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-Ocean Ridge Topography of the Ocean Floor

Mid-Ocean Ridge Deep-sea Trench Topography of the Ocean Floor

Mid-Ocean Ridge Deep-sea Trench Topography of the Ocean Floor Island Chain

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 the Center 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 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: gm/cm 3 –Mantle: gm/cm 3 –Core: 10.8 gm/cm 3 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

Thin Oceanic Crust Floats Lower

Mid-Atlantic Ridge

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!