Earth History GEOL 2110 Lectures 3 & 4 Development of Geological Concepts.

Earth History GEOL 2110

Lectures 3 & 4Development 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 GenesisWith 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 40-day 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 Heretic1452-1519

• 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 Steno1638-1686

• 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 PrinciplesSuperposition – 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 Hooke1635-1703

• 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 MarkersEvidence 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 Smith1769-1836

• 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

Fossil Assemblages Lithologic Units

“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)

Cuvier and BrongnairtBiostratigrapy of the Paris Basin (1811-1822)

Geologic Correlation between Paris and London (1722)

Principle of Fossil CorrelationLike 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 & 4Development of

Geological ConceptsPart II

Toward a Unified Theory of the EarthThe 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;

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. Rene Descartes (1596-1650)

“I think, therefore I am”

Toward a Unified Theory of the EarthThe 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.

• 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 insightGeorge Louis Leclerc,

Comte de Buffon

Toward a Unified Theory of the EarthThe 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:

Abraham Gottlob Werner1749-1817

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 volcanic vents. Werner believed that these rocks reflected the local effects of burning coal beds.

Toward a Unified Theory of the EarthThe 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 EarthThe Vulcanists

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.

Auvergne Volcanoes , S. France

Toward a Unified Theory of the EarthThe Plutonists

James Hutton (1726-1797) – The Father of Modern GeologyA member of the Edinburgh Oyster Club that included economist Adam Smith, mathematician John Playfair, philosopher John Hume, and chemist Joseph Black1788. 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 ever-changing (“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 EarthThe Plutonists

Angular Unconformity at River Jed, Scotland

Angular Unconformity at Siccar Point, 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 EarthThe 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 EarthThe Uniformitarianists

Frontpiece Illustration from Principles of Geology (1857)

Toward a Unified Theory of the EarthThe 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 Species1859

Introduced the scientific theory that populations evolve over the course of generations through a process of natural selection.

Toward a Unified Theory of the EarthThe 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 EarthThe 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