Earth Science: Plate Tectonics

How do we see inside the Earth? Waves Seismic waves Seismology Study & measurement of seismic waves What do we know that produces seismic waves?

Two main types of waves “P” Waves “S” waves

P-waves “P” or Primary waves Longitudinal Compress and expand Fastest Travel through all mediums ( solid, liquid and air)

“S” Waves “S” or Secondary waves Transverse Vibrate up and down / side to side Slower than “P” waves Only travel through solids

Layers of the Earth

The Crust Surface layer Like an eggshell Thin Brittle Can crack Two regions: Oceanic (Basalt rock) Continental (granite rock) Crust is less dense than the mantle Like ice on water; the crust floats on the mantle

The Mantle

The Mantle Rocky Like the crust Silicon Oxygen Iron, magnesium, calcium are heavier elements Mantle is denser How does the Earth’s crust add to the density of the mantle? Weight bearing down on the mantle…it compresses the minerals, increasing the pressure and squeezing them into rocks.

The Mantle Higher temperature Why? Increased pressure Decay of radioactive elements

Layers of The Mantle Upper mantle Lithosphere Asthenosphere Rigid rock upper portion of upper mantle Asthenosphere Lies beneath lithosphere and “flows” like plastic It is solid…silly putty Lower mantle

The Core Two layers: inner and outer core 15% Earth’s volume 30% Earth’s mass 2x as dense as the Earth’s mantle Why? Made of metallic iron Inner core is VERY hot! Some places as hot as the surface of the sun!

The Inner Core Solid Iron How? Pressure from Earth keeps Iron packed tightly; doesn’t allow it’s atoms to flow

The Outer Core Outer Core Liquid Iron Less pressure Flows and spins as Earth rotates Creates convection currents Affects Earth’s surface Produces electrical charge Possibly responsible for Earth’s magnetic field

Magnetosphere

Convection Currents What are convection currents? Current of heat flows from core to crust This sets up a convection current in the mantle

Effects of Convection Currents When the current comes at a weaker part of the crust, for example at a volcano, magma comes above the earth's surface. This is called plate tectonics. The movement of these plates goes very slowly. The bumping of two tectonic plates causes an earthquake. The convection current along the bottom of the crust causes the moving of the tectonic plates.

Continental Drift & Tectonic Plates Wegner’s Hypothesis on Continental Drift The World’s continents are in motion At one time, the continents were joined together as one… This was known as Pangea They fit together like a jigsaw puzzle

What caused the continents to separate?

Continental Drift Wegner’s theory that proposed the landmass known as Pangea started breaking up Separated into two parts: Laurasia and Gondwanaland Wegner’s theory of the separation of Pangea was supported by fossil, biological, climatological and geological evidence

Seafloor Spreading Seafloor is not permanent Constantly renewing itself Mid Atlantic Ridge (longest & tallest mountain range in the world, center of the Atlantic Ocean) Forms islands: Iceland and Azore There are rifts in the mountains

Plate tectonics Continents move because they are embedded in plates The plates shuffle or move atop of the Earth’s surface Plates move in different directions and different speeds from each other There are nine large plates and several smaller plates

Plate Boundaries Divergent Boundaries Plates move away from each other Comes from rock in athenosphere Partially melted The rock partially melts = lava It was magma before it left the surface of the Earth

Convergent boundaries Plates move toward each other

Transform fault boundaries Plates slide past each other

Earthquakes Devastating Stress (force) applied to rock Stress causes strain Eventually the rock cannot bend anymore It breaks and releases stored energy The released energy ( Seismic Waves) travel out in all directions

Earthquakes cont The initiating site of the seismic wave: focus The point at Earth’s surface directly above the focus: epicenter Measured on a Richter Scale ( the incraments are ten fold in magnitude…

Tsunami Seismic sea wave Created by an earthquake