Lecture
notes Weeks 1 & 2
What
is Science and how is it “done?”
The
Scientific Method
Observation
Develop a hypothesis
Test your hypothesis
Accept, reject or modify your hypothesis.
What
is the difference between an hypothesis, a theory and
a law?
Why
study geology?
Geology
is:
An attempt to understand our environment
Recognizing earth processes
Unraveling geologic history
Better appreciate earth’s limits
Discovering natural resources
Environmental protection
ID and protect society from hazards
What
are some of the “specialties” in geology?
What
are the two basic categories or “types” of geology?
Physical Geology
Studying the
functions and mechanics of various processes on earth.
Includes the study of
Rocks and minerals
Earthquakes &
Volcanoes
Environmental geology
Structural geology
Hydrology
Historical Geology
Studying the history of the Earth
and how it has changed over time
Evolution of life on earth
Earth History
Evolution of continents,
oceans, atmosphere etc…
Evolution of the earth and the
solar system
What
tools do geologist use to study the earth?
Rock
types
Igneous:
Formed from magma
Intrusive: magma cooled below the surface
Extrusive: magma cooled on the surface
Sedimentary: Forms from compressed, eroded sediments or
evaporation
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 elements (more on
this later)
Rock
Cycle
Earth
is a system
What is a system?
How can earth be considered a system?
4 spheres in the “Earth system”
Biosphere
Geosphere
Atmosphere
Hydrosphere
History
of geology
Geology is a “young” science
17th & 18th centuries defined by
catastrophism (idea that is earth 6000 yrs old)
The earth’s surface is shaped
by sudden and large catastrophic events
Changes in the earth’s surface
occurred over relatively short time periods (days to weeks)
18th & 19th centuries tried to
define age of earth through scientific evidence.
James
Hutton: Father of geology (1800’s)
No evidence for a beginning of the earth
and no evidence for the end of the earth
Formulated the principle of
Uniformitarianism
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 that catastrophism doesn’t?
Geologic
Time
Considered “deep time” (billions of years)
Earth’s age is measured at 4.6 billion
years.
This age is calculated using the
radioactive decay of elements
The geologic time table breaks down the
history of the earth into eons, eras, periods and epochs
Divisions are based on the
fossil record (extinction events)
Which
philosophy, catastrophism or uniformitarianism, do geologists subscribe to
today?
The
Big Bang vs. Solar Nebular Hypothesis
Earth’s
Structure:
Layered:
Densest material in center (10-13 g/cm3) and least dense on outside (2.8-3 g/cm3)
Each region is compositional distinct
Details:
Core: Iron/Nickel composite
Inner: solid (13g/cm3)
Outer: Liquid (10 g/cm3)
Mantle: Peridotite
(iron/magnesium rich rock)
Mesosphere (lower
mantle): solid (5.7 g/cm3)
Asthenosphere: plastic (3.3 g/cm3)
Upper Mantle: Solid
Lithosphere: solid
Upper most mantle and
Crust
Crust (two
types):
Oceanic:
5-10 km thick, 3g/cm3
iron and magnesium rich (Basalt)
Continental:
20-90 km thick, 2.7g/cm3
silicon rich
Plate
tectonics
Unifying theory of Geology
Relatively new idea (1960’s)
Started as continental drift
Idea introduced in 1915
Plate tectonics re-birthed in 60’s
End
week 1: Homework questions (Due Mon 10/6
or Tue 10/7)
101/201: Read chapter 2 (pg 37-54) and then, in your
own words, explain the theory of plate tectonics and the different type of
plate boundaries (give details). Give a
real world example of each type of plate boundary.
201:
Explain in your own words, why mineral resources form at convergent and
divergent boundaries.
Theory
of Plate Tectonics
Earth’s crust is broken into several
plates
Plates interact with each other in
different ways
Collide
Slide by
Move away
Divergent
Boundaries
Plates move away from each other
Volcanic mountain chain creates new ocean
crust (basalt)
Known as a ridge or rift and has a valley
in the center
Usually located in the middle of the
oceans…exceptions?
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
REVIEW:
Continental Crust vs. Oceanic crust…which is the thickest? Which is the most dense?
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
The
oldest ocean crust is only ~180 million years old.
Why is there no really old oceanic crust?
Driving
Mechanisms for Plate Tectonics
Examine the uppermost region of the
asthenosphere to understand what is happening
Melt zone represents “weak” area and
this zone allows Lithosphere to “detach” from the asthenosphere and move
How did plate motion begin?
Heat generated inside of earth began the
motion of convection
What is convection?
Where does the heat come from to
drive convection inside the earth?
Slab Pull
Due to weight of crust as it is
“pulled” into earth at subduction zones
Ridge push
Gravitational “push” of material
piling up at ridges
How
do Plate boundaries relate to earthquakes and volcanoes
Do Volcanoes always occur on plate
boundaries?
Hot spots/ Mantle Plumes
How
do we know the rate and direction of plate motion?
Use hotspots
Use instrumentation
GPS, Seismographs
etc…
Earth Scope
Project
Intro
to Earthscope
This is a project designed to:
Study how the N. American continent
grew/formed
Study how lithospheric
plates interact with each other
Understand better about how the
continent changes due to earthquakes and volcanic eruptions
It will do this by using
GPS, strain meters and magnetometers (PBO)
Seismometers (permanent and rolling
array)
Satellites