Two conflicting hypotheses
-one based on belief, the
other based on scientific principles.
Catastrophism
- holds that the earth's surface was
created by large-scale cataclysmic events and places
the Earth's age and the complexity of its rocks into a
shortened time span.
Uniformitariansim
- holds that the development of
the Earth's surface is gradual.
� Advanced during the 19th century
� Dictum: "The present is the key to the past.
Earth's Internal Structure
- Core
- Mantle
- Crust
Core
- Inner Core
- Outer Core
Mantle
- Lower
- Upper (Asthenosphere, rigid zone)
Crust
- Oceanic
- Continental
Earth's Core
Inner Core
� Solid iron and extremely hot.
� High pressure keeps it solid.
Outer Core
� Molten metallic iron.
� Will not transmit secondary earthquake
energy waves.
� Generates the Earth's magnetic field
Description of Mantle
� 80% of the Earth's total volume
� Lower Mantle
� Upper Mantle
� Asthenosphere - Plastic layer containing pockets of heat and slow
convective currents
� Rigid zone (part of Lithosphere). Upper boundary is the Moho
Discontinuity
Oceanic Crust
Dark basaltic rock,
� Relatively thin
� Relatively young
� Very dense
Continental Crust
Light granitic rock
� Thick
� Relatively old
� Lower density
Continental Drift
Proposed by Alfred Wegener in 1912.
� Argued that 225 million years ago present landmasses were part of a
supercontinent which he called Pangaea.
� This latter rifted into Laurasia and Gondwanaland
� Offered lots of evidence but could not explain the mech
Sea Floor SPreading
Proposed by Harry Hess and Robert Dietz in
the early 1960s.
� Sea-flooring expanding along mid-oceanic ridges.
� Drive continents apart in some areas and together in others
� Sea-floor was being destroyed in other areas
� Subduction of ocean floor into th
Evidence of Plate Movements
Continental landmasses approximately fit together
� Fossil evidence abounds
� Magnetic reversals (paleo-magnetism)
� Rocks of the ocean crust increase in age with
distance from mid-oceanic ridges
� Able to measure movement of land masses.
� The plates and
Divergent Boundaries
Where new sea-floor is created and plates move apart.
Convergent Boundaries
Where plates collide
Oceanic crust to Continental crust
more dense oceanic crust is subducted (thrust
downward) into the mantle.
� Continental crust is thrust up.
Oceanic crust to Oceanic crust
Subduction - Island arc formations
Continental Crust to Continental Crust
crush zone
� Mountain building
Transform
Where plates slide past one another
Hot Spots
� Individual sites of upwelling materials
from the mantle.
� Deeply anchored in the mantle and remain
fixed beneath migrating lithospheric
plates.
Summary
Ideas regarding the development of the Earth's surface have changed
dramatically over the past 200 years
� The Earth's interior consists of an inner core and outer core, mantle, and
crust
� The lithosphere consists of the upper mantle and the Earth's crus