Uniformitarianism, also known as the Doctrine
of Uniformity, refers to the invariance in
the principles underpinning science, such
as the constancy of causality, or causation,
throughout time, but it has also been used
to describe invariance of physical laws through
time and space.
Though an unprovable postulate that cannot
be verified using the scientific method, uniformitarianism
has been a key first principle of virtually
all fields of science.In geology, uniformitarianism
has included the gradualistic concept that
"the present is the key to the past" (that
events occur at the same rate now as they
have always done); many geologists now, however,
no longer hold to a strict theory of gradualism.
Coined by William Whewell, the word was proposed
in contrast to catastrophism by British naturalists
in the late 18th century, starting with the
work of the geologist James Hutton in his
many books including Theory of the Earth.
Hutton's work was later refined by scientist
John Playfair and popularised by geologist
Charles Lyell's Principles of Geology in 1830.
Today, Earth's history is considered to have
been a slow, gradual process, punctuated by
occasional natural catastrophic events.
== History ==
=== 18th century ===
The earlier conceptions likely had little
influence on 18th-century European geological
explanations for the formation of Earth.
Abraham Gottlob Werner (1749–1817) proposed
Neptunism, where strata represented deposits
from shrinking seas precipitated onto primordial
rocks such as granite.
In 1785 James Hutton proposed an opposing,
self-maintaining infinite cycle based on natural
history and not on the Biblical account.
The solid parts of the present land appear
in general, to have been composed of the productions
of the sea, and of other materials similar
to those now found upon the shores.
Hence we find reason to conclude:1st, That
the land on which we rest is not simple and
original, but that it is a composition, and
had been formed by the operation of second
causes.
2nd, That before the present land was made,
there had subsisted a world composed of sea
and land, in which were tides and currents,
with such operations at the bottom of the
sea as now take place.
And,
Lastly, That while the present land was forming
at the bottom of the ocean, the former land
maintained plants and animals; at least the
sea was then inhabited by animals, in a similar
manner as it is at present.Hence we are led
to conclude, that the greater part of our
land, if not the whole had been produced by
operations natural to this globe; but that
in order to make this land a permanent body,
resisting the operations of the waters, two
things had been required;
1st, The consolidation of masses formed by
collections of loose or incoherent materials;
2ndly, The elevation of those consolidated
masses from the bottom of the sea, the place
where they were collected, to the stations
in which they now remain above the level of
the ocean.
Hutton then sought evidence to support his
idea that there must have been repeated cycles,
each involving deposition on the seabed, uplift
with tilting and erosion, and then moving
undersea again for further layers to be deposited.
At Glen Tilt in the Cairngorm mountains he
found granite penetrating metamorphic schists,
in a way which indicated to him that the presumed
primordial rock had been molten after the
strata had formed.
He had read about angular unconformities as
interpreted by Neptunists, and found an unconformity
at Jedburgh where layers of greywacke in the
lower layers of the cliff face have been tilted
almost vertically before being eroded to form
a level plane, under horizontal layers of
Old Red Sandstone.
In the spring of 1788 he took a boat trip
along the Berwickshire coast with John Playfair
and the geologist Sir James Hall, and found
a dramatic unconformity showing the same sequence
at Siccar Point.
Playfair later recalled that "the mind seemed
to grow giddy by looking so far into the abyss
of time", and Hutton concluded a 1788 paper
he presented at the Royal Society of Edinburgh,
later rewritten as a book, with the phrase
"we find no vestige of a beginning, no prospect
of an end".Both Playfair and Hall wrote their
own books on the theory, and for decades robust
debate continued between Hutton's supporters
and the Neptunists.
Georges Cuvier's paleontological work in the
1790s, which established the reality of extinction,
explained this by local catastrophes, after
which other fixed species repopulated the
affected areas.
In Britain, geologists adapted this idea into
"diluvial theory" which proposed repeated
worldwide annihilation and creation of new
fixed species adapted to a changed environment,
initially identifying the most recent catastrophe
as the biblical flood.
=== 19th century ===
From 1830 to 1833 Charles Lyell's multi-volume
Principles of Geology was published.
The work's subtitle was "An attempt to explain
the former changes of the Earth's surface
by reference to causes now in operation".
He drew his explanations from field studies
conducted directly before he went to work
on the founding geology text, and developed
Hutton's idea that the earth was shaped entirely
by slow-moving forces still in operation today,
acting over a very long period of time.
The terms uniformitarianism for this idea,
and catastrophism for the opposing viewpoint,
were coined by William Whewell in a review
of Lyell's book.
Principles of Geology was the most influential
geological work in the middle of the 19th
century.
==== Systems of inorganic earth history ====
Geoscientists support diverse systems of Earth
history, the nature of which rest on a certain
mixture of views about process, control, rate,
and state which are preferred.
Because geologists and geomorphologists tend
to adopt opposite views over process, rate
and state in the inorganic world, there are
eight different systems of beliefs in the
development of the terrestrial sphere.
All geoscientists stand by the principle of
uniformity of law.
Most, but not all, are directed by the principle
of simplicity.
All make definite assertions about the quality
of rate and state in the inorganic realm.
==== Lyell's uniformitarianism ====
According to Reijer Hooykaas (1963), Lyell's
uniformitarianism is a family of four related
propositions, not a single idea:
Uniformity of law – the laws of nature are
constant across time and space.
Uniformity of methodology – the appropriate
hypotheses for explaining the geological past
are those with analogy today.
Uniformity of kind – past and present causes
are all of the same kind, have the same energy,
and produce the same effects.
Uniformity of degree – geological circumstances
have remained the same over time.None of these
connotations requires another, and they are
not all equally inferred by uniformitarians.Gould
explained Lyell's propositions in Time's Arrow,
Time's Cycle (1987), stating that Lyell conflated
two different types of propositions: a pair
of methodological assumptions with a pair
of substantive hypotheses.
The four together make up Lyell's uniformitarianism.
===== Methodological assumptions =====
The two methodological assumptions below are
accepted to be true by the majority of scientists
and geologists.
Gould claims that these philosophical propositions
must be assumed before you can proceed as
a scientist doing science.
"You cannot go to a rocky outcrop and observe
either the constancy of nature's laws or the
working of unknown processes.
It works the other way around."
You first assume these propositions and "then
you go to the outcrop."
Uniformity of law across time and space: Natural
laws are constant across space and time.The
axiom of uniformity of law is necessary in
order for scientists to extrapolate (by inductive
inference) into the unobservable past.
The constancy of natural laws must be assumed
in the study of the past; else we cannot meaningfully
study it.Uniformity of process across time
and space: Natural processes are constant
across time and space.Though similar to uniformity
of law, this second a priori assumption, shared
by the vast majority of scientists, deals
with geological causes, not physico-chemical
laws.
The past is to be explained by processes acting
currently in time and space rather than inventing
extra esoteric or unknown processes without
good reason, otherwise known as parsimony
or Occam's razor.
===== Substantive hypotheses =====
The substantive hypotheses were controversial
and, in some cases, accepted by few.
These hypotheses are judged true or false
on empirical grounds through scientific observation
and repeated experimental data.
This is in contrast with the previous two
philosophical assumptions that come before
one can do science and so cannot be tested
or falsified by science.
Uniformity of rate across time and space:
Change is typically slow, steady, and gradual.Uniformity
of rate (or gradualism) is what most people
(including geologists) think of when they
hear the word "uniformitarianism," confusing
this hypothesis with the entire definition.
As late as 1990, Lemon, in his textbook of
stratigraphy, affirmed that "The uniformitarian
view of earth history held that all geologic
processes proceed continuously and at a very
slow pace."Gould explained Hutton's view of
uniformity of rate; mountain ranges or grand
canyons are built by accumulation of nearly
insensible changes added up through vast time.
Some major events such as floods, earthquakes,
and eruptions, do occur.
But these catastrophes are strictly local.
They neither occurred in the past, nor shall
happen in the future, at any greater frequency
or extent than they display at present.
In particular, the whole earth is never convulsed
at once.Uniformity of state across time and
space: Change is evenly distributed throughout
space and time.The uniformity of state hypothesis
implies that throughout the history of our
earth there is no progress in any inexorable
direction.
The planet has almost always looked and behaved
as it does now.
Change is continuous, but leads nowhere.
The earth is in balance: a dynamic steady
state.
=== 20th century ===
Stephen Jay Gould's first scientific paper,
Is uniformitarianism necessary?
(1965), reduced these four assumptions to
two.
He dismissed the first principle, which asserted
spatial and temporal invariance of natural
laws, as no longer an issue of debate.
He rejected the third (uniformity of rate)
as an unjustified limitation on scientific
inquiry, as it constrains past geologic rates
and conditions to those of the present.
So, Lyellian uniformitarianism was unnecessary.
Uniformitarianism was proposed in contrast
to catastrophism, which states that the distant
past "consisted of epochs of paroxysmal and
catastrophic action interposed between periods
of comparative tranquility" Especially in
the late 19th and early 20th centuries, most
geologists took this interpretation to mean
that catastrophic events are not important
in geologic time; one example of this is the
debate of the formation of the Channeled Scablands
due to the catastrophic Missoula glacial outburst
floods.
An important result of this debate and others
was the re-clarification that, while the same
principles operate in geologic time, catastrophic
events that are infrequent on human time-scales
can have important consequences in geologic
history.
Derek Ager has noted that "geologists do not
deny uniformitarianism in its true sense,
that is to say, of interpreting the past by
means of the processes that are seen going
on at the present day, so long as we remember
that the periodic catastrophe is one of those
processes.
Those periodic catastrophes make more showing
in the stratigraphical record than we have
hitherto assumed."Even Charles Lyell thought
that ordinary geological processes would cause
Niagara Falls to move upstream to Lake Erie
within 10,000 years, leading to catastrophic
flooding of a large part of North America.
Modern geologists do not apply uniformitarianism
in the same way as Lyell.
They question if rates of processes were uniform
through time and only those values measured
during the history of geology are to be accepted.
The present may not be a long enough key to
penetrate the deep lock of the past.
Geologic processes may have been active at
different rates in the past that humans have
not observed.
"By force of popularity, uniformity of rate
has persisted to our present day.
For more than a century, Lyell's rhetoric
conflating axiom with hypotheses has descended
in unmodified form.
Many geologists have been stifled by the belief
that proper methodology includes an a priori
commitment to gradual change, and by a preference
for explaining large-scale phenomena as the
concatenation of innumerable tiny changes."The
current consensus is that Earth's history
is a slow, gradual process punctuated by occasional
natural catastrophic events that have affected
Earth and its inhabitants.
In practice it is reduced from Lyell's conflation,
or blending, to simply the two philosophical
assumptions.
This is also known as the principle of geological
actualism, which states that all past geological
action was like all present geological action.
The principle of actualism is the cornerstone
of paleoecology.
== See also ==
Astronomical spectroscopy
Catastrophism
Gradualism
History of geology
History of paleontology
Paradigm shift
Perfect Cosmological Principle
Physical constant
Physical Cosmology
Scientific consensus
Time-variation of fundamental constants
== Notes
