Transcript Earth History GEOL 2110 Lectures 3 & 4 Development of Geological Concepts Major Concepts • In the 17th and 18th centuries (Age of Reason), application of.

Earth History
GEOL 2110
Lectures 3 & 4
Development of
Geological Concepts
Major Concepts
• In the 17th and 18th centuries (Age of Reason), application
of the scientific method of observation and interpretation
began with the purpose of understanding earth processes
in the context of the biblical account, but wound up
challenging and discrediting that explanation.
• Recognition of stratigraphic principles allowed for the
interpretation of time in sedimentary rocks
• Recognition of the changes in fossil assemblages with time
provide a power tool for correlation
• Recognition that the earth is dynamic and constantly
reshaping and recycling itself required “great drafts upon
the bank of antiquity”
• Recognition that processes happening on earth today likely
have happened throughout most of geological time
provided a powerful intellectual tool to understand the
history of the earth
Earth History based on Genesis
With humans being cast out of Paradise, punishment was
meted out by throwing the earth into chaos. This brought on:
volcanism uplift and scaring of the land violent weather
The Great Flood – Diluvialists
A scholarly study of the geneaology of the Bible led Anglican
Archbishop Ussher in 1654 to conclude that the Earth was
created on October 23, 4004 B.C. Another determined the 40day flood began November 18, 2349 B.C.
In the 17th and 18th centuries (Age of Enlightenment/Reason)
intellectuals began to promote scientific inquiry, skepticism
and intellectual interchange and challenged ideas grounded in
tradition and faith.
Early Ideas on Fossils
• Some early Greek and Roman philosophers saw them as
remains of past life forms; large bones came from a former
race of giants
• Aristotle (384-322 BC) suggested that they represented failed
attempts of the seeds of life that sprang from rock and mud
• Middle Ages (500-1450) fossils were variously regarded as
works of the devil, Gods handiwork, formed by mysterious
“molding forces” in rocks, or sports of nature.
• Chinese thought vertebrate fossils were the remains of
dragons
• Most common interpretation in the west was that they were
the remains of animals and humans who had perished in the
Deluge.
Leonardo – the Heretic
1452-1519
• Interpreted marine fossils in
the high Alps to be remains of
ancient life forms
• Noted fossil types and
concentrations varied from
layer to layer – fossils must be
same age as host rocks
• 40 days was not enough time
for marine organisms to travel
to the high Alps during the
flood
• Many fossils are to delicate
to have been transported
during the flood
Nicholas Steno
1638-1686
• Danish geologist, anatomist,
theologian
• In 1669, he published "The
Prodromus of Nicolaus Steno's
Dissertation Concerning a Solid Body
Enclosed by Process of Nature Within
a Solid” summarizing his ideas on
stratification and fossils in rocks and,
most significantly, the implications
for TIME.
• In 1665, he converted to Roman
Catholicism, whereupon his interest
in scientific inquiry waned
• Became a priest in 1675) and a
bishop in 1677)
Saw similarity
of fossil sharks
teeth with
modern teeth
Steno’s Stratigraphic Principles
Superposition – successively
higher sedimentary layers are
successively younger
Original Horizontality – All
sediments are deposited
horizontally; tilted strata are
thus disturbed from their
original state
Lateral Continuity – Strata
originally extended in all
directions to the edges of
their basins of deposition
Robert Hooke
1635-1703
• British naturalist, architect,
polymath
• Concluded that fossilized objects
were the remains of living things
that had been petrified by being
soaked in mineral-laden water
• Believed that fossils provided
reliable clues to the past history of
life on earth, and that they might
represent species that had become
extinct through some geological
disaster and thereby provide
useful time markers
• His ideas were not popularized in
part because of his "cantankerous,
envious, vengeful“ personality
Ammonite fossil sketches by Hooke, 1703
Fossils As Time Markers
Evidence of Evolution and Extinction
• With the systematic mapping of
geologic strata in the late 1700’s,
it became evident that particular
stratigraphic units contain a
unique assemblages of fossils
• It was also recognized that within
a stratigraphic (i.e. time) section,
a particular fossil type had a
point of appearance and
disappearance
• This brought concepts of
biological evolution and
extinctions to greater acceptance
and the surrender of the notion
of a diluvian origin to fossils
Early Biostratigraphic Mapping
John Woodward (1723) first to note a similarity of
marine fossils between
Britain and France chalk
units
Guettard and Lavoisier
(1746) – first geologic map
showing that correlation
William Smith
1769-1836
• Son of a blacksmith, canal
surveyor
• From 1791-1812, he
meticulously mapped the
distribution of strata in
England and documented
their fossil assemblages
• In 1815, published “The Map
that Changed the World”
• Simon Winchester’s 2001
book is a great read about
the trials and tribulations
encountered by the
commoner Smith
Smith’s Biostratigraphy
“wonderful order and regularity with which nature has disposed of these singular
productions (fossils) and assigned to each its class and peculiar Stratum” (W. Smith, 1796)
Fossil Assemblages
Lithologic Units
Cuvier and Brongnairt
Biostratigrapy of the Paris Basin (1811-1822)
Geologic Correlation between
Paris and London (1722)
Principle of Fossil Correlation
Like assemblages of fossils are of like age and therefore
the strata containing them are also of like age
Index Fossils
Characteristics:
• easily recognized
(unique characteristics)
• Common to many
geological
environments
• restricted to a very
limited thickness of
strata (i.e., time)
Earth History
GEOL 2110
Lectures 3 & 4
Development of
Geological Concepts
Part II
Toward a Unified Theory of the Earth
The Cosmogonists
Developed all-encompassing and largely speculative theories
of the origin of the cosmos that were no longer tied to
scripture, but based on observations of nature and emerging
ideas about physics;
Rene Descartes (1596-1650)
“I think, therefore I am”
The era of speculative cosmogonies ran
from AD 1600-1700. In this period 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.
Toward a Unified Theory of the Earth
The Cosmogonists
G.L. Buffon – 1749 Histoire Naturelle – 34 volume treatise on the
origin of earth and the cosmos. Speculated that the planets were
created by the impact of a large comet with the sun (influenced by
Halley’s comet drive-by in 1682 and its predicted return in 1758.
George Louis Leclerc,
Comte de Buffon
• Estimated the Earth to be 75,000 years
old based on its cooling from an
originally molten state
• Envisioned 7 epochs of earth formation
of core, hydrosphere, atmosphere and
crustal layers
• Rejected the literal interpretation of
scripture as a source of geological
insight
Toward a Unified Theory of the Earth
The Neptunists
A.G. Werner (1787) - Developed a chronostratigraphy of the
Earth’s crust that was based on progressive deposition of rocks
from a gradually subsiding ocean. The theory was nearly
universally accepted in the late 1700’s. Defined five crustal units:
Primitive Series – crystalline rocks considered to be the first
precipitates from the ocean before the emergence of land.
Transition Series - more indurated sedimentary sequences that
were the first orderly deposits from the ocean.
Secondary Series - the remaining, obviously stratified fossiliferous
rocks and certain associated "trap" rocks. These were thought to
represent the emergence of mountains from beneath the ocean
and were formed from the resulting products of erosion deposited
on their flanks.
Alluvial Series - poorly consolidated sands, gravels and clays
formed by the withdrawal of the oceans from the continents.
Volcanic Series - younger lavas flows demonstrably associated with
Abraham Gottlob Werner volcanic vents. Werner believed that these rocks reflected the local
1749-1817
effects of burning coal beds.
Toward a Unified Theory of the Earth
The Neptunists
Interesting Interpretations:
- Primitive granites, highly metamorphosed rocks, basalts flows and
diabase dikes are crystalline precipitates from the universal ocean
- Mountains reflect the original chaotic landscape of the earth; they
are static, fixed in space and time
- Volcanoes are minor, geologically unimportant elements of the
crust created by the subterranean combustion of coals seams.
Toward a Unified Theory of the Earth
The Vulcanists
Auvergne Volcanoes , S. France
Early Challenges to Werner’s theory:
- Where did the water go???
- The Auvergne volcanoes rest on granite (primitive rocks)!
- Italian and French scientist showed that “trap rock” interlayered with
sedimentary rocks were identical to recent basalt flows and thus
were formed from molten lava and were not precipitates from
seawater.
Toward a Unified Theory of the Earth
The Plutonists
James Hutton (1726-1797) – The Father of Modern Geology
A member of the Edinburgh Oyster Club that included economist Adam Smith,
mathematician John Playfair, philosopher John Hume, and chemist Joseph Black
1788. Theory of the Earth; or an investigation of the laws observable in the composition,
dissolution, and restoration of land upon the Globe.
Principal Concepts
• The current landscape is a balance
between rejuvenation (uplift) and
destruction (erosion) of the earth’s surface
• The earth is eternally dynamic and everchanging (“No Vestige of a Beginning, No
Prospect of an End”)
• The internal heat of the earth is
responsible for uplift of mountains and
the igneous origin of granite and basalt
Toward a Unified Theory of the Earth
The Plutonists
Angular Unconformity at Siccar Point, Scotland
Angular Unconformity at River Jed, Scotland
“The mind seemed to grow giddy looking so far into the
abyss of time”
John Playfair (1802)
Illustrations of the Huttonian Theory of the Earth
Toward a Unified Theory of the Earth
The Uniformitarianists
Charles Lyell (1797-1875) – Railed against catastrophism and instead
argued that the Earth is in a steady-state equilibrium with uniformity in
the rates and types of processes over all geological time.
12 Editions 1830-1875
Toward a Unified Theory of the Earth
The Uniformitarianists
Frontpiece Illustration from Principles of Geology (1857)
Toward a Unified Theory of the Earth
The Evolutionists
Charles Darwin (1809-1882) - The directionalism inherent in
biological evolution went against the basic notion of static
equilibrium that Darwin’s friend and colleague Lyell advocated.
On the Origin of Species
1859
Introduced the scientific
theory that populations
evolve over the course
of generations through
a process of natural
selection.
Toward a Unified Theory of the Earth
The Physicists
Sir William Thompson (The Lord Kelvin) (1824-1907) - Renown
physicist of the late 19th century best known for determining the
value of absolute zero temperature and for estimating the age of the
earth based on principles of thermodynamics applied to an initially
molten globe – his estimates ranged from 400 million to 20 million.
Kelvin thought Lyell’s notion of
perpetual equilibrium was totally
implausible based on the principles of
physics applied to a cooling earth.
Toward a Unified Theory of the Earth
The Actualists
Today, earth scientist recognize that:
• the basic principles of nature are uniform
through geological time
• rates and scales of geological processes and
events can change over time and be nonlinear
• some changes are cyclical, some are
unidirectional and irreversible
• the simplest explanation is the best, unless data
suggest otherwise
• In the context of actualism, present-day
processes can be useful analogs to the geologic
past
Why is Actualism Important?
Geology strive to establish not only the
present condition of the Earth, but also
the past and the future. The principles
of Actualism provide us with guiding
principles about how to read the
chapters of the Earth’s past.
Not only is the present the key to the
past, but the reverse is true as well.
Next Lecture
EVOLUTION