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/