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OC/GEO103
Lecture 5
Earth Structure
What’s inside the Earth?
Is there really another world
at the center?
What is the
energy for changing
surface features?
The Earth System
Atmosphere
Hydrosphere
Atmosphere
Hydrosphere
Atmosphere
Cryosphere
Biosphere
Hydrosphere
Atmosphere
Cryosphere
Lithosphere
Biosphere
Hydrosphere
Atmosphere
Cryosphere
Our Dynamic Earth
• Earth’s surface is constantly
changing
• How do we know it’s dynamic??
•
Earthquakes (and tsunamis)
•
Volcanic eruptions
•
Magnetic Field
•
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
Continents vs Oceans
Elevated
Continents
Elevated
Continents
Submerged
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)
Major Questions:
How are the ocean basins formed?
How permanent are these features?
What is the age of the ocean floor?
What’s the age of the continents?
Why are the ocean basins deep and
the continents high?
The Surface of the Earth
• 2 levels:
– elevated continents
– submerged ocean basins
• What causes these surface features?
• We must know what goes on inside
the Earth
What’s going on inside the
Earth?
Early Ideas
• Jules Verne
“Journey to
the Center of
the Earth”
• Entered in Iceland
• Exited in Italy
Edgar Rice
Burroughs
• “Tarzan”
• “John Carter of Mars”
Earth’s Interior is:
• Too hot! -- melted rock (magma) comes
from even shallow depths
Heat comes from radioactivity
(principally K, U and Th in the mantle)
• Crushingly high pressure! -- no open
spaces!
Information about the Earth’s
Interior comes from:
• Volcanoes
• Seismic Waves (“sound images”)
• Meteorites
Volcanoes
• Hawaiian “hotspot” etc
• Windows into the
Earth
• Samples 200km down
(e.g., diamonds!)
Seismic Waves
• Sound energy
from
earthquakes
and large
explosions is
recorded at
seismometers
distributed
around the globe
Meteor Crater (Arizona)
Willamette Meteorite
• Found 1902,
in West Linn
• Largest in
the U.S.A.
• Sold and now
resides at
the American
Museum of
Natural
History, in
NYC
Dimensions and Boundaries
• 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.
Where does this picture
come from?
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
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
Submerged
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.
– Composed of highly evolved rocks,
like granite, and metamorphic rocks,
squeezed and heated under mountain
ranges
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.
– Composed of basalt (volcanic).
Elevated
Continents
Submerged
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
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