Download Oceanic Crust

GEO/OC103
Exploring the Deep
Lecture 4:
The Structure
of the EARTH
The Edge of the Sea
• "Now I hear the sea sounds about me;
• the night high tide is rising, swirling with a confused
rush of waters against the rocks below ….
• Once this rocky coast beneath me was a plain of sand;
• then the sea rose and found a new shore line.
• And again in some shadowy future the surf will have
ground these rocks to sand and will have returned the
coast to its earlier state.
• And so in my mind's eye these coastal forms merge and
blend in a shifting, kaleidoscopic pattern in which there
is no finality, no ultimate and fixed reality - Earth
becoming fluid as the sea itself."
• Rachel Carson, The Edge of the Sea,  1955
Atmosphere
Hydrosphere
Atmosphere
Hydrosphere
Atmosphere
Cryosphere
Biosphere
Hydrosphere
Atmosphere
Cryosphere
Lithosphere
Biosphere
Hydrosphere
Atmosphere
Cryosphere
Our Dynamic Earth
• Earth is incredibly dynamic
• How do we know it’s dynamic??
•
Earthquakes
•
Volcanic eruptions
•
Surface Features:
– Mountain Ranges; Mid-Ocean
Ridges; Deep-Sea Trenches
Topography of the Ocean Floor
Topography of the Ocean Floor
Topography of the Ocean Floor
Topography of the Ocean Floor
Elevated
Continents
Elevated
Continents
Depressed
Ocean Basins
How Big is the Earth?
• Circumference  40,000 km
(25,000 miles)
• Radius  6,300 km (4,000
miles)
• (1 meter = 1/10,000,000
distance from equator to pole)
Questions:
How are the ocean basins formed?
How permanent are these features?
What is the age of the ocean floor?
Why are the ocean basins deep and
the continents high?
The Surface of the Earth
2 levels:
– elevated continents
– depressed ocean basins
What causes these surface features
We must know what goes on inside
the Earth
Interior of the Earth?
• Jules Verne
“Journey to the
Center of the Earth”
• Entered in Iceland
• Exited in Italy
Edgar Rice
Burroughs
• “Tarzan”
• “John Carter of Mars”
Information about the Earth’s
Interior comes from:
• Meteorites
• Volcanoes
• Seismic Waves
Meteor Crater (Arizona)
Willamette Meteorite
• Found 1902,
in West Linn
• Largest in
the U.S.A.
• Sold and now
resides at
the AMNH
Volcanoes
• E.g., Hawaiian “hotspot”
• Windows into the
Earth
• Samples 200km down
Seismic Waves
Sound energy
from earthquakes
and large
explosions
DEPTHS
• Top of Mantle
– 10 to 70 km (5 to 30
miles)
• Top of Core
– 2,900 km (2000 miles)
• Center of Earth
– 6,300 km (4,000 miles)
• Mt. Everest  9 km high.
• Mariana Trench  11 km
deep.
How do we know what’s inside
the Earth?
How do we know what’s inside
the Earth?
Direct Observations:
• Exposures on Surface
• Up from  50 km (30 miles)
depth
• Drilling
• To  15 km (10 miles)
• Volcanic Material
• Up from  200 km (120
miles) depth
How do we know what’s inside
the Earth?
How do we know what’s inside
the Earth?
Indirect Observations:
• Magnetic Field
• Iron core.
• Gravity Field
• Densities:
– Crust: 2 - 3 gm/cm3
– Mantle: 3.3 - 5.8 gm/cm3
– Core: 10.8 gm/cm3
• Earthquake Seismic
Waves
• Physical state of crust,
mantle, core.
Interior of Earth by STRENGTH
• LITHOSPHERE
–
–
–
–
rigid outer shell
crust and upper mantle (~ 50 to 200 km thick)
somewhat brittle, breakable
cold (like butter out of fridge)
• ASTHENOSPHERE
–
–
–
–
warmer, plastic layer under lithosphere
mantle from ~ 150 to 700 km
squishy, plastic
warm (like softened butter)
• LOWER MANTLE
– Solid, but can flow over time!
– ~700 to 2900 km
• OUTER CORE
– liquid
• INNER CORE
– solid
Elevated
Continents
Depressed
Ocean
Basins
Swimming Pool
Earth’s Mantle
Continental
Crust
Earth’s Mantle
Types of Crust
• Continental Crust
Types of Crust
• Continental Crust
– 20 to 70 km (10 to 30 miles) thick.
Continental
Crust
Earth’s Mantle
Oceanic Crust
Types of Crust
• Continental Crust
– 20 to 70 km (10 to 30 miles) thick.
• Oceanic Crust
Types of Crust
• Continental Crust
– 20 to 70 km (10 to 30 miles) thick.
• Oceanic Crust
– 7 km (4 miles) thick.
Elevated
Continents
Depressed
Ocean Basins
Thick, Buoyant
Continental Crust
Thin, Less-Buoyant
Oceanic Crust
Thick Continental Crust Floats Higher
Thick Continental Crust Floats Higher
Thin Oceanic Crust Floats Lower
Thick Continental Crust Floats Higher
Thin Oceanic Crust Floats Lower
Water Fills in
the Low Areas
And Hides
Features on the
Ocean Floor!
Water Fills in
the Low Areas
PLATE BOUNDARIES
PLATE TECTONICS
• Tectonics:
• From the Greek “tecton”
• builder
•
“architect”
• The study of large features on
Earth’s surface and the
processes that formed them.
PLATE TECTONICS:
• Large features:
– continents, mountain ranges
– ocean basins
• and processes:
– earthquakes
– volcanic eruptions
• due to movement of plates of
Earth’s outer shell.
All resulting from mantle convection
Cracked Egg Shell!