Lecture 2 -- Geology 117

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GEOLOGY 117 -- THE OCEANS Get to web site from
Illinois Compass Instructor Prof. Tom
Johnson tmjohnsn_at_uiuc.edu
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Web Notes and Readings

• One set of notes for each class linked to class
  schedule on web page
• Short reading assignments to be done before
  classes listed in class schedule on web page
• Get to the web page through Compass

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What is Science?

• A collection of facts about nature?
• -Its much more than that
• A process or method used to decide what is true
  and what is not?
• -It is that, too.
• A collection of ideas dreamed up by scientists
  that keeps changing and is never really
  reliable?.....

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Science is often reliable.
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• How science progresses, succeeds, and fails
• We observe the world around us.
• We try to make sense of it all. If we succeed at
  that, then maybe we can predict what will happen,
  or find a way to make something useful.
• We make educated guesses- Hypotheses.
• Some dont hold up useless.
• Others do withstand the tests of time- useful!
• So we test them- BIG TIME

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• How science progresses, succeeds, and fails
• Sometimes an idea becomes more than just an
  educated guess. After much testing, it really
  seems to work, and we call it a theory. Some
  theories are well established and reliable.

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• How science progresses, succeeds, and fails
• Sometimes an idea becomes more than just an
  educated guess. After much testing, it really
  seems to work, and we call it a theory. Some
  theories are well established and reliable.
• Some theories are revised or overturned
• - This does not mean that science is haphazard-
  it is part of the normal process
• - We will examine the development of the theory
  of plate tectonics in this class. 

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Subdivisions of ocean science Marine
geology Chemical oceanography Physical
oceanography Biological oceanography This is the
basic order of topics in this course.
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Class 2 -- Geology 117

• The Earth, Part 1

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The Oceans- Part 1 Marine Geology

• How did the Earth and Oceans form?
• What does the ocean floor look like (shape)?
• Why is it shaped that way?
• Why does the earth have oceans and continents
  instead of just a single shallow ocean covering
  everything?
• How do we know all this stuff anyway?
• Do we really know or is it more inference
  than knowledge?

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Latitude
Latitude lines are parallels constant
distance between
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Longitude (East-West)
Why measure longitude in degrees???
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Continents mostly in the N hemisphere Gives
Earth a slight pear shape
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When did the earth form and how did it form? How
did it get to be what it is today?

• About 5 B.Y. ago Formation of the solar system
  Gravitational collapse, rotating disk dust
  and gas (mostly H and He)
• Then accretion -- planets.
• Earth, other planets, meteorites at 4600 m.y.
• Early molten(?) stage of Earth (first 200 m.y.)
  
• - silicate mantle and metallic core formed

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Layering of the Earth Based onChemical
Composition
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Fig. 1.14 in Text
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What is the evidence for this?

• The way earthquake waves travel through
• Each earthquake sends out waves
• Thousands of seismographs detect these
• e.g., Earthquake in Turkey, detected here
• Two types of earthquake waves
• compressional waves, or P waves
• shear waves or S waves

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P and S wave material not in textbook
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http//www.eas.purdue.edu/braile/edumod/waves/Pwa
ve.htm http//www.eas.purdue.edu/braile/edumod/w
aves/Swave.htm
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P- waves(refraction, shadow zone)
S- waves(blocked by liquid, large shadow zone
Homogeneous earth would be like this
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Homogeneous earth would be like this
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P and S wave material not in textbookhttp//neic
.usgs.gov/neis/eq_depot/2002/eq_021103/ak_seismic_
waves.html
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P- waves(refraction, shadow zone)
S- waves(blocked by liquid, large shadow zone
Homogeneous earth would be like this
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More evidence used to infer whats inside the
earth...
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More evidence used to infer whats inside the
earth...

• Meteorites
• Some are fragments of planets broken apart
  billions of years ago
• Some are Fe Metal
• Some are MgFe silicates like the earths mantle

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How do we know when all this happened (age
dates)?

• Radioactive elements
• Decay produces daughter products
• Some radioactive elements have very long
  half-lives (e.g., Uranium)
• Buildup of daughter products can be used to
  determine ages of rocks and meteorites

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Represents amount of uranium
Represents amount of lead