Exploring the Deep

GEO/OC103

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

Cryosphere

Atmosphere

Hydrosphere

Cryosphere

Biosphere

Atmosphere

Lithosphere

Hydrosphere

Cryosphere

Biosphere

Atmosphere

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

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

Elevated Continents

Elevated Continents

Depressed 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?

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 theCenter of the Earth”

• Entered in Iceland• Exited in Italy

• “Tarzan”• “John Carter of Mars”

Edgar Rice Burroughs

Information about the Earth’s Interior comes

from:•Meteorites•Volcanoes•Seismic Waves

Meteor Crater (Arizona)

Willamette Meteorite

• Found 1902,in West Linn

• Largest inthe U.S.A.

• Sold and nowresides atthe AMNH

Volcanoes

• E.g., Hawaiian “hotspot”• Windows into the

Earth• Samples 200km down

Seismic Waves

• Sound energyfrom earthquakesand 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.

• 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

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

Mid

-Atla

ntic

R

idge

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.

• 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:

Cracked Egg Shell!