The Age of EnlightenmentLate 18th centuryTremendous advances in science, politics, philosophy, economics, etc.Thomas Jefferson – an American member of the Enlightenment

The Scientific Method

Inductive phase : reasoning from the specific to the general(Formulate the hypothesis) deductive phase: reasoning from the general to the specific(test the hypothesis)

Example: formulation of the hypothesis of spontaneous generation; Its testing by Louis Pasteur

Hypothesis:

An explanation that accounts for a set of observations and can be tested by further investigation

Observation v.s. fact

A fact is a “cooked” observation

Lawyers talk about “facts”

Scientist are more conservative- talk only about observations

Theory

A system of ideas used to explain observations

Paradigm

A shared perspective within a scientific communityUsually expresses as a set of related theories

James Hutton

A “gentleman farmer”Associate of James Watt and other members of the “Oyster Club”The Scottish Enlightenment – centered in Edinburgh(home of Hume, Smith)

Hutton and DeismHutton was a DeistDeism held that one could gain greater understanding of God by understanding nature – his creationThe “Denudation Dilemma - a theological conundrum

Denudation DilemmaRock and soil are essential to lifeRock is the foundation for where we liveSoil is the foundation of agriculture – sustains lifeTo the Deists, this was evidence of God’s beneficence

Denudation DilemmaRocks decay at Earth’s surface – weathering

Soil is washed away from farmlands – erosion

Weathering and erosion indicate destruction of the landMartin Luther predicted that the world would end as a result of erosion

The DilemmaHow can one reconcile God’s beneficence with the destruction of the land, which is essential for life?

Hutton’s ObservationsProcesses of weathering and erosion are slowMany rocks visible on the land are made up of the products of weathering and erosionThese rocks are Sedimentary Rocks

Sediments accumulate in the ocean, so these rocks originally formed in the ocean

The RiddleHow can rocks that formed below sea level be found on land?

More of Hutton’s ObservationsNot all rocks form by accumulation of sedimentSome rocks are made of crystalsThese rocks show signs of having formed at very high temperatures from molten materialThese are Igneous Rocks

Arthur’s Seat and Salisbury Crags

Hutton’s SolutionIgneous rocks provide evidence for heat within the EarthHeat is capable of work (Watt’s influence)Heat within the Earth lifts rocks from the sea and creates new landThe dilemma is solved because as erosion destroys land, heat uplifts new land

Implications of Hutton’s SolutionEarth processes are slowGreat changes can be accomplished with great amounts of timeEvidence of great expanses of time recorded by the rocksConclusion: the Earth must be extremely old

Evidence for Deep Time – Hutton’s Unconformity

Sedimentary Rocks reflect change in environment on the Earth’s surface.

Rises and falls in sea levelClimateChange in life forms

UNCONFORMITIES

Angular Unconformitya) deposit of sedimentsb) tectonic event c) erosiond) deposition

Historical Geology

Founders of Historical GeologyNicolaus Steno (1638-1687)

fossil descriptions

first stratigrapher

Steno's Laws

Superposition

Original Horizontality

Original Lateral Continuity

Historical Geology

Steno's LawsSuperposition

Why the law of superposition is necessary- overturned strata in the hamalayas

Steno's LawsOriginal Horizontality

Steno’s Laws: original Horizontality

Steeply dipping sandstone and shale in the Oachita Mountains, Arkansas

Original Continuity Steno’s law of

Neptunism vs. Plutonism

Neptunism

Plutonism

the theory that the rocks of the Earth's crust all consist of material deposited from,or crystallized out of the ocean. Abraham Gottlob Werner (1749-1817)

the concept of the formation of crystalline rocks by solidification from a melt.James Hutton (1726-1797)

Founders of Historical GeologyJames Hutton (1726-1797)

dynamic/cyclic concept of Earth history- “no vestige of a beginning, no prospect of an end”

recognized significance of unconformities

deep timeUniformitarianism:

“ The present is the key to the past”

Hutton’s “Great unconformity” at Siccar point, eastern Scotland

Hutton’s “Great unconformity”

at Siccar point, eastern Scotland

Historical Geology

Founders of Historical GeologyCatastrophism vs. Uniformitarianism

catastrophism

uniformitarianism

the doctrine that sudden violent, short-lived, moreor less worldwide events outside our present experience or knowledge have greatly modified the Earth's crust accounting for its present configuration as well as for the observed distribution of life formsJames Ussher (1581-1656)

the fundamental principle that geological processes and natural laws now operating to modify the Earth's crust have acted in much the same manner and with essentially the same intensity throughout geologic time, and that past geologic events can be explained by forces observable today; "The present is the key to the past."James Hutton (1726-1797)

Uniformitarianism: The present is the key to the past(Hutton, 1788)

The basic physical, chemical and biologicallaws of the present-day world also operated in the Earth’s past.

Implications: 1. Present day geological processes acting at slow

rates, but over long time periods, can produce dramatic results.

2. Based on the study of changes that are known to occur gradually (e.g. wearing down of mountains),the Earth must be very old.

Misconception:All geologic processes are slow and gradual.

Historical Geology

Founders of Historical GeologyWilliam Smith (1769-1839)

first geologic map

Principle of Faunal Succession

Historical Geology

Founders of Historical GeologyCharles Lyell (1797-1875)

first geologic time scale

relative time

Principle of Cross-cutting Relationships

Principle of Inclusions

Historical Geology

Lyell's Principles of Relative TimeCross-cutting Relationships

Nonconformity Unconformity separating younger rocks from distinctly

older, metamorphosed rocksa) tectonic event produces some sort of crystalline

rockb) uplift with erosionc) deposition

Disconformity

Unconformity in which beds on opposite sides are parallel

a) depositionb) erosionc) deposition

Paraconformity DepositionErosionDeposition

Uniformitarianism the laws of nature do not change with time.Hutton- first to discover geological time, and the first to state that the Earth is much older than 6000 years.Before Hutton, everyone believed in catastrophism, which states that the shape of the Earth came to be quickly and violently. Catastrophism was a by-product of the fact that religion was in control of most governments.

An old EarthRecycling of Earth materialsEvidence for earlier episodes of recycling“No vestige of a beginning… no prospect of an end.”

Hutton’s “Theory of the Earth” - 1785

Playfair’s Commentary“The mind seemed to grow giddy looking so far into the abyss of time…”

Example of Slow Change: Green River, Utah

1871

1968

Catastrophism: Changes in the Earth are sudden and violent

Major changes in the Earth’s state tend to occur in short bursts of activity.

Implication: Geologic changes tend to occur as rare events that are short-lived with little change occurring betweenthese events.

Misconceptions:1. All changes that occur on the Earth are catastrophic2. The Earth and its present day features were produced

during a single event, and therefore the Earth must be very young

Catastrophic Event: Eruption of Mount Vesuvius, Italy, 79 AD

Effects: Mass human mortality in Pompeii and Herculaneum

volcanicashlayerexcavated ruins

Catastrophic Event: Chicxulub Crater, Yucutan, Mexico

Impact event: 65 million years agoCrater size: 180-280 km dia.Profoundly affected global climate due to atmospheric dustPossible cause of mass extinction

What’s so remarkable about Hutton’s Ideas?

Contrary to prevailing views of the timeBased on observation – what he sawHutton drew inferences from his observationsInferences are hypotheses

Hypotheses are testable

This is an application of the scientific method to study of the Earth