A Short History of Historical
Geology I - Steno to Lyell
Earth History prior to the 1600’s
• The chronology of the Judeo-Christian Bible
• J. Ussher, The Annals of the World (1658)
• Creation of the Earth began the nightfall
before Sunday, 23 October, 4004 BC
James Ussher,
Archbishop of Armagh
Earth History prior to the 1600’s
• The Earth was about 6000 years old.
• All of the animals and plants that lived on the
Earth had been present since its creation.
• Fossils - the remains of past life - were not yet
recognized as such.
• Extinction was inconceivable.
Nicholas Steno
(1638-1686)
• Danish anatomist
• Member of the Court of
Grande Duke of Tuscany
• Later in life became a
Catholic bishop and
eventually a Saint.
Tongue Stones - Glossopetrae - Fossil Shark Teeth
Hey, I should
write a book!
The Prodromus!
Problem: how does the shark
tooth get inside of the rock?
De solido intra solidum naturaliter
contento dissertationis prodromus
Nicholas Steno
(1638-1686)
“Preliminary discourse to a dissertation on a
solid body naturally contained within a
solid.”
Steno’s Laws
Steno proposed 3 laws for
understanding how rock layers
form.
Nicholas Steno
(1638-1686)
Original Horizontality
•Rock layers form from the settling of mineral
grains into tabular sheets (beds) that are
horizontal when formed.
Sand settling out of water
Original Horizontality
Original Position of All Layers
•Rock layers that are
tilted were deformed
after being
deposited.
Principle of Superposition
• Given that rock layers form from the settling of
mineral grains...
Deposited last
Deposited first
Principle of Superposition
• Given that rock layers form from the settling of
mineral grains...
• Rock layers get younger “upsection”
Youngest layer
Oldest layer
Principle of Cross-cutting
relationships
•Object embedded in rock must have existed
before the rock because it cuts across the rock.
Principle of Cross-cutting
relationships
•Object embedded in rock must have existed
before the rock because it cuts across the rock.
Tooth exists before rock layer forms.
Principle of Cross-cutting
relationships
•Object embedded in rock must have existed
before the rock because it cuts across the rock.
Tooth forms after rock layer (impossible).
Steno made it possible to begin thinking
about a process of formation for rock
layers:
• Rock layers form by a sequence of events.
• They have a history.
• The history can be reconstructed by
studying the layers.
• The Earth preserves a record of its own
history of formation and traps objects and
information within rock layers.
Early Theories of the Formation
of the Earth - Neptunism
Abraham Werner
(1750-1817)
• Studied minerals and mining
• Professor at the Mining Academy of
Frieberg
• Brilliant and charismatic lecturer
• Postulated that the deep rock of the
Earth’s crust initially crystallized out of a
primordial ocean.
• Younger rock layers formed from the
erosion of the older rock.
• Did not accept that the interior of the
Earth was hot - denied the existence of
volcanoes.
• Trained a generation of geologists.
Neptunism - the theory that the rocks of the Earth
crystallized out of a primordial ocean
Primordial ocean
Earth’s
interior
•Primary - the first rock that formed - crystallized
out of the ocean forming an irregular layer.
Earth’s
interior
•Primordial ocean recedes, exposing primary rock.
•Primary rock begins to erode, material mixes with
crystallizing rock, forming Transitional rock.
Transitional rock
Earth’s
interior
•Primordial ocean continues to recede.
•Primary rock stops forming, continues to erode.
Earth’s
interior
Eroded Primary and Transitional rock is redeposited
in layers of Secondary strata.
secondary
Primary and Transitional
Later erosion produces Tertiary strata.
Tertiary
Secondary
Primary and Transitional
The Noachian Flood produces Diluvial deposits of
sand and gravel.
Diluvial
Tertiary
Secondary
Primary and Transitional
Early Theories of the Formation
of the Earth - Plutonism
James Hutton
(1726-1797)
• Scottish farmer, chemist and geologist.
• Defender of the Plutonist theory of the
Earth.
• Published “Theory of the Earth” in 1795
• Postulated endless cycles of rock
formation, upheaval, and erosion.
• Few could get past his dense, awkward
prose.
• Playfair’s “Illustrations of the Huttonian
Theory of the Earth” finally convinced
most geologists of the validity of his
ideas.
Plutonism - the theory that the Earth’s interior is hot.
•Crystalline rock forms from molten rock
erupted from the Earth’s interior.
•Sediments fuse into rock by heat and pressure.
•Volcanoes release heat from Earth’s interior.
•Interior heat causes periodic upheavals of the
crust of the Earth.
Hutton’s angular unconformity at Siccar Point, Scotland
Hutton’s angular unconformity at Siccar Point, Scotland
Old Red Sandstone
Transitional slates
Deposited first, in horizontal layers
Transitional slates
Uplifted, tilted and eroded.
Transitional slates
Deposition of Old Red Sandstone
Transitional slates
Younger uplift, tilting, and erosion of all layers.
Old Red Sandstone
Transitional slates
Geological Cycles Shown at Siccar Point
“No vestige of a
beginning.
No prospect of an end.”
• Erosion of older rock
• Deposition of Transitional slates
• Uplift and tilting of slates
• Erosion of tilted slates
• Deposition of overlying Old Red Sandstone
• Uplift and tilting of all layers
• Erosion of tilted layers (happening now)
“The present is the
key to the past.”
Charles Lyell
(1797 - 1875)
Uniformitarianism
• Published 3 volume Principles of Geology
- first “textbook” of geology.
• Argued “Uniformitarianism” - the idea that
the geologic events that occurred in the
past were no different from those
occurring today.
• Studying modern geologic events and
processes is a reliable guide to interpreting
the past.
• Provided examples and methods for
interpreting rock layers in the field.
Charles Darwin read and applied Principles of
Geology during his
voyage around the
world on the
H.M.S. Beagle.
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