterion, we are faced with a difficult choice:
Either there is some higher-order (meta-) criterion that this criterion
satisfies (and they will surely ask how we know that criterion is a good
one), or the criterion is a good one because it reliably picks out
sentences we know are true (and they will surely point out that we
invoked the criterion in the first place to defend our commitment to the
sentences, so surely it’s cheating if we now, circularly, appeal to the
sentences to defend the criterion).
Here is a diagnosis of the problem: If we assume that we’re starting
from zero, we’re in trouble. And so we should be. If we don’t have any
idea of what’s true, of what it takes to be true or how to tell if a sentence
is true, then we can’t “bootstrap” our way to a defensible account. You
can’t find something unless you have some idea of how to tell when
you’ve found it! But if we start with a reasonable (if partial, flawed and
fallible) account of some things that are true and some ways of deciding
what’s true and what isn’t, then we’ve got something we can build on.
The same goes for knowledge of the past. If we start with no idea of
what processes have taken place in the past, then nothing we observe
now can justify conclusions about the past. But if we start with some
ideas about what processes have produced various features of the world
around us, and compare and test these against the “traces” we find in the
world around us, then we can evaluate our claims about the past.
The evaluation turns on the coherence and vindication of the accounts
we give. Coherence requires a nice fit between all the various aspects
of the story we tell—what we observe about present traces and what we
say about the processes they are traces of must fit together; the traces
must be the sort of traces (and arranged in the sorts of ways) we would
expect the processes to produce. (This is the virtue that drives
theoretical work, in which we try to invent hypotheses that will explain
the evidence.) Vindication requires a little bit more—to vindicate our
views, we must apply them successfully—for instance, by making
predictions about features of the traces we expect to observe, given our
present commitments about processes, and then observe the predicted
features. (This is the virtue that drives empirical work, in which we test
the hypotheses theorists come up with.)
Processes:
Let’s list some of the main processes that are central to geological
thinking about the earth. As we read through the history, we’ll see
many examples of models of these processes (and others, which have
fallen by the wayside in geological thinking), together with arguments
about how well or poorly these models fit the evidence (i.e. traces) they
are meant to account for:
Erosion (See especially Hutton, Lyell)
Sedimentation/Deposition (see Steno)
Formation of rocks & minerals (see Werner, von Buch, Desmarest,
Hutton)
Fossilization (see Steno, Leonardo,
Volcanic activity (see Guettard, Desmarest, …)
Orogeny (mountain building) (see de Beaumont, Agassiz, Darwin)
Formation of valleys (see Scrope, Cuvier (?), de Beaumont, …)
Glaciation (see Peraudin, Venetz, Charpentier, Agassiz, et al.)
…
Many authors have drawn lines between what are called the historical
sciences and the lab, or theoretical sciences. The historical sciences
include geology together with paleontology and the application of
evolution to account for the history of life, while the lab sciences
include physics and chemistry. Creationists have emphasized this
distinction, arguing that there is a greater degree of uncertainty about
the results of the historical sciences because (at least in most cases)
“there are no witnesses to the events they describe,” while the theories
of the lab sciences are directly tested (even “proven”) by measurements
we can witness today.
But this is a serious mistake, as a little thought will tell you. For
instance, we have a powerful theory of electromagnetic radiation,
embodied in Maxwell’s equations. This theory is a paradigmatic
example of a lab science. We have tested this theory over and over
again, and (aside from the subtleties of quantum mechanics, which lead
to important modifications for small-scale processes) it is as wellconfirmed and reliable as any theory we have. One important result of
this theory is that the speed of light turns out to be a fixed quantity,
related to the electromagnetic properties of empty space. Similarly, the
constancy of spontaneous decay rates for various isotopes is a wellestablished lab result, backed up by a rich theoretical understanding of
the quantum mechanical processes involved in such decay.
But as soon as we apply these important results from the lab sciences to
the world around us, we obtain results that many creationists find
unacceptable—and a typical response is to reject these well-supported
lab results. Thus, to explain the fact that stars millions of light years
away are visible to us, some creationists have proposed that the speed of
light was much higher in the past than it is today (others have proposed
a version of the 5-minute hypothesis, in which the light we see from
these stars was already almost here when the universe was created about
6,000 years ago). And to explain away the results of radioactive dating
(which, I might add, coheres beautifully with the independently
developed geological time scale), some propose that decay rates are not
constant after all, and were much higher in the past.
In fact, the purported epistemic difference between the lab and the
historical sciences is an illusion. First, with respect to testing our ideas
about the past, witnesses are nothing special. In fact, the memories of
witnesses are often less reliable (by the standards of coherence and
vindication) than other sorts of evidence—the evidence of fingerprints
and DNA tests in criminal investigations; the evidence of archeological
investigations (which sometimes serve to correct historical reports)…
Second, the lab sciences progress by developing extremely general
theories of the basic processes that go on in the world—processes like
gravitational accelerations and mechanical motions in general,
nucleosynthesis in stars (pioneered by Fred Hoyle), chemical changes
and their relation to temperatures, pressures and other important
physical variables, and so on. Such theories are always vulnerable,
since they make so many predictions about what has gone on, and what
will go on in the future. Our conviction that these theories are well
tested and reliable reflects a reasonable standard of proof for science—
but it’s a standard that the historical sciences of geology and biology
also meet.
The standard I’m talking about here combines two features: 1.
Coherence, that is, the processes and principles we accept must fit
together coherently with the observations we make (and vice-versa:
observations are not open-and-shut proofs; in fact they are often
unreliable, and we spend a lot of time establishing the reliability of
various kinds of observations, for example, when we develop new
instruments for particle physics. 2. Vindication; when we reason with
our commitments and reach conclusions about what we should expect to
observe or to happen in various new circumstances, we are vindicated
when our expectations are fulfilled (when our intervention is
successful).
Rationalism and Empiricism. (September 16, 2003)
The point here is to consider just what really goes on in science—we
have these two opposed positions, empiricist and rationalist; the
empiricists (Hobbes, Locke, Berkeley, Hume (and Bacon)) emphasize
the role of observation in scientific knowledge, while the rationalists
emphasize our a priori grasp of certain basic principles that must be our
guide in reasoning about the world (principles like “every event must
have a cause.”)
Coherence and vindication provide a kind of combination of these two
views. Coherence makes little sense in a purely empirical approach,
since any observation stands alone and isolated. Vindication is not
much of a concern to the rationalists, since their principles are known a
priori and not subject to examination, criticism or change.
On to Hutton and Werner—a brief review of their positions & methods
(combining observation with principles, looking for coherence and
vindication): Neither is a pure empiricist, though both cloak their work
in the rhetoric of empiricism.
The Arguments: (September 18, 2003)
Rhetoric and cheap shots vs. Serious arguments—looking at their roles
in science.
The main claim: For reasons that are quite interesting and worth
looking into, but which we will not go into here, the serious arguments,
that is, the evidence and the conclusions drawn from that evidence, do
dominate the development of scientific positions (at least over time).
But, like any other group of people competing for prestige, authority
and other important resources, scientists in general, and the figures we
will be studying, do not rely solely on the power of evidence and careful
argument—rhetoric, personal attacks, ad hominems, subtle put downs &
etc.
Consider the quotes we have here—they range from direct personal
attacks, to subtle denigration, to concrete claims and arguments based
on them.
Outcomes (with a caution re whig history): Hutton is right on basalt,
granite, angular unconformities (and their implications for the vast
duration of geological time). Werner is right on the need for a real
universal stratigraphy, on much of the detailed mineralogy, on the
formation of some veins by precipitation from water. But he is
drastically wrong about the relation between rock types and
stratigraphy, as the subsequent development of biostratigraphy by
Cuvier and Brogniart in France and Smith in England would show.
II. Catastrophists and Uniformitarians.
This debate takes on a more professional, scientific air than the
previous, acrimonious and often highly polemic and personal debates
between Wernerians and Huttonians. But it is extremely intense for all
that.
A. Methods vs. Systems
Uniformitarian method involves applying detailed studies of present
processes (volcanic activity, earthquakes, erosion, sedimentation, etc.)
to the interpretation of the geological record.
The uniformitarian system is a doctrine to the effect that uniformitarian
methods will suffice. That is, the interpretation of the geological
phenomena doesn’t require anything more than present processes
operating at present rates.
Catastrophism, as a method, invokes immense forces and violent events
to interpret some important features of the geological record (such as
the extinctions of groups of fossil species, the contorted and
metamorphosed rocks making up mountainous regions, large beds of
gravel and rocks apparently transported great distances)
The catastrophist system is the doctrine that we need such violent events
in order to make sense of the geological record.
Progressivism (or directionalism) is the view that geological processes
have become less rapid and violent over time. This is compatible with
catastrophism, but many actualists (such as Scrope) agree that the
intensity and rates of geological processes have gradually reduced over
time, while maintaining that the processes themselves remain
fundamentally the same.
This leads to the following table of positions:
Principles of Uniformity (i.e. what is taken to be uniform over time):
Nothing (supernaturalism). No basis for inferring past events from
present evidence, since anything, including creation ex nihilo, is a
possibility. If God is omnipotent, and does not observe any limitations
in how she goes about her business, we have no evidence at all
regarding the past (except perhaps by means of revelation—but of
course we then face the problem of deciding which revelation is the
right one).
Basic Laws (laws of physics & chemistry, roughly). Catastrophists held
that these basic laws have remained in place, but that the conditions
under which they operate (and therefore the processes that have
occurred) have changed dramatically in the course of geological time.
In particular, they claimed that certain dramatic features of the
geological record (mountain ranges, deep cut valleys, massive deposits
of gravel, deep beds of conglomerate rock) record rapid, large,
extremely violent events that have no parallel in our present experience.
An important worry for such views is that we cannot give detailed
predictions about what we should observe, since we cannot make the
necessary calculations to determine what the results of such violent and
complex processes would be. So, while they are in principle tenable
hypotheses about geological history, they are hard to test.
Names: Cuvier, Brogniart, de Beaumont, Buckland, Sedgwick (these
last two shifted more towards actualism over time).
Geological Processes. Actualists hold that the geological processes
presently occurring (volcanic activity, earthquakes, erosion by wind and
water, etc.) are responsible for the geological record we observe. This
has the important methodological advantage that we can study these
processes, and the traces they leave, in great detail right now. As a
result, we can test particular hypotheses regarding the processes
responsible for particular features very thoroughly.
Names: Scrope, Conybeare, Whewell.
Geological processes and their rates and intensities. Uniformitarians
hold both the processes and their rates have been constant. (So
uniformitarians are actualists who reject directionalism/progressivism,
the view—widely popular in the 19th century—that as the earth cools
and ages, the intensity and rate of geological processes is slowly
declining. They may accept that in fact the earth is cooling, but hold
that this has made no difference to geological processes over the period
of time covered by the geological record we now see (an echo here of
Hutton’s “no vestige of a beginning…” remark). The advantage, of
course, is that we can make even more detailed predictions, since
present processes operating at present rates should leave traces that
resemble traces presently forming in all relevant details. The
disadvantage is that there is no a priori reason why the assumption
should hold.
Names: Lyell, Darwin. (Many others were sympathetic, but more
impressed by uniformitarian methods than doctrine.)
The debate: Prevost’s work cast significant doubt on the sudden and
violent nature of transitions between marine, terrestrial and fresh-water
environments in the Paris Basin. Attempts by Buckland and others to
link particular observations (bones buried with gravel in caves, both in
Europe and elsewhere around the world) to the Noachian flood were
cast in doubt by the growing recognition that it was presumptuous at
best to ascribe such scattered phenomena to a single event. Violent,
catastrophist models of the flood such as Elié de Beaumont’s suggestion
that the sudden elevation of the Andes could have produced a tidal wave
that overwhelmed the entire world, were overturned by Scrope’s
observations of loose scoriae that pre-date present river valleys (the
Loire) in central France. They were further undermined by Darwin’s
observations of an earthquake on the Chilean coast, and his persuasive
extension of these observations to a model of the gradual elevation of
the Andes.
More than anything else, the ongoing success of actualist/uniformitarian
methods (Scrope in central France, Lyell on Etna, on freshwater marls,
and on tertiary stratigraphy, Darwin on the Andes and coral atolls)
pushed geologists to broader and increasingly successful actualist and
uniformitarian accounts of more and more geological phenomena. The
next chapter deals with a family of phenomena that resisted satisfactory
treatment for some time.
But the most dramatic and persistent problem for Lyell was not a
specifically geological phenomenon. It was the fossil record, with its
clear pattern of change through time. More modern looking animals,
plants, etc. appear as geological time ranges from the Paleozoic to the
Cenozoic. There is an arrow of time here, an arrow that is indispensable
to the working geologist. But Lyell’s uniformitarianism, strictly read,
allows for no such arrow: conditions, on average, ought to be more or
less the same throughout geological history, if he is right. Reconciling
this uniformity with the pattern of life’s development over time was a
problem to which Lyell had no satisfactory response. (One response he
did try was to suggest that there were cycles of conditions & climate
that could repeat themselves, along with the life-forms that were suited
to them—so that, in the long run, even the arrow of life’s development
was really a closed circle. But of course he had no evidence to support
this suggestion.)
Methods: The use of fossil correlation is crucial to the development of
geology in this period. Fossil content of formations is used by Lyell to
separate the tertiary into the Eocene, Miocene, Pliocene and … Fossils
are used by Cuvier and Brogniart to map out the formations of the
(tertiary) Paris Basin and establish the repeated sequences of
terrestrial/fresh water/marine environments recorded there. Fossils
guided William Smith in the preparation of the first detailed geological
maps of England. These maps were refined and extended to older
formations in Wales, where the Cambrian, Ordovician and Silurian were
established by Murchison, Sedgwick and Lapworth: After a difficult
controversy arose over the initial overlap of the systems proposed by
Murchison and Sedgwick, Lapworth applied a careful examination of
the fossils found in the rocks of these systems to distinguish them into
three separate systems.
Remark on Hutton: In some respects Hutton’s views sound
catastrophist—his talk of the huge forces and violence involved in
uplift/collapse (a key part of Huttonian cycles) contrasts sharply with
Lyell’s view of uplift and subsidence as gradual processes taking place
all around us even now. But there is an important difference. Cuvier
says that the “thread of operations is broken,” by which he seems to
imply that the processes he claims to have occurred in the past are no
longer in operation at all—but for Hutton, these violent processes are
quiescent, but still in place, and though we have yet to witness them, in
time (oh dear!) we will.
What’s
Uniform
Advantages
Supernaturalism Catastrophism Actualism
Nothing
Basic Laws
Geological
Processes
No limits,
therefore
immune from
test &
refutation.
Disadvantages Ditto. No basis
for doing
science.
Uniformitarianism
Geological
Processes and
Their Rates
Any process
Can study
Can study present
allowed by
present
processes in detail
basic physics processes to and apply it all to
and chemistry help
reading the
is grist for the interpret the geological record.
mill.
geological
record.
Hard to model Present
There may be
complex
processes
events in the past
processes no
may not be that just won’t fit;
longer
enough.
problem of
occurring,
If rates vary identifying
therefore hard a lot, may
average rates,
to apply, test
be hard to
how much
or vindicate
interpret.
variation.
The Ice Age:
There are a number of interesting geological phenomena that were
poorly understood in the 1820’s and 30’s. These included complex
beds of varied sediments, unsorted debris now called “till,” parallel
grooves carved in the bedrock of some areas, and (most dramatically)
erratic boulders, some of immense size, scattered across the
countryside, that had apparently traveled large distances from their
place of origin. These had been attributed to the Noachian deluge by
the diluvialists, but their models of the flood were loose and largely
hand-waving, and provided no testable account of these phenomena.
But even as the notion of a single, universal flood was dropped, appeals
to massive and violent flooding to explain some of these phenomena
persisted. Lyell and others proposed an alternative, based on a period of
higher sea level combined with cooler climate: the drift hypothesis.
Icebergs were supposed to have carried loads of material, including
sediments and erratics, and dropped them as they melted, following
currents and often lodged against the bottom where the waters grew
shallow.
A radical alternative emerge in the late 1830’s—the glacial theory.
(Hutton anticipated this account in some respects, but only in passing.)
The theory was first suggested in something like its present form by a
chamois hunter, Jean-Pierre Perraudin, who had reached his conclusions
about 1815. An engineer, Ignace Venetz, was sympathetic to his views,
and traced evidence of former glacial action still further from their
present haunts. Venetz first presented his views at a meeting of a
natural history society in 1821, and continued to pursue his
investigations through the 1820’s, announcing an extended and
expanded vision of the glacial theory in 1829. Though generally
rejected out of hand, the theory was taken up by Jean de Charpentier,
who was yet another step up the pecking order: director of a salt mine,
and a well-respected naturalist. In 1834, in Lucerne, Switzerland,
Charpentier read a paper announcing his results, and crediting Venetz’
pioneering work. He invoked glacial action to account for polished and
striated rock surfaces, erratics and other phenomena. One skeptic in the
audience was Louis Agassiz, a brilliant and energetic protégé of
Cuvier’s who had made his reputation with a massive work on the
anatomy of fossil fish. A friend of Charpentier’s, Agassiz traveled with
Charpentier in the summer of 1836, looking at glacial phenomena in the
Diablerets and Rhone Valley. Dubious at first, he was finally
converted.
As a student of Cuvier’s, Agassiz was strongly inclined to view these
phenomena in catastrophist terms. He went on to propose an extremely
fanciful and dramatic account of the “ice age” (die Eiszeit—the term is
due to Karl Schimper). Though he acknowledged Charpentier’s
priority, his immense energy and enthusiasm led him, more than
Charpentier, to be identified as the chief proponent of the glacial theory;
this led to a serious rift between Agassiz and his old friend. Again, the
general reaction to the idea was skeptical. This time, though Agassiz
fame and energy failed to convince in the lecture hall, they at least
persuaded many leading geologists to examine the evidence. And
again, a good look at the field evidence was widely (though never
universally) convincing. Agassiz’ book on the ice age appeared in
1840; Charpentier’s much more carefully argued case appeared a year
later.
(Other names here: Bernhardi—northern Germany; Esmark—Norway.)
In 1840 Agassiz traveled to England, where he worked assiduously at
converting prominent English geologists to the glacial theory. He
caused “a great stir,” though not a total conversion. And many
geologists on both sides of the debate turned their attention to the
evidence for glacial action in the British Isles. By 1846, Agassiz had
gone on to North America to continue his glacial campaign. By 1844,
glacial theory was triumphant in its homeland of Switzerland. Lyell
was not persuaded fully until 1857. The continued opposition to glacial
action as an account of striations, polished surfaces and till deposits (by
the younger de Luc and Murchison) was greatly undermined when a
dam burst, investigated by T.F. Jamieson (published 1862), failed to
produce any such phenomena.
This is a wonderful case study in the development, promotion and final
acceptance of a once-radical hypothesis. As Hallam points out, the
wilder aspects of Agassiz’ account probably delayed the theory’s
acceptance; uncertainties over the physics of ice-flow over nearly
horizontal terrain, over exactly how ice could polish and striate rocks
(the importance of the rocks carried within the glacier as giving it teeth
was not immediately obvious), and over the significance of marine
shells found in glacial till (finally identified as erratics in their own
right, by Croll and Tiddeman), also delayed general acceptance. By the
1870’s, acceptance was more or less universal, and a new and recent
chapter added to our geological histories.
This also leads to a worthwhile philosophical discussion, about the
nature of facts. The distinction between fact and theory plays an
important rhetorical role in debates over evolution and the age of the
earth; one popular way to dismiss a claim is to say, “Well, that’s just
theory!” This trades on the popular use of “theory” to mean a
speculative, and often merely personal, account. But in science, what
we mean by a theory is a complex account of some phenomena that
gives an explanation of them, and that has some testable consequences.
So in the first place, theories are not just speculative, anything goes
sorts of things. In the second place, facts are not just a matter of “brute
observations.” There are many facts that we are perfectly confident of
despite a lack of direct observations, such as the shape (roughly
hemispherical) of the back side of the moon, which wasn’t observed
until the early days of the space program, with the Ranger probes. The
ice age is treated as established fact today, and various theories are
advanced to explain what triggers ice ages, to predict more details of the
flow of ice over large regions (which depends on how precipitation is
distributed, the details of how ice behaves under high pressure, and the
effects of meltwater flowing through and beneath glaciers, among other
things), and so on.
The Age of the Earth
By the mid-19th century, actualist/uniformitarian methods had spread
widely, and their success in treating a wide range of geological
phenomena was generally recognized even by geologists who did not
share Lyell’s hard line substantive uniformitarianism. The idea that
geological time was immense had been generally accepted, even by the
catastrophists; just how immense it might be was suggested by Lyell’s
treatment of Etna, which showed that late tertiary formations (a very
recent geological period) dated back to something like 10 million years
ago.
The stratigraphy of the phanerozoic (the period in which fossil life is
fairly abundant, including the Paleozoic, Mesozoic and Cenozoic) was
well-established, and geologists were hard at work refining the details.
The pre-Cambrian was largely a mystery, since the general absence of
fossils made correlation of strata below the Cambrian very difficult.
But the success of uniformitarian methods depended on the availability
of time—if time limits are imposed, then present processes and rates
might not suffice even if, given enough time, they would. For Lyell, a
further “draft on the bank of time” was always the right move—so long
as the observed phenomena (the traces) could be explained by appeal to
present processes acting over some period of time, it was always
preferable, in his view, to help yourself to the time needed rather than
try to invent (and model) entirely new processes.
The science of thermodynamics (the physics of heat & energy) was
becoming quite sophisticated at this time—it was initially developed to
make sense of the workings of steam engines (especially to explain their
efficiency, which differed widely). Its mathematical formulation was
pursued by figures including Fourier and William Smith (later Lord
Kelvin). One of the principle results was the second law, which rules
out the possibility of perpetual motion heat engines. Since the earth’s
geological processes (and the sun’s radiation) were apparently the result
of heat energy, this theory had immediate implications for our ideas
about the sun and the earth.
Darwin published his Origin of Species in 1859, presenting his evidence
for evolution as well as his proposed mechanism (natural selection).
Darwin’s views included a strong commitment to Lyell’s uniformitarian
approach to geology, which Darwin himself has successfully applied to
various geological questions during the voyage of the Beagle. But this
was not just a matter of Darwin’s preferences as a geologist—his theory
of how evolution occurs, as he acknowledged, would require long
periods of time for the present variety of complex life to arise: For
Darwin variations arise accidentally and are not directed by any
teleological (end-seeking) force. As a result, life evolves only as
advantageous variations happen to arise and be ‘selected for.’
In Origin, Darwin actually presented a calculation of the time required
to erode a large region of south-east England called the Weald; his
result was a figure of 300 million years, a number that fit nicely with the
broad sense that his mechanism for evolution would require an immense
time to operate in. But Darwin’s calculation was widely criticized, and
he backed down rather quickly (it was qualified in the 2nd edition, and
removed entirely in the 3rd).
In 1862, shortly after Origin appeared, William Thompson (later Lord
Kelvin) published a calculation of the time during which the sun could
be expected to continue radiating energy at its current rate. Based on
Helmholtz’ gravitational theory of the sun’s energy (gravitational
potential energy in a dispersed mass equivalent to the sun being far
greater than any amount of chemical energy such a mass could contain),
Kelvin concluded that the sun probably did not have sufficient energy to
continue its present output for 100 million years, and almost certainly
didn’t have enough to continue for 500 million years. Hence, as he
concluded, the time available for geology and for paleontology must be
limited within some such figure; as a result, of course, he completely
dismissed Darwin’s calculation of the “denudation of the Weald”.
Kelvin later applied similar thermodynamic considerations to the earth,
based on a simple model of the earth’s history in which it cooled slowly
as a roughly homogeneous molten mass of uniform temperature
(convection currents maintaining even temperature during the cooling).
Once the earth solidifies, on Kelvin’s model, it begins a gradual cooling
that depends on four basic quantities: The initial temperature (= the
temperature of fusion for the earth’s rocky material), the conductivity of
the earth’s material, and its heat capacity. Straightforward calculations
based on these figures, combined with a temperature profile indicating
how quickly the earth’s temperature rises as we descend deeper into the
earth’s interior gives a figure for the earth’s present age. The result of
this calculation was a best estimate of 98 million years, with a lower
limit of 20 million, and an upper limit of 400 million. (Kelvin also
applied tidal friction and its effect on the earth’s speed of rotation to
calculate another limit on the earth’s age.)
At this point (during the 1860’s, roughly) Kelvin remained quite modest
in his claims. He did not seem as concerned about the specific limits as
he was about the point of principle, viz. that some limit on geological
time was inevitable: The earth cannot be a perpetual motion machine.
But this modesty was to change over the next two decades…
Beginning with Philips calculation of 1861, based on the accumulation
of sedimentary rock since the Cambrian (= start of the Paleozoic), a
series of geological efforts to arrive at a geological time scale were
undertaken. These include Croll, who focused on climate change and
an astronomical model of ice ages, T. Mellard Reade, who included
both solvent erosion and mechanical erosion, and Samuel Haughton,
who based his calculations on a supposed link between climate (as
indicated by fossil remains) and the earth’s temperature, whose initial
figure of 2300 million years was very appealing to uniformitarians, but
who later sought to bring his results more in line with Kelvin’s
requirements. Clarence King, of the U.S. Geological Survey,
constructed graphs representing the earth’s cooling over time
embodying Kelvin’s methods combined with new figures for the
melting temperature and heat capacity of the earth, obtaining a result of
22-24 million years. And John Joly made a calculation based on the
accumulation of salt in the oceans. He assumed that rivers dissolve and
carry salt into them steadily over time, and that the salt remains in the
oceans indefinitely (while the water evapourates and replenishes the
rivers as rain). The resulting estimate, after some sophisticated analysis,
put the age of the oceans (which Joly took to correspond to the time sine
the earth’s temperature fell below the boiling point) at 80-90 million
years.
With the drastically shorter estimate from King (and Kelvin’s increasing
insistence on shorter limits as well), geologists began to resist the
physical estimates more vigourously, beginning in the 1880’s and 90’s.
Osmond Fisher, who had other reasons for supposing the earth to be
“plastic” below the crust, argued that allowing for some convection
currents in the lower earth would have a drastic impact on Kelvin’s
figures. Archibald Geicke argued that the independent evidence of
geology could not be neglected in evaluating the physical calculations.
John Perry, a former assistant to Kelvin, explored alternatives to
Kelvin’s assumptions including convection and greater conductivity,
and demonstrated that they would allow for considerably more time.
Kelvin responded by insisting on his new calculations (Kelvin, 1897:
On the Age of the Earth as an Abode Fitted for Life), which allowed a
maximum of 24 million years for the earth’s age. Geicke rejected this
outright, as did T.C. Chamberlin, in a reply to Kelvin’s paper.
Chamberlin proposed a slow accretion model allowing more time for
the earth to continue in more or less its present state, and speculated,
prophetically, that the sun’s energy might be due to unknown processes
that release energies at the atomic level.
By this time radioactivity had been discovered (by Becquerel); in 1903
Pierre Curie and his assistant realized that radium salts release heat at a
very steady rate. Rutherford (perhaps the greatest experimental
physicist of the 20th Century) realized by 1904 that all radioactive
elements contained vast amounts of energy that was released in
radioactive decay. In the spring of 1904, Rutherford lectured on the
topic of radioactivity at the Royal Institution; in that lecture (which
Kelvin attended) Rutherford pointed out the implications for Kelvin’s
calculations of the earth’s age: a source of replacement energy for the
heat lost to space had been found. We no longer needed to regard the
earth as a body that was steadily cooling over time. Analyses by Strutt
showed that the amount of radioactivity measured in igneous rocks was
far more than that required to maintain the earth’s temperature—so it
seemed (unless radioactive materials were far more concentrated in the
crust than deeper in the earth’s interior) the earth might even be heating
up, or have other ways of releasing the heat being produced.
It soon became apparent that radioactive decay finished by producing
non-radioactive elements, and that the rate of decay was described by a
simple exponential equation. The possibility of measuring the amount
of decay that had occurred by identifying how much of the original
material (“parent isotope”) had been converted into a stable, nonradioactive final product (“daughter isotope”), and thereby determining
the age of various rocks, was now obvious, and work on making such
measurements began very quickly. There were many technical details
to be sorted out (at first, the existence and nature of different isotopes of
the same element was not understood; once this puzzle was worked out,
the techniques were greatly improved). But from the start the results
suggested far larger ages than had previously been accepted either by
the physicists or most geologists.
Joseph Barrell’s 1917 article, “Rhythms and the measurement of
geological time,” was a turning point, establishing the radioactive
methods as the best means for estimating geological time. His
argument clearly identified key problems with the other geological
methods, and why so many of them had produced substantial underestimates of the earth’s age; just to mention one, the existence of many
substantial new mountain ranges means that erosion is now proceeding
far faster than it has on average over the earth’s history. His figure for
the bottom of the Cambrian was 550-700 million years—well in accord
with contemporary figures of about 556 million years (Harland, W.B. et
al., 1990. A geologic time scale, 1989 edition. Cambridge University
Press: Cambridge, p.1-263.)
Subsequent developments have refined techniques, improved reliability,
and added further methods based on other radioactive elements that
serve to cross-check and verify the results of these measurements.
Detailed but accessible accounts of these techniques can be found in
many texts, and on the web at talkorigins.org.
Hallam finishes with a discussion of gradualism in geology and biology
(an important topic for Darwin). He argues that the “reality” of the
Cambrian explosion remains a serious problem for the gradualist. Some
claim that the explosion records only an explosion in the number of
forms of life with mineralized skeletons and shells; earlier fossils of a
wide range of animal life have been found, including recent evidence of
a very early proto-vertebrate on the order of 700 million years old. But
the Cambrian explosion issue remains one of the most controversial and
interesting problems in paleontology (and has attracted more than its
share of attention from creationists eager to use it as a club to beat
evolution with).
Continental Drift.
From its first beginnings, in the work of Osmond Fisher, F.B. Taylor,
and, later, Alfred Wegner, the idea of continental drift was controversial
and exciting. It found supporters early on, but also (and more
influential) it found some very aggressive critics, including Dr. –later
“Sir”— Harold Jeffreys. While Wegner developed some very
persuasive evidence for his theory, evidence that is regarded as very
telling today, he also made some embarrassing mistakes, proposed some
dubious arguments for it, and had no credible account of the forces and
conditions in the earth that would allow for continental drift.
Notes for 2233 Lectures on Evolution: Evidence for evolution.
Evolution and Natural Selection vs. Creation
The key issue at this point is to get clear about the contrast between these views. Creationism as
a contemporary movement is a “big tent,” including many very different opponents of
naturalistic accounts of evolution. Their main point of agreement is that they all wish to invoke
some sort of creator/designer as part of their understanding of the universe, and reject as
inadequate or just plain false any view that attempts to dispense with this creator.
1. Conditions for natural selection:
The conditions under which natural selection will operate:
a. Significant Variation (SV). This is variation amongst individuals in a
population that makes a difference to survival and reproduction (i.e. to their
“representation” via descendents in subsequent generations).
This results (in biology) from two conditions that can be seen to hold: 1. The
broad range of variations that arise in living populations. 2. The struggle for
existence: Most organisms (in the medium run) must fail to leave any
descendents.
b. Inheritance of SV. At least some significant variation must have a tendency
to be inherited, i.e. the offspring of individuals must have a higher probability
of having some significant variation present in the parent(s) than a randomly
selected member of their generation.
It’s worth noting that this condition is very weak—it does not assume
anything about the processes involved in inheritance (unlike, say, Lamark’s
inheritance of acquired characteristics).
c. Stability. Circumstances making some of the inheritable SV advantageous
must be persistent over a substantial number of generations. (Note that this
covers selection against some traits implicitly, since, given our definitions
above, those who fail to have such traits will be judged to have an
advantageous inheritable trait).
With these conditions in place, over time the most probable pattern of change
will lead the population towards a state where every member of the population will have
the inheritable SV traits. Given long enough periods of stability together with a
significantly advantageous and heritable SV, this probability becomes a practical
certainty. We can regard a and b above as more fundamental, since natural selection
could be said to occur even if stability fails to hold—but the upshot will not be any
stable trend tending to make the population change in any particular way. In that case,
over the medium to long run, the frequency of various traits in the population will tend
to vary randomly, and drift will be the right explanation of any long term changes.
2. Limiting NS.
There are a number of conditions that may place significant limits on how far NS can
go in altering the characteristics (distribution of heritable traits) of a population.
a. Limits on variability. The most obvious way to limit this would be to deny
that there are any sources of new, heritable variation. A more subtle limit
denies that there are any sources of new, heritable and advantageous
variation. Either way, NS will be able to change the population, but only by
driving out any initial, disadvantageous traits—once that is done, there will
either not be any new variation (the first limit), or all the variation there is
will simply introduce new, disadvantageous traits that will subsequently be
driven back out of the population. (The second strategy is often employed by
creationists and ID theorists, who insist, on a variety of spurious grounds, that
all mutations are disadvantageous. The first strategy is older, and usually
cast in the form of some kind of species-essentialism.)
b. Improbability of advantageous variations. This is a still subtler move with
the same aim. Defenders of this limitation on NS argue that advantageous
variations are typically complex (involving a number of very specific
changes that must be combined in one or a very few steps). Since each
specific change is highly improbable and the changes are independent of each
other (i.e. each is no more or less likely given that some other(s) have
occurred), the probability of a substantial number of these happening together
(which would be required if any advantage were to result) is vanishingly
small. This is the strategy M. Behe pursues in Darwin’s Black Box, and also
(with different window-dressing) the strategy of W. Dembski’s The Design
Inference and No Free Lunch.
Evidence for evolution:
1. Taxonomy:
The hierarchical structure of taxonomy in biology: the fundamental pattern is one of
shared similarities as the basis for taxonomic groups, with species sharing the greatest
number of these similarities, genus sharing a smaller set, families still smaller, and so on,
all the way up to phyla and kingdoms. If such similarities are shared because of descent
with modification, then we have a credible explanation for the pattern.