OC/GEO103 Lecture 5 Earth Structure
Jan 11, 2016
OC/GEO103Lecture 5Earth 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
Cryosphere
Atmosphere
Hydrosphere
Cryosphere
Biosphere
Atmosphere
Lithosphere
Hydrosphere
Cryosphere
Biosphere
Atmosphere
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
Mid
-Oce
an
Rid
ge
Topography of the Ocean Floor
Mid
-Oce
an
Rid
geDeep-sea
Trench
Topography of the Ocean Floor
Mid
-Oce
an
Rid
geDeep-sea
Trench
Topography of the Ocean Floor
IslandChain
Continents vs Oceans
Elevated Continents
Elevated Continents
Submerged Ocean Basins
•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)
How Big is the Earth?
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
• “Tarzan”• “John Carter of Mars”
Edgar Rice Burroughs
Earth’s Interior is:•Too hot! -- melted rock (magma) comes from even shallow depthsHeat 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 theEarth
• Samples 200km down(e.g., diamonds!)
Seismic Waves
• Sound energyfrom earthquakesand large explosions is recorded at seismometers distributed around the globe
Meteor Crater (Arizona)
Willamette Meteorite
• Found 1902,in West Linn
• Largest inthe U.S.A.
• Sold and nowresides 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.
• 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
Interior of Earth by STRENGTH
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
Mid
-Atla
ntic
R
idge
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.
• 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
PLATE TECTONICS: