OC/GEO103 Lecture 5 Earth Structure. What’s inside the Earth? Is there really another world at the...

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: