Transcript METAMORPHISM & METAMORPHIC ROCKS

FLOODS, FOSSILS AND
HERESIES
“NO VESTIGE OF A BEGINNING,
NO PROSPECT OF AN END”JAMES HUTTON
James Hutton
Father of Geology
Pre Age of Enlightment
 Bishop Ussher 1654
 Biblical Chronology
 Based on generations
 Earth created on October 23, 4004
B.C. at 9AM
FOSSILS
 Recognizable evidence of pre-existing life
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Perfect preservation of organisms
Impressions- casts and molds
Shells- original or replaced
Bones- original or replaced
Plant structures- trunks, leaves
Trace fossils- tracks, burrows, borings
Fecal matter (coprolites)
Da Vinci’s Insight
 In 1500 C.E. Leonardo Da Vinci recognized
that fossil shells in the layered rocks
represented ancient marine life
 Observed that many fossil rich layers were
separated by unfossiliferous layers thereby
repudiating the concept of one flood
 Had the idea that seasonal events responsible
Nicolas Steno
 Danish Naturalist and Physician working for the
Duke of Tuscany
 Widely circulated writings
 Fossils formed together with the rocks in which
they occur
 1669 stated the 3 most basic principles
 Stratification- horizontal layering
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Inferred that differences in strata reflected
differences in conditions (temperature, wind,
currents, storms)
Principles Used to Determine
Relative Age- Nicolas Steno
 Original Horizontality Because particles settle from fluids under gravity,
stratification MUST be horizontal
 Superposition
 Progressively younger from bottom => top
 Lateral Continuity
 Strata originally extended in all directions until it
thinned to zero or terminated at margin (basin of
deposition)
Unconformities
 Unconformity - surface that represents a gap
in the geologic record
Disconformity - contact representing missing
parallel beds of sedimentary beds
 Angular unconformity - younger strata overlie
an erosion surface on tilted or folded layers
 Nonconformity - erosion surface on igneous or
metamorphic rock
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Utility of Fossils
 John Woodward
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1723, Correlation of strata in England and
European mainland based on “great numbers of
shells”
 Geologic Mapping
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1746, crude geologic map showed continuity of
chalk beneath the English Channel
William Smith, canal engineer
 The Map that Changed the World,
 1796 wrote “wonderful order and regularity
with which nature has disposed of these
singular productions [fossils] and assigned to
each its class and peculiar stratum”
 1815 Publication of the 1st geologic map of
England intended for the development of
canals, quarries and mines as well as natural
resources
William Smith’s "Strata Identified by
Organized Fossils"
 Soon after the first issue of his great geological map of England in 1815,
William Smith published the Strata Identified by Organized Fossils.
 It was intended as a kind of geological users manual with illustrations to
identify fossils.
 But Smith’s work went beyond the mere illustration of fossils. Smith had
deciphered the hieroglyphics of nature-the distinctive inscriptions borne
by the different strata. With the Strata Identified . . . and its colored plates
in hand, anyone would be able to compare the plates with fossils collected
in the field and immediately identify the strata from which they came.
 The strata once identified, their place in the orderly succession of the
strata-which lay above and which lay below, as Smith had determined it was then known. All this, Smith wrote, "without the necessity of deep
reading, or the previous acquirement of difficult arts."
Georges Cuvier and Alexandre
Brongniart- Paris Basin
 Development of geologic map of Paris Basin
 The strata of the Paris Basin were close to horizontal.
As of
 1811, Cuvier and Brongniart employed fossils but
only in the few instances where more obvious
evidences of sequence were absent.
 The title of their work was Géographie Minéralogique
by which they meant the distribution of what Werner
had called the "external" characteristics of the mineral
and fossil contents, shapes, colors, and textures of the
strata within the Paris basin.
 Today call this lithology. They determined the order of
the strata from their superposition, their lithology and
by tracing them across the basin
 Cuvier firmly established the fact of the extinction of
past lifeforms
Correlation
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Physical Continuity of Lithologic Units
Similarity of Rock Types
Superposition
Correlation by Fossils
Principle of Faunal Succession
 Index Fossil
 Fossil Assemblage
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Correlation
 Correlation by Fossils
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Principle of Faunal Succession
• Wm. Smith & Georges Cuvier
• Organism succeed one another in lithologic strata
• One organism will NOT be found in rocks of widely
different ages
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Index Fossil
Easily recognizable/Easily identifiable
• Wide geographic distribution
• Of limited life span as a species
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Fossil Assemblage
Explanation of Change Among
Fossils
 Catastrophism
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Cuvier firmly established the fact of the extinction of
past lifeforms
Believed in wholesale catastrophic events caused
extinctions
With each catastrophe life move progressively towards
ultimate “perfection”
 Descent by Evolution
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Younger organisms are the descendents of older ones
Species change through time- Charles Darwin
Unified Hypotheses of the Earth
 Cosmogonists
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Human search for understanding
Understanding God through his work (Nature)
and his word (Scripture)
All inclusive hypotheses to explain origin of
universe, earth and life
• Earth originally hot, cooled, water and atmosphere
began segregated, interior still hot
 Buffon
 Geologic Chronology
Buffon
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18th century thinker
34 volume Histoire Naturelle, 1749
Molten origin of Earth
Solar system originated from pieces of the sun
breaking of through asteroid collisions
 Estimated age of Earth at 75,000 yrs
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Calculated from cooling steel balls
First to question literal significance of the 6 days of
creation, “a year is to God as a thousand years to man”
Geologic Chronology
 Buffon’s speculative chronology- 6 distinct
epochs
 Recognition of rock divisions (coal measures
in England by 1719)
 J. Lehmann distinguishes gently dipping
stratified fossiliferous rocks from more
‘primitive’ deposits
 1759 Arduino distinguished Primitive,
Secondary, Tertiary and Volcanic
Neptunism
 A.G. Werner (1787) believed all rocks
precipitated from a retreating ocean
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Neptunist
Primitive, Transition, Secondary and Alluvial
Considered earth to be static
 Basalt Controversy
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Volcanic rock
Seen to crystallized from lava
Could not be from a neptunian origin
James Hutton and Plutonism
 Dynamic Earth
 Earth ever changing
 Modern earth processes capable of having produced
landscape given enough time
 Geologic processes act slowly
 Interpretation of basalt as an igneous rock (experiment
by James Hall)
 Deep pressure inside the earth affects chemical
reactions
 Subterranean heat produce basalt, granite and mineral
veins
The Present is the Key to the Past
Uniformitarianism- Charles Lyell (1830- Principles of Geology)
followed James Hutton (1795)
uniform rate of geologic processes
laws of nature do not change with time
Actualism- The Present is the Key to the Past
gradualistic and catastrophic events shape geologic processes
John Playfair (1802) “Amid all revolutions of the globe the
economy of nature has been uniform, and her laws are the only
thing that have resisted the general movement. The rivers and the
rocks, the seas, and the continents have been changed in all their
parts; but the laws which describe those changes, and the rules to
which they are subject, have remained virtually the same.”
Geology, A Historical Science
 Chemistry and physics controlled by
universal laws, independent of the time in
which they operate
 When geologist focus on present processes
they follow applied laws, but when they
focus on the past it is more historicalreconstruction of history based on biological,
chemical and physical laws
GEOLOGIC TIME
Time- the 4th dimension but unlike
the spatial dimensions, with time we
can only travel in one direction from
present to future
The pre-scientific period
 Before 1600 C.E. the Biblical account and
the speculations of the Greek philosophers
were accepted without great question
 Archbishop Ussher
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October 23, 4004 B.C.E. at 9AM
The era of speculative
cosmogonies
 From 1600-1700 C.E. a number of
comprehensive cosmogonies were proposed.
 These were long on armchair speculation
and short on substantive supporting
evidence.
 These cosmogonies were part of the new
emphasis of science in seeking rational
explanations of the features of the world
The disestablishment of Genesis
 From 1700-1780 C.E. period marked by a great deal of
field geology rather than grand cosmogonies.
 It became clear that there had been significant changes in
the Earth's topography over time and that these changes
could neither be accounted for by natural processes
operating during the brief, nor by the postulated
Noachian flood.
 Notable observations included:
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Studies of strata suggested that they were laid down by natural
processes in which the sea and land had changed places
several times. Studies of earthquakes and volcanoes showed
that the surface crust is subject to massive natural
transformation.
Observation of rain, wind, water erosion, and sea erosion in
action showed that they were forces capable of reducing
mountains and creating valleys.
The catastrophist-uniformitarian
debate: From about 1780-1850
 By the end of the 18th century it was clear that the Earth
had a long and varied history.
 Interest in major cosmogony was revived.
 The major debate was between the catastrophists, e.g.,
Cuvier, who held that the history of Earth was dominated
by major catastrophic revolutions and the uniformitarians,
e.g. Hutton and Lyell, who held that the history of Earth
was dominated by slow relatively uniform changes in an
Earth with a static over all history.
 During the early part of this period there was a
considerable amount of activity by scriptural geologists
who attempted to reconcile Genesis and geology.
The modern period: From 1850 to the
present
 The great debate was won by the
uniformitarians, so much so that the degree
of gradualism was overstated and the
importance of catastrophes was unduly
minimized.
 The modern period has been marked by an
enormous expansion of the detailed
knowledge of the geological history of the
Earth and the processes that have acted
during that history
Postulations on the age of the Earth
 In 1640 Ussher produced his famous calculation that
the Earth was created in 4004 BCE
 In the 1700's belief in a 6000 year old Earth
crumbled.
 Attempts to calculate the age of the Earth from
physical considerations yielded estimates that
ranged from 75,000 years (Buffon, 1774) to several
billion years (de Maillet, Buffon).
 By the early 1800's it was generally accepted that
the Earth had a long history. Its age, however, was
scarcely settled.
 The uniformatarians (Hutton 1788, Lyell 1830)
pictured the Earth as being indefinitely old
The Age of the Earth
 The catastrophists (Cuvier 1812, de Beaumont 1852,
Buckland 1836) accepted that the Earth was old; they
disagreed with the kind of change and the rate of change
that had occurred over that long history.
 There was no single estimate of the Earth's age in the mid
1800's and no good way to arrive at one.
 There were various attempts to estimate the Earth's age,
working back from sedimentation rates and other
geophysical phenomena. The attempts produced estimates
from about 100 million years up to several billion years.
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There were two major problems with such efforts. The first is
that the geological history was still being reconstructed.
The second is that the rates of the physical processes in
question are variable and knowledge of them was incomplete.
The Age of the Earth
 In 1862 Kelvin estimated the age of the Earth to be 98
million years, based on a model of the rate of cooling.
This was a minimum acceptable age consistent with
geology. Later in 1897 he revised his estimate downwards
to 20-40 million years.
 Kelvin did not know about radioactivity and heating of the
Earth's crust by radioactive decay; for this reason his
estimates were completely wrong. Likewise, it wasn't until
Einstein's theory of relativity was developed that there
was a good explanation of how the Sun could have been
shining as long as it had.
 The first radiometric dating was done in 1905; it and
subsequent measurements confirmed that the Earth was
several billion years old. Currently the best estimate of the
age of the Earth is 4.55 billion years
The Present is the Key to the Past
Uniformitarianism- James Hutton (1795)
uniform rate of geologic processes
laws of nature do not change with time
Actualism- The Present is the Key to the Past
gradualistic and catastrophic events shape geologic
processes
Geologic Time
Relative Time
Sequence of Geologic Events
Absolute Time- Radiometric Dating
Principles Used to Determine
Relative Age
 Cross-cutting RelationshipsAgricola/Lyell
 Truncated units (dikes and faults)
 Original Horizontality- Nicolas Steno
 Progressively younger from bottom => top
 Lateral Continuity-Steno
 Superposition-Steno
Principles Used to Determine
Relative Age
 Other Time Relationships
Contact Metamorphism
 Inclusions
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Correlation
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Physical Continuity of Lithologic Units
Similarity of Rock Types
Superposition
Correlation by Fossils
Principle of Faunal Succession
 Index Fossil
 Fossil Assemblage
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Time-Rock Units- rocks formed during a
particular time (lower, middle, upper)
Time Units- defined by distinctive changes in
fossils (Early, Middle, Late)
 Eonothem
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Erathem
• System- Rocks deposited during a particular period
– Series
» Stage
 Eons
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Eras- Major changes in life forms
• Periods
– Epochs
» Age
Geologic Time
 EON
Two or more geological eras form an Eon,
which is the largest division of geologic
time, lasting many hundreds of millions of
years
 ERA
Two or more geological periods comprise an
era, which is hundreds of millions of years in
duration
 PERIOD
The period is the basic unit of geological
time in which a single type of rock system is
formed, lasting tens of millions of years.
 EPOCH
An epoch is a division of a geologic period;
it is the smallest division of geologic time,
lasting several million years
 AGE
An age is a unit of geological time which is
distinguished by some feature (like an Ice
Age). An age is shorter than epoch, usually
lasting from a few million years to about a
hundred million years
Rock Units- necessary for geologic
mapping
 Group
 Formation- mappable rock unit,
similarity of lithology
•Member
–Bed
FORMATIONS
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Large enough to show on a map
Distinctive from neighboring rock units
Named after geographic locations
CONTACT
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Separation between 2 distinct rock units
Sedimentary contact
Other contacts
Unconformities
A) Angular Unconformity
B) Nonconformity
C) Disconformity
STRATIGRAHY
 The study of layers of sedimentary rocks
 The study of rocks--lithostratigraphy
 The study of fossil content--biostratigraphy
Correlation of Lower
Cambrian rock units in
western Montana
C, B, G and A are trilobite
index fossils
Sedimentary Facies developed in the sea adjacent to a land
area. Front face shows shifting of facies through time
Sedimentation during a regression: Coarsening
Upward Sequence
Walther’s Law- The vertical progression of facies will be
the same as the corresponding lateral facies change
A rise or fall in sea level will affect a far greater area along
a low coastline than along coastlines composed of highlands
that rise steeply adjacent to the sea
The Vail sea-level
Curve: Changes in
Global sea-level
through time
Standard Geologic Time Scale
 Established in the 19th century- Developed by J.
Phillips 1840 based on work by Sedgwick & Murchinson
 Based on Fossil Assemblages
 Eons, Eras, Periods, and Epochs
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PHANEROZOIC since 544 m.y.b.p.
• Paleozoic Era 544-245 m.y.b.p.
• Mesozoic Era 245-65 m.y.b.p.
• Cenozoic Era 65 m.y.b.p.-present
– Tertiary & Quaternary Periods
» Recent (Holocene) Epoch last 10,000 years
 Precambrian- All time before Paleozoic
http://www.athro.com/geo/timecalc.html