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Lecture 12

01:460:100 Lecture Notes - Lecture 12: Deep Time, James Hutton, MudcrackPremium

Geological Sciences
Course Code
Mark Feigenson

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Lecture 12
Chapter 12 - Deep Time: How Old Is Old?
Geologic time - Discovering the magnitude of the Earth’s past was a momentous
discovery in the history of humanity. This discovery forever altered our perception of
ourselves within nature and the Universe.
Understanding time permits assigning an age to…
Geologic structures.
Tectonic events
Deep time – The immense span of geologic time.
It is so vast that it is difficult for people to grasp.
Human history is tiny compared to geologic time.
Scientists began to find clues to an ancient Earth.
Nicolaus Steno (1638–1686) – Danish physician.
Observed marine fossils high in the Apennines.
Deduced that these were ancient animals in loose sediment.
Lithification and uplift suggested long periods of time
James Hutton (1726-1797) – Scottish physician.
Called “the Father of Modern Geology.”
First to articulate the “Principle of Uniformitarianism.”
Of the abyss of time, Hutton wrote: “we find no vestige of a beginning; no
prospect of an end.”
Principle of Uniformitarianism - “The present is the key to the past.” Processes
seen today are the same as those of the past.
Ancient mud cracks formed as mudcracks do today. Geologic change is
slow; large changes require large times
There are two ways of dating geological materials.
Relative ages – Based upon order of formation - assign order to events
Qualitative method developed 100s of years ago. Permit determination of
older vs. younger relationships.
Logical tools are useful for defining relative age: Principle of
uniformitarianism, Principle of superposition, Principle of original
horizontality, Principle of original continuity, Principle of cross-cutting
relationships, Principle of inclusions, Principle of baked contacts
Numerical ages – Actual number of years since an event.
Quantitative method developed recently. Age is given a number. Assign
exact dates to events
Uniformitarianism – The present is key to the past. Physical processes that we
observe today operated in the same way in the geological past. Modern
processes help us understand ancient events.  
Superposition - In an undeformed sequence of layered rocks…
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