History of Geologic Thought

History ofGeologic Thought

Historical Geology – Principles

History of Geologic Thought


Myths and Legendsto explain the “unknown”

Creation: every society has a creation myth.

Geologic processes:earthquakes, volcanoes,




Fossils: what are they?

• really organic remains?• how - when did they get there?

• before/after rock formed?





• animals crawled into cracks • remains of a lost race

• grew from seeds, solution or vapors• "figure stones" by "plastic forces"





• animals crawled into cracks • remains of a lost race

• grew from seeds, solution or vapors• "figure stones" by "plastic forces"

Fossil Folklore @ Natural History Museum, London

http://www.nhm.ac.uk/nature-online/earth/fossils/fossil-folklore/myth_themes.htm





• Organisms caught in the Biblical deluge

• dominated scientific thought up to mid-19th Century



Scientific Observation:

Leonardo da Vinci: 1500's

Recognized that fossil shells represent ancient marine life, even though they were miles from the nearest shore.

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Scientific Observation:

Rationale

• too fragile to be transported for miles • fossil communities,not jumbled

• distinct fossiliferous layers, multiple events

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da Vinci Geologist @ UCMP

http://www.ucmp.berkeley.edu/history/vinci.html



Fundamental Stratigraphic Principles


Nicolas Steno:

• 1600’s

• Physician - "amateur scientist"

• Observed sediment and water sorting, and stratification

Steno as Geologist - Theologian

http://academic.emporia.edu/aberjame/histgeol/steno/steno.htm

http://dlibrary.acu.edu.au/research/theology/ejournal/aejt_5/Sobiech.htm



1. Superposition:

in a sequence of undisturbed strata,

oldest layers are on the bottom,

youngest on top.


1. Superposition:



2. Original horizontality:

Particles settle from

a fluid under the

influence of gravity

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Layers must therefore be

parallel and horizontal to

the surface on which particles settle.




uplifted, butundisturbed beds

Grand Canyon



some tectonic eventtilted these beds


old on the bottom?



some tectonic eventtilted these beds


Maybeold on the bottom?



3. Original lateral continuity:

Strata originally extend in all directions until they:

• thin to zero at edge of basin

• end abruptly against some barrier




Strata originally extend in all directions until they:

• change gradationally into some different kind of sediment.

“Old” View of the World


Catastrophism:

The belief that geologic features can be

explained by catastrophic events (floods)

on a scale not seen today.



Catastrophism:

The belief that geologic features can be

explained by catastrophic events (floods)

on a scale not seen today.

Especially the Noachian, Biblical Flood



Catastrophism:

Indirectly linked to interpretation

of a young Earth.

< 10,000 years old

“New” View of the World


4. Uniformitarianism:

Uni - form - i - tarian - ism



4. Uniformitarianism: Uni - form - i - tarian - ism

James Hutton:

"The past history of our globe can be

explained by what can be seen to happen now"

Hutton Bio @

http://www-gap.cs.st-and.ac.uk/~history/Biographies/Hutton_James.html



4. Uniformitarianism: Uni - form - i - tarian - ism

"The present is key to the past"

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Present Day Beach with forming Ripple Marks

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Uniformitarianism

Lava Beds National ParkNew Mexico

500,000 yrs old

Hawaiian Volcano

http://www.nps.gov/labe/



Strict uniformitarianism: what we see today ...

is exactly the conditions of the past



Actualism:

"Laws of nature" are inviolable:

gravity, properties of water, chemical reactions

20th C



Actualism:

But, we now recognize thatintensity and rates may vary:

• climate change • tectonic spreading rates • intensity of volcanism



Actualism:

• the stray meteor



With Actualism:

We can account for events that

have not occurred over the course

of human time span.

Deep Geologic Time


Hutton: Siccar Point Scotland Recognized significance ofan unconformities.

Deep Geologic Time


Hutton: Siccar Point Scotland Recognized the significance

of unconformities.

Deep Geologic Time


Hutton: Siccar Point Scotland

Deep Geologic Time


Hutton: • developed a cyclic view of the earth

• earth in a continuous state of fluxold rocks decay,new rocks form (dynamic)

Deep Geologic Time


Hutton:

• Did not see the need to

invoke catastrophes to explain

geologic formations.

Deep Geologic Time


Hutton:

• Did not see the need to

invoke catastrophes to explain

geologic formations.

• Observable processes and

... Time

Deep Geologic Time


History of Geologic Thought

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