principles of geology - ccsf home pagegeology, the principles of geology (1830) –traveled widely...
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Principles of
Geology
UNIFORMITARIANISM
James Hutton (1726-1797) – Made observations on his
land of unconformities – Traveled to other parts of
Europe to observe glaciation and other processes
– Published Theory of the Earth, which introduced the idea of uniformity
– Also gave us the “Rock Cycle” and “Ice Ages”
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THEORY of the EARTH; or an INVESTIGATION of the Laws observable in
the Composition, Dissolution, and Restoration of Land upon the Globe. By JAMES HUTTON, M.D. F.R.S. EDIN. and
Member of the Royal Academy of Agriculture at Paris
UNIFORMITARIANISM
The geologic past can be interpreted and explained by referring to present day processes, given enough time.
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UNIFORMITARIANISM
“The present is the key to the past”
UNIFORMITARIANISM
Natural laws don’t change with time
F=ma
D=rt
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UNIFORMITARIANISM
It is not necessary to invoke catastrophes or the supernatural to explain the rock record of the past
Georges Cuvier The Deluge
UNIFORMITARIANISM
Charles Lyell (1797-1875) – Popularized Hutton’s
ideas in a “textbook” of Geology, The Principles of Geology (1830)
– Traveled widely and made many geologic observations including rise and lowering of sea level in the past
– Greatly influenced Charles Darwin.
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PRINCIPLE OF SUPERPOSITION
PRINCIPLE OF ORIGINAL
HORIZONTALITY
Nicolaus Steno (1638-1686)
– Observed layered rocks tilted and folded in the Alps
– Observed fossils in the rocks, suggesting they were once marine deposits
– Published a paper indicating original horizontality and superposition
Fossils
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PRINCIPLE OF SUPERPOSITION
Rocks are hardened layers of sediment once laid down under water (Sedimentary rocks only).
Layers of rock were laid down sequentially, oldest at the bottom.
In an undisturbed sequence of layered rock, the oldest layer is at the bottom and the youngest at the top.
PRINCIPLE OF ORIGINAL
HORIZONTALITY
Sedimentary rock layers form from sediment laid down under water.
Sediment is laid down under water essentially horizontally.
Rock layers were originally laid down horizontally.
Any tilting or folding of rock layers indicates they have been moved from their original horizontal position.
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Original Horizontality
Swiss Alps
PRINCIPLE OF FAUNAL
SUCCESSION William Smith (1769-
1839)
– Created first geologic map
– Discovered fossils varied systematically in rock layers
– Fossils indicated the order of the rock layers as well as identifying them
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First Geologic Map
By
William Smith
Each color represents a unit of rock of a certain type and with characteristic fossils in it.
PRINCIPLE OF FAUNAL
SUCCESSION
Fossils occur in an orderly sequence such that a layer of strata may be identified and positioned in the sequence according to its fossil content.
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Trilobite Biostratigraphy
Conclusions
Uniformitarianism
Superposition
Original Horizontality
Faunal Succession
These and other principles guide the continual inquiry of geologists worldwide.