Earth History GEOL 2110

Lecture 3Development 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 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 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 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 too 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)

Next Lecture

Development of Geological Concepts

Part 2