Earth : Plate Tectonics and Magnetic Field

Lecture 17

OASIS in the Solar System

Dynamic Earth

Energy Sources of Dynamic Earth

Solar energy, tidal forces, and internal heat (trapped heat + radio active material)

Formation & evolution of Earth

Differentiation

How do we know the internal structure of the Earth?

Based on the propagation pattern of seismic waves, scientists deduced that there should be 3 layers inside of the Earth!

Internal Structure of Earth

Internal Energy Source convection

Plate Tectonicshttp://www.youtube.com/watch?v=ZLJLFYXp-0Q

Continental Drift

Continental Drift was proposed by meteorologist and geologist Alfred Wegener in 1912

The idea was inspired by the puzzle-like fit of South America and Africa, indicating these two continents were part of a single “supercontinent” about 200 million years ago

Fitting the Continents Together Africa, Europe, Greenland, North America, and

South America fit together remarkably well.

Plate Tectonics

Internal heat makes hot material expand and rise while cooler material on top contracts and falls

Plate tectonics produces and recycles seafloor crust (that is why the seafloor crust is usually less than 200 million years old). At ocean trenches, the seafloor crust pushes under the less dense continental crust, returning the seafloor crust to the mantle and may cause volcanic eruptions.

8 major plates + dozens of smaller platesMajor Earthquakes happened at plate boundaries

Boundaries of Plates

At plate boundaries…

Hot SpotsSometimes, localized plume of mantle material get uplifted…

Hawaiian islandsYellow Stone Park

On-going…

In ~100 Myrs, California will slide northward to Alaska, the Mediterranean Sea will become mountains, Australia will merge with Antarctica

Plate Tectonics CO2 Cycle

On Earth, CO2 content in the air is regulated by the Carbon Dioxide Cycle to avoid runaway Greenhouse effect

Carbonate rocks : limestone, calcite, dolomite, chalk, …

Plate tectonics is the key element of long-term stability of the Earth!

CO2 in the Earth : atmosphere 1, ocean 60, rocks 170,000

Cause of Magnetic Field

Electromagnet

Requirements for a magnetic field• Electrically conducting fluid• Convection• Rotation of the planet

Magnetic field interacts with Solar winds!High velocity electrified gas (plasma) blows into the Earth at speed of ~250 miles/second!http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/20020509imagessu/magneticfield_mpeg.mpg

Magnetic Field

Charged particles from solar flares interact with earth’s magnetic field and atoms and molecules in Earth’s atmosphere and produce aurora.Without the magnetic field, our atmosphere would have been stripped away by the strong solar wind!

Aurora Borealis : Aurora Australis :

Auroras : northern & southern lights

Aurora in Georgia!Oct. 29, 2003. Dahlonega, GA

Triggered by a coronal mass ejection…

On other Planets, too!

Jupiter seen in X-ray (Chandra satellite)Saturn seen by Cassini (optical)

In summary…

Important ConceptsEnergy sources of EarthInternal structure of EarthPlate Tectonics• plate boundaries

Magnetic field • cause• as a shield

Important TermsAsthenosphereConvectionPlate tectonicsDifferentiation

Chapter/sections covered in this lecture : sections 9-1 through 9-4