Transcript Development of Geological Concepts II

Earth History
GEOL 2110
Lecture 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; reinforced by melting
experiments of Hall (1792)
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 Catastrophists
From the their biostratigraphic mapping
in the Paris Basin, Cuvier and Brongniart
interpreted the many mass extinctions,
dramatic changes in rock type, and
obvious unconformities found in the
Paris Basin sedimentary sequence as
evidence that the earth experience
repeated catastrophic revolutions
between periods of relative quiescence.
Cuvier believed that all life was present
at the beginning and that selective
preservation and extinctions gave rise to
present day life forms.
Cuvier's (1812) section for the Paris Basin.
Toward a Unified Theory of the Earth
The Uniformitarians
Charles Lyell (1797-1875) – Railed against catastrophism and instead
argued that the Earth is in a steady-state equilibrium with uniformity in
the types and rates of processes over all geological time - Gradualism
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 (glaciation), some are
unidirectional (growth of continents) and irreversible
(oxygenation of the atmosphere, evolution)
• 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