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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.