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Transcript
History of the Discipline:
Geology & Paleontgology
Nicolaus Steno (Danish, 1638-1687)
Nicolas Steno – Danish anatomist and scientist, discovered three major
principles of geology: Law of Superposition, Principle of Original Horizontality,
and the Law of Lateral Continuity. Steno also showed convincingly that fossils
were the remains of once living organisms.
Law of Superposition - in an undeformed sequence of
sedimentary rocks each bed is older than the one above and
younger than the bed below.
Principle of Original Horizontality - layers of sediment are
generally deposited in a horizontal position. Folding and inclination
occur after deposition.
Law of Lateral Continuity - layers of sediment initially extend laterally in all directions
(laterally continuous). Rocks that are otherwise similar, but now separated by a valley or
other erosional feature, can be assumed to be originally continuous. In reality layers of
sediment do not extend indefinitely - limits can be recognized and are controlled by the
amount and type of sediment available and the size and shape of the sedimentary basin.
Giovanni Arduino (Italian, 1713-1795)
Classified mountains according to rock type
Tertiary – gravel, sand and clay beds
alluvium
Secondary – layered rocks containing fossils
sedimentary
Primary – crystalline rocks are the oldest
igneous and metamorphic
Abraham Werner (German, 1749-1817)
Werner devised a new system of classification
based on his idea of Neptunism.
All rocks were deposited or precipitated from an
single universal ocean that covered the earth.
Neptunism: all rocks are marine in origin
Alluvium – gravel, sand and clay bed
Arduino’s Tertiary Mountains
Sandstones, shales, coal beds &lava flows
Transition rocks– ocean cools and deepens,
these rocks contain fossils
Arduino’s Secondary Mountains
Primitive rocks – formed first from original
ocean filled with dissolved minerals
Arduino’s Primary Mountains
Problems with Neptunism
1. Where did all the water from the vast ocean
go?
2. How were lava flows deposited in an ocean?
Thus enters a new idea…
Plutonism - the primitive rocks
originated from heat (or fire),
and formed underground rather
than in oceans.
James Hutton (Scottish, 1726-1797)
Sicar Point, Scotland - first described by James Hutton
200 years ago.
Lawyer, doctor, scientist, and “gentleman farmer” is often considered to be the
father of modern geology. Proponent of a dynamic, cyclic concept of Earth
history. Champion of the Plutonist theory that challenged Werner’s
concepts. Three major contributions that form the basis of geology.
Principle of uniformitarianism
(actualism)
Hutton explains that the present is the key to the past
• The earth is dynamic, so as rocks are eroded and
weathered, so are there new rocks are created.
• Therefore, the geologic process observe today were
at work in the past… even the distant past.
HOWEVER – those processes may have happened at
different rates or with different intensity than they
do now.
Significance of Unconformities
Siccar Point provided Hutton
with insight into the pattern
and process of sedimentary
deposition. Formulated the
idea of conformable versus
unconformable strata.
Conformable - layers of rock that have been deposited without
interruption.
Unconformity - represents a long period where deposition
ceased, erosion removed previously deposited rocks, and then
deposition resumed. In each case uplift and erosion are
followed by subsidence and sedimentation.
Ultimately Hutton
realized unconformities
represented “a break
in time”.
Disconformity
Disconformity - type
of unconformity in
which the beds above
and below are parallel.
Most common.
Angular Unconformity
Angular Unconformity tilted or folded
sedimentary rocks that are
overlain by younger, more
flat lying strata. Easiest
recognized.
Nonconformity
Nonconformity - separates
older metamorphic or
intrusive igneous rocks from
younger sedimentary strata.
William Smith (English, 1769 – 1839)
William Smith – English canal builder. Understood stratigraphy, and
used the principle to create the first geologic map of England in
1815.
William “Strata” Smith formulated three
important principles in historical geology:
1. Principle of fossil succession - Older fossils in lower
rocks, younger fossils in upper rocks.
2. Principle of biostratigraphic correlation - rocks
containing same fossils formed at the same time
3. Index Fossils provide two kinds of information:
•
•
Whether species existed at same time
The order in which species existed
Principle of fossil succession:
Fossil organisms succeed one another in a definite and determinable order,
and therefore any time period can be recognized by its fossil content.
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Fossil succession of horses
Major changes: number of toes decreases as
teeth become more complex
Index Fossils:
• short existence in time • distinctive anatomy
• abundant as fossils
• wide distribution geographically
Microfossils provide the best temporal resolution
and make ideal index fossils
Spores
Diatoms
Pollen
Radiolarians
Foraminifera
Dinoflagellates
Principle of Biostratigraphic Correlation
Using the Principle of Fossil Succession and Index Fossils to
correlate strata over large distances
Biostratigraphic Correlation
Rock columns can be correlated using fossils
George Cuvier (French, 1769-1832)
• A well respected anatomist and
paleontologist who validated
Smith's observations on fossil
succession.
• Developed the idea of
catastrophism - the stratigraphic
record is punctuated by
unconformities. These
unconformities represent
periods of global catastrophic
events in which all life on Earth
was wiped out (ie: Noah’s Flood).
Opposing view of uniformitarianism.
Charles Lyell (English, 1797-1875)
Authored Principles of Geology (1830)
• Expounded on Hutton’s principles of cross-cutting relationships
• Developed concept of relative age dating and sequence of
events
Principle of Cross-cutting Relationships
When faults or magma intrudes, we assume fault or
intrusion is younger than the rocks affected.
Cross-Cutting Relationship: Dike
Cross Cutting: Granitic Intrusion
Can apply to structures as well – faulting & unconformities
Charles Darwin (English, 1809-1882)
• Developed a general theory of
evolution to account for fossil
succession; proposed natural
selection as the mechanism for
evolution.
• Recognized that fossils recorded
the evolution and extinction of life
• Reviewed the work of Wallace,
who had similar findings on
natural selection.
• Published Origin of Species (1859)
Voyage of the Beagle
Darwin’s 5 year trip around the globe on the H.M.S. Beagle
(1831-1836) gave him the opportunity to OBSERVE many
different types of animals. Observations led to a
hypothesis… natural selection.
Louis Agassiz (Swiss, 1807-1873)
• First to propose that immense
ice sheets once covered North
America (1840), including an
the “Ice Age,” which ended
about 8,000 to 10,000 years
ago
• Studied glacial features, like
striations, erratics, and
moraines
Vertebrate paleontologist; moved to • Controversy…
U.S. in 1846; Harvard professor
The Bone Wars
Othniel C. Marsh (US, 1831-1899)
• Professor of paleontology at
Yale
• Founded Peabody Museum
of Natural History
• Led famous dinosaur
explorations of the western
U.S. Well… not really led,
but rather paid others to
undertake explorations.
Edwin D. Cope (US, 1850-1897)
• Associated with the Academy
of Natural Sciences in
Philadelphia and the
American Museum of Natural
History
• Led famous dinosaur
explorations of the western
U.S. Actually spent a great
deal of time in the field
himself.