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Chapter 1
Earth System History
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Earth System History
Study of the interconnected physicochemical
and biological changes that
our planet has experienced
over the course of geologic
time
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Guiding Questions
• What fundamental principles guide geologists as
they reconstruct Earth’s history?
• What are the basic kinds of rock and how are they
interrelated?
• How do geologists unravel the age relations of
rocks?
• How does the lithosphere relate to Earth’s inner
regions, and how does it move and deform?
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Earth Systems History
Earth is an Archive
– Geologic record archives Earth’s
history
– Interaction of complex systems within
the planet
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Foundations of Geology
• Principle of
Uniformitarianism
– There are inviolable
laws of nature that
have not changed in
the course of time
– First founding
principle of geology
• Actualism
James Hutton
– Application of modern
processes to ancient
system
– Popularized by
Charles Lyell
Charles Lyell
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Actualism
Modern ripples
provide clues to
ancient systems.
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Catastrophism
• Earth forms (mountains, Grand
Canyon, rock layers, fossils found
high in the mountains) were due
to catastrophic forces that shaped
the world in a relatively short
time.
• Leads to ‘Young Earth’ concept
• Bishop James Ussher of Ireland
– October 26, 4004 BC, 9:00 am
– ~6000 years
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Materials and Processes
• Rock
– Interlocking or bonded grains of matter typically
composed of single minerals
• Mineral
– Naturally occurring inorganic solid element or
compound with a particular chemical composition or
range of compositions and a characteristic internal
structure
• Outcrop
– Rocky surfaces that stand exposed and are readily
accessible for study
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Rock Cycle
• Surface and internal
processes link
materials to form three
rock types:
– Igneous
– Sedimentary
– Metamorphic
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Igneous Rocks
• Formed by cooling of molten material to the
point of hardening
– Composed of bonded grains, each consisting of
a particular mineral
• Magma
– Molten material that turns into igneous rock
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Igneous Rocks
• Extrusive igneous
rocks
– harden at the earth’s
surface
• Intrusive igneous
rocks
– harden within the earth
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Sedimentary Rocks
• Sediments
– Material deposited on Earth’s surface by water,
ice, or air
– Weathering
• Collective term for chemical and physical processes
that break down rocks at Earth’s surface
– Erosion
• Processes that loosen pieces of rock and move them
downhill
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Sedimentary Rocks
• Formed from:
– Preexisting rocks (clastic rocks)
• Sandstone
• Shale
– Skeletal debris
• Limestone
– Chemical precipitates
• Evaporates
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Sedimentary Rocks
• Stratum:
– Tabular layer
of sediment
accumulated
in discrete
episodes
– Bed
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Metamorphic Rocks
• Formed by alteration of preexisting rocks
under high temperatures and pressure
• Alteration occurs without melting rocks
– Density increases
– Crystals enlarge
– Lineation of some minerals
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Rock Units
• Formations
– Unit of rock formed in a particular way
– Formally named, often for nearby geographic feature
• Catskill Formation
• Member
– Smaller rock unit
• Group
– Groups of formations
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Steno’s Principles
• Principle of Superposition
– Oldest strata are at the bottom in an
undisturbed sequence of strata
• Principle of Original
Horizontality
– All strata are horizontal when they
form
• Principle of Original Lateral
Continuity
– Strata originally are unbroken flat
expanses
– Interrupted by erosion
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Cross-cutting Relationships
• Principle of Intrusive
Relationships
– Intrusive igneous rocks are
always younger than the
rock they invade
• Principle of Components
– Fragments within a second
body of rock are older than
the second body of rock
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Fossils
• Remnants of ancient
life, thousands to
millions of years old
• Fossil succession
– Date by comparing
them to fossils
throughout the world
– William Smith
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Unconformity
• Substantial interval of
time when erosion
occurred rather than
deposition
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Unconformity
– Angular unconformity
– Disconformity
– Nonconformity
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Angular
Unconformity
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Geologic Time Scale
• Developed using
– Biostratigraphy (fossil succession)
– Radioactive decay
• Divided into
– Phanerozoic
– Precambrian/Archean
• Cambrian
– Oldest rocks with conspicuous
fossils
See p. 12
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Earth’s Interior
• Crust
• Mantle
• Core
– Mohorovicic
Discontinuity (Moho)
• Crust/mantle boundary
• Lithosphere
• Asthenosphere
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Plate Tectonics
• Crust
– Oceanic
• Mafic (Mg- and Fe- rich)
– Continental
• Felsic (Si-rich, lower in Mg and Fe)
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Plate Tectonics
• Movement of lithospheric plates
• Plates formed at spreading centers,
destroyed at trenches
• Driven by convection
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Convection
• Material heated deep
in asthenosphere rises
to displace cooler less
dense material nearer
the surface
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Spreading Zones
• Plates move apart
• Mid-ocean ridge
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The land of fire and ice
Mid-Atlantic Ridge, a spreading zone
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Subduction Zones
• Trenches
• Associated
with
volcanoes
– Partial
melting of
lithosphere
Animations
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Hydrological (Water) Cycle
• Water
– Abundant
– High heat capacity
• Water cycle
– Exchange between reservoirs
•
•
•
•
Atmosphere
Biosphere
Hydrosphere
Groundwater
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Evolution
• The process by which particular forms of life give
rise to other forms by way of genetic changes.
• Natural selection
– Primary mechanism of evolution
– Process operates on heritable variability, selection
results from differences among individuals in longevity
and production of offspring
• Extinction
• Mass extinctions
– Global catastrophes in which large percentage of
species disappeared
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The Six Mass Extinctions
1
3
2
5
4
6
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Directional Changes in Earth’s History
•Initial views of Earth
•Internal energy
•Solar energy
•Evolution of life
•Life shapes environment and vis versa (reducing to oxydizing
atmosphere
Episodic changes (External and Internal causes)
•Asteroid impacts
•Milankovitch
•Earthquakes
•Sedimentation
•Extinctions
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