GEOLOGY 117 -- THE OCEANS

Get to web site from Illinois Compass Instructor: Prof. Tom Johnson [email protected]

Web Notes and Readings

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One set of notes for each class; linked to class schedule on web page

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Short reading assignments to be done

before

classes; listed in class schedule on web page

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Get to the web page through Compass

What is Science?

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A collection of facts about nature?

It’s 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?.....

Science is often reliable.

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 don’t hold up – useless.

-Others do withstand the tests of time- useful!

-So we test them- BIG TIME

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.

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.

Subdivisions of ocean science: Marine geology Chemical oceanography Physical oceanography Biological oceanography This is the basic order of topics in this course.

Class #2 -- Geology 117

The Earth, Part 1

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?

Latitude

Latitude lines are “parallels”: constant distance between

Longitude (East-West) Why measure longitude in degrees???

Continents mostly in the N hemisphere: Gives Earth a slight “pear” shape

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

Layering of the Earth Based on Chemical Composition

Layer

Crust - Continental Crust - Oceanic Mantle

Depth (km)

55 (25-90) 10 (5-10) to 2900 Core Outer Core Inner 2900 5300 5300 6370

State Comp.

solid (rigid) solid (rigid) solid (ductile) liquid soild "granite" basalt Mg, Fe silicates Fe, Ni metal Fe, Ni metal

g/cm3

2.7

3.0

4.5

11.5

13.0

TÞC

<1000 <1500 1500 3000 4000 5000

Fig. 1.14

in Text

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

P and S wave material not in textbook

http://www.eas.purdue.edu/~braile/e dumod/waves/Pwave.htm

http://www.eas.purdue.edu/~braile/e dumod/waves/Swave.htm

P- waves (refraction, shadow zone) S- waves (blocked by liquid, large shadow zone Homogeneous earth would be like this:

Homogeneous earth would be like this:

P and S wave material not in textbook http://neic.usgs.gov/neis/eq_depo t/2002/eq_021103/ak_seismic_w aves.html

P- waves (refraction, shadow zone) S- waves (blocked by liquid, large shadow zone Homogeneous earth would be like this:

More evidence used to infer what’s inside the earth...

More evidence used to infer what’s inside the earth...

• Meteorites – Some are fragments of planets; broken apart billions of years ago – Some are Fe Metal – Some are Mg+Fe silicates like the earth’s mantle

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

Represents amount of uranium Represents amount of lead