Transcript Development of Geological Concepts I

Earth History
GEOL 2110
Lecture 3
Development of
Geological Concepts, Part I
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 temporal 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 genealogy 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 too 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)
Next Lecture
Development of
Geological Concepts
Part 2