Geology
of the NW
Week
one Lecture
On
Line Geologic Dictionary
http://www.glossarist.com/glossaries/science/earth-sciences/geology.asp
Or
use google and search for geologic dictionary
On
Reserve in Library: General Geology
Text. Earth, 8th ed,
Tarbuck & Lutgens
Basic
Geological Principles
Uniformitarianism
James Hutton: Father of geology (1800’s)
No evidence for a beginning of
the earth
No evidence for the end of the
earth
Published Theory of The Earth
Formulated the principle of Uniformintarianism
The physical, chemical
and biological laws that operate today have operated in the geologic past
The
present is the key to the past
What
does uniformitarianism require?
Prior to Hutton, this idea wasn’t articulated.
Age of earth wasn’t known
Many people tried to calculate but
no real way of determining
Geologic time table was organized
but no dates established
Uniformitarianism required earth to be
very old
Actual age of earth established in early
1900’s
Geologic
Time
Considered “deep time”
Earth is measured at 4.6 billion
years in age
Using scientific methods of
measuring radioactive decay rates
Earth’s history is divided into Eons,
Eras, Periods, and Epochs based on the fossil record (extinction events)
Relative
vs. Absolute Dating Techniques
Relative Dating Techniques
Stratigraphic
superposition
Oldest rocks are located on
the bottom of a stratigraphic column.
Original Horizontality
Due to gravity, rocks formed
at the earth’s surface are laid down flat and then
folded
at a later time
Cross cutting relationships
Faunal Succession
Fossils evolve in a logical
and determinable order. Any time period can be recognized based on the fossil assemblege
Unconformities
Erosional
surface captured in the stratigraphy (missing time)
Geo
time table and dating techniques
The geo time table was created using
relative dating techniques.
The actual dates were established using
absolute dating techniques (radiometric dating) in the 1900’s
Earth’s
interior
Comprised of several layers
Core
Inner core
Solid material
Iron/Nickel Composite
Outer core
Liquid material
Iron/Nickel composite
Mantle
82% of the volume of the Earth
Iron Magnesium rock (peridotite).
Two primary regions
Mesosphere (Solid
material)
Asthenosphere (Plastic
material)
Crust (lithosphere)
Two types of crust:
Continental (3.8 b.y. old)à silica rich rocks
30-70 km thick~
2.5 gm/cm3
Oceanic (<180 m.y. old)à iron/magnesium rich rocks (Basalt)
5-15 km thickà
~ 3 gm/cm3
Why
should we care about the interior structure of the earth?
Important because helps to understand the theory of plate
tectonics.
Plate
tectonics
Unifying theory of Geology
Relatively new idea (1960’s)
Started as continental drift in 1915
1960’s
Ocean exploration begins
Found large volcanic mountain ranges in
the middle of the oceans
Magnetic anomaly patterns
Age of oceanic crust followed a pattern
Noticed a pattern to earthquake locations
Develop
theory of Plate Tectonics
Earth’s surface is broken into a series of
plates
These plates move around on the surface
and interact with each other in various ways depending on the type of crust.
Collide
Slide by
Move away
Movement of plates occurs due to the
plastic nature of the asthenosphere and the heat generated inside the earth
Divergent
Plate Boundary
2 plates moving away from each other
Occurs primarily in the ocean crust
Creates the Mid-ocean Ridge system
Largest mountain range on the
surface of the earth
Volcanic ridge
Seamounts form here
Transform
Boundaries
Plates slide by each other
Associated with divergent boundaries
Off set divergent boundaries
Convergent
boundary
Plates come together
3 different outcomes depending on type of
crust involved
Continental to Oceanic Convergence
Continental crust is lighter
and thicker so therefore forces oceanic crust underneath
Subduction zone is formed
Volcanic mountain chain forms
on the over riding plate (continental volcanic arc)
Accretionary
wedge forms
Oceanic to Oceanic convergence
Older crust is more dense so it is subducted under younger crust
Volcanic chain forms on over
riding crust (island arc)
Continental to Continental
convergence
Neither plate subducts….VERY
large mountains are created
Mechanisms
of plate tectonics
Slab pull
Heat convection cells
Radioactive decay
Ridge push
How
do we know the rate and direction of plate motion?
Hot spots/ Mantle Plumes
GPS and Seismometers
Satellite measurements
Volcanic activity
Rock
types
Igneous:
Formed from magma
Intrusive: magma cooled below the surface
Extrusive: magma cooled on the surface
Sedimentary: Forms from compressed, eroded sediments
Metamorphic: Forms when heat and/or pressure is applied to
a pre-existing rock causing the minerals in the rock to change
Earth’s
crust is made up of rocks
Rocks are made up of minerals
Minerals are made up of atoms of
elements
Rock
Cycle