Earth Structure &

Plate Tectonics

Outline for Today

- Ocean Exploration Recap- National Geographic is a great source

- Everyone participated but written

assignments varied

- Earth Structure- Density is key!!!

- Plate Tectonics- Description of the theory

- Lines of evidence

Learning Goals: History

• The ocean has not prevented human exploration

of the world.

• Many societies have used the ocean for:

• Economic purposes (trading)

• Food

• Cultural connections

• Military power

• Science!

• Navigation and boat-building skills have given

advantages to some cultures.

Eratosthenes (276–194 BC) -

first to accurately determine

Earth’s circumference

Philosopher, mathematician, etc.

Coined the term “geography” – 3 volumes’

book

First one to use latitude and longitude lines

Calculated length of the circumference of

the Earth – fairly accurate for the time

(using shadows from one city and another

on the date of the Summer Solstice)

Admiral Zheng He

Chinese/Muslim during Ming Dynasty – goals

were to explore and flex Chinese muscles

62 treasure ships the size of building 2; 27,800

sailors

To NE Africa and around China– 1 century before

Columbus reached America

7 big voyages; legendary for having one of the

biggest fleets in history. Boats of Columbus and

many other well-known explorers were much

smaller.

Sailed around Vietnam and other islands … to

Indian Ocean 100 years before Portugal did.

Brought back a giraffe from Africa saying it was a

dragon

“The treasure ship, largest in a

vast Chinese fleet whose purpose

was to show kindness to people of

distant places.”

Bob Ballard

- Former US Navy officer and Professor at University of Rhode Island

- Grew up in San Diego

- Worked for Andreas Rechnitzer (deep-sea exploration pioneer)

- When he was at Woods Hole Oceanographic Institution, he persuaded

use of Alvin for underwater exploration

- PhD from URI

- Discovered the Titanic and other things

- See Box 3.1 in your textbook: page 81

Polynesian Voyaging Society

• Established 1973

• No compass – use stars, currents, animal behavior

• Based in Honolulu, HI to perpetuate traditional methods

• Hōkūleʻa to test Polynesian method of navigation

HMS Challenger- 1858: 1st expedition for marine research 68,000 nautical miles

- Physical conditions of deep sea and life forms

- Atlantic, Pacific, Mediterranean, Indian

- Second expedition found the Challenger Trench: 1951

- Investigate life below 1800 feet – found it’s not impossible to have life where

there’s no sunlight

- 4,717 new species discovered

- NASA named a space expedition after the Challenger

TO DATE:

Longest

continuous

oceanographic

expedition:

1872-1876

James CameronFilmmaker, environmentalist, deep sea

explorer – actually the third person to visit

the Mariana Trench (solo dive – over

10,000 meters in depth, in western Pacific

Ocean, to east of Marianas Islands) –

event captured through 3D lens that he

developed. Used Deep-Sea Challenger.

http://geology.com/records/bathyscaphe-trieste.shtml

The Trieste, a bathyscaphe, was the

first vessel to visit the Mariana Trench

(only stayed there for 20 minutes!)

http://education.nationalgeographic.org/encyclopedia/bathyscaphe/

Charles Darwin

Developed the theory of coral reef formation

– 3 types (atoll, etc) before seeing the types.

Galapagos Islands:

theory of natural selection.

Darwin, C. R. 1842. The structure and distribution of coral reefs.

Being the first part of the geology of the voyage of the Beagle, under

the command of Capt. Fitzroy, R.N. during the years 1832 to 1836.

London: Smith Elder and Co.

See animation at:

http://oceanservice.noaa.gov/education/kits/corals/media/supp_coral04a.html

Jacques Cousteau

Jacques Cousteau – explorer, photographer,

filmmaker, military leader, scientist, etc –

mission to safeguard ocean.

With Emile G, created aqualung (J.C. was 35

years old). First test of aqualung by J.C.

Emile Gagnan, co-inventor of the aqualung

Captain James Cook

English explorer – 1728-1779. Considered by

some to be the first marine scientist*. He started

his work in the Royal Navy.

3 voyages. 1st had a secret mission to seek out

Southern Continent (Venus crossing the sun). He

mapped his expeditions.

3rd – within 50 miles of Northwest Passage

* Cook conducted marine

science in the Western

tradition. There were certainly

many earlier scientists (such

as the ancient Polynesians)

who used traditional

knowledge to understand how

nature worked.

Matthew MauryAmerican astronomer, historian, oceanographer,

meteorologist, cartographer, author……

Born on Jan 14, 1806; died in 1873

Navy Commander

Charted wind and ocean currents,

which helped ships to pass each other safely at sea

Nicknamed pathfinder of the seas, father of modern oceanography

Method of recording data was adopted by Navy & Marines (wars).

Could not go to sea any more

at the age of 33 because he

injured his leg in a stagecoach

accident. Instead, he studied

navigation and created charts

from land.

Sometimes people

mistakenly believe that

Maury charted the Gulf

Stream. In fact,

Benjamin Franklin

charted the Gulf Stream

in 1769.

Learning Goals:

Earth Structure & Plate Tectonics• Earth’s layers are arranged by density.

• Land exists because continents float (why?).

• The Earth’s surface is fragile and is broken into

“plates” that are like tiles on a floor. Plates move

as the layer below them moves.

• The collision of plates causes formation of

continents and oceans.

(We’ll talk about this on 1/25)

• Several lines of evidence support the theory of

plate tectonics.

Earth’s layers are arranged by density.

Lighter

matter and

silicates

Iron

Density stratification –

As Earth cooled and solidified, denser materials sank to center,

less dense material remained at surface.

Remember: Density influenced the Earth’s formation.

Temperature increases

as you go deeper

Inner Core –

Solid Iron & Nickel

Why is it solid??

PRESSURE

Outer Core –

Liquid Iron & Nickel

Mantle –

Silicon & Oxygen

Crust -

Solid basalt or granite.

Oxygen, Silicon, Aluminum

Density

• Symbol is ρ

• Mass / volume

• Common units (g/cm3 or kg/m3)

• Density of pure water =

1000 kg/m3 or 1 g/cm3

• Density differences predict fluid motion

Why is density important in

this example?

Another learning goal:

Understand and communicate the main points of a table or

figure of scientific data.

Convection – heat transfer by movement of fluids

The Earth’s Plates:

Definition and Movement

Learning Goals:

Earth Structure & Plate Tectonics• Earth’s layers are arranged by density.

• Land exists because continents float (why?).

• The Earth’s surface is fragile and is broken into

“plates” that are like tiles on a floor. Plates move

as the layer below them moves.

• The collision of plates causes formation of

continents and oceans.

• Several lines of evidence support the theory of

plate tectonics

The Earth’s Plates:

Evidence for Plate Tectonics

What have you already learned about

plate tectonics?

Plate Tectonics

• Alfred Wegener

first proposed in

1912

• Called it

“Continental Drift”

Origin of Continents and Oceans: published in 1915

He noticed South America and Africa fit together.

Evidence for Continental Drift

• Wegener proposed

Pangaea – one large

continent existed

200 million years ago

• Panthalassa – one

large ocean

– Included the Tethys

Sea

• Noted puzzle-like fit of

modern continents

Evidence for Continental Drift

• Matching sequences

of rocks and mountain

chains

• Similar rock types,

ages, and structures

on different continents

Evidence for Continental Drift• Glacial ages and other

climate evidence

• Evidence of glaciation

in now tropical regions

• Direction of glacial flow

and rock scouring

• Plant and animal fossils

indicate different

climate than today.

Evidence for Continental Drift• Distribution of

organisms

• Same fossils found on

continents that today

are widely separated

• Modern organisms

with similar ancestries

The Continental Drift theory was not “perfect” – Wegener was wrong when

he suggested that continents “plow through” ocean basins

Scientific Method

Theory

Hypothesis

“Scientists like to be shown why an idea is correct, rather than being told.”

Evidence for Plate Tectonics

• New evidence from World War II

• Sea floor studies with sonar

• New technology enabled study of Earth’s

magnetic field

Evidence for Plate Tectonics

• Earth’s magnetic field

and paleomagnetism

• Earth has magnetic

polarity

• North and South

polarities

• Magnetic polarity

recorded in igneous

rocks

– Magnetite in basalt

Evidence for Plate Tectonics

• Apparent polar wandering

• Location of North Pole changed over time

Magnetic Polarity Reversals

• Earth’s magnetic

polarity reverses

periodically

• Recorded in ancient

igneous rocks

• 176 reversals in past

76 million years

• Unpredictable pattern

Paleomagnetism and the

Ocean Floor

• 1955 – deep water rock mapping

• Magnetic anomalies – regular pattern of

north-south magnetism “stripes”

• Stripes were symmetrical about long

underwater mountain range

Sea Floor Spreading Evidence

• Frederick Vine and

Drummond Matthews

(1963)

• Analysis of igneous

rock stripes around

mid-ocean ridge

• Sea floor stripes

record Earth’s

magnetic polarity

Plate Tectonic Processes

What does this figure show?

Earthquakes as Evidence

• Most large earthquakes occur at subduction zones.

• Earthquake activity mirrors tectonic plate boundaries.

Global Plate Boundaries

Predicted World Map

50 Million Years in the Future

Types of Plate Boundaries

Divergent

Convergent

Transform

For our next class, 1/25:

1) Choose one type of plate boundary

that you find most interesting (or

confusing):

a) Divergent

b) Convergent

c) Transform

2) Write down the name of one

example of the plate boundary you

have chosen.

3) (Optional) Bring an image (printed or

electronic) of your example.

Recommended source:

http://mapmaker.education.nationalgeographic.com/