Earth System History

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Chapter 1

• Earth System History

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Earth System History
Study of the inter- connected 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 Earths 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 Earths inner
  regions, and how does it move and deform?

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Earth Systems History

• Earth is an Archive
• Geologic record archives Earths 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
• Application of modern processes to ancient system
• Popularized by 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, 900 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 earths surface
• Intrusive igneous rocks
• harden within the earth

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Sedimentary Rocks

• Sediments
• Material deposited on Earths surface by water,
  ice, or air
• Weathering
• Collective term for chemical and physical
  processes that break down rocks at Earths
  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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Stenos 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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AngularUnconformity
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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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Earths 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
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3
5
4
6
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• Directional Changes in Earths 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