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 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-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

Continents vs Oceans

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 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: 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 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

Thin Oceanic Crust Floats Lower

Mid-Atlantic Ridge

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 :