Chapter 12 Section 3 Earths Interior Basic Layers

Chapter 12 Section 3: Earth’s Interior

Basic Layers of the Earth • Crust • Mantle • Outer Core (liquid) • Inner Core (solid)

Earth’s Crust • Continental Crust: rock layer under continents made of mostly granite • Oceanic Crust: rock layer under oceans made mostly of basalt • Basalt is much more dense than the granite. Less dense continents ride on the denser oceanic plates.

The Lithosphere • The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the lithosphere. • The crust is broken into pieces called plates. The lithosphere makes up Earth’s plates.

The Asthenosphere • The asthenosphere is the part of the middle mantle that flows gently like melted plastic. • Lithosphere or Earth’s plates ride on top of the asthenosphere.

Convection Currents • The middle mantle or asthenosphere moves Earth’s plates due to convection currents. • Convection currents are caused by the very hot material at the deepest part of the mantle rising, cooling & sinking again.

Outer Core • Under the mantle is Earth’s outer core. • The outer core is so hot that the metals in it are all liquid. Outer core is made of the metals nickel and iron.

Inner Core • The inner core of the Earth has temperatures and pressures so great the metals are squeezed together to create a solid.

Earth’s Magnetic Field • Don’t forget: Earth’s magnetic field is caused by the spinning of the molten iron core!

Chapter 12 Section 1

Continental Drift • In 1915, Alfred Wegner hypothesized the continents were once part of a supercontinent called Pangea. Over time, the continents drifted apart.

Proving Wegner Correct • Over time, there were three pieces of evidence found that supported Wegner’s idea: – Matching coastlines: South America looks like it fits with the coast of Africa – Matching fossils: The same fossils from ferns and dinosaurs are found on multiple continents. – Matching rocks and mountain ranges: When continents fit into Pangea, it shows mountains were originally one large mountain range.

Matching Coastlines

Matching Fossils

Matching Mountain Ranges

Sea Floor Spreading • Dr. Harry Hess used sonar to map the seafloor and revived Wegner’s ideas. • Discovered a midocean ridge, or MOR, around the Earth.

MOR • Magma from the mantle is forced up due to its low density (convection currents). • This causes the ocean crust to crack (fault) and move apart. This is sea floor spreading! New oceanic crust is created.

Mid-Ocean Ridge Around the Globe

Mountains and Rift Valleys • The MOR creates a twin mountain range along the fault. • A rift valley is also produced with the mountain range.

Which crust is older?

Theory of Plate Tectonics • Plate tectonics- The theory that pieces of the Earth’s lithosphere are in constant motion, driven by convection currents in the mantle • No plate can move without affecting the other plates surrounding it; they must bump, grind, or pass each other in order to move. • Remember, the plates of the lithosphere float on top of the asthenosphere (the top layer of the mantle)

Divergent Plate Boundary • Divergent Boundary: the spreading apart of two plates. Examples: MOR and in East Africa. • Features: Rift Valley, mountain range for MOR, deep ocean trench, earthquakes

Transform Plate Boundary • Transform Boundary: two plates that move past each other horizontally • Examples: western US called the San Andreas Fault • Features: Earthquakes

Convergent Plate Boundaries • Convergent Boundary: two plates that collide. There are three ways these form: – Oceanic crust collides with continental crust – Oceanic crust collides with oceanic crust – Continental crust collides with continental crust • With convergent boundaries, subduction can occur. This is when the plate with more density sinks, melts from contact with magma, and can produce volcanoes.

Convergent: Oceanic and Continental • Two features created: volcanic arcs and a deep sea trench, earthquakes • Examples: Cascade and Andes Mountain Ranges

Convergent: Oceanic and Oceanic • Two features created: deep sea trench and a volcanic island arc • Examples: Japan, Alaskan Aleutian Islands, Ring of Fire

Convergent: Continental and Continental • Features: Mountain range and plateaus • Examples: Himalayas in Asia, Ural Mountain Range

Ch 12 Earth Analysis: Date____ Name________ Hr__ Copy and answer in complete sentences 1. What causes Earth’s plates to move? 2. Define Convergent boundaries 3. Define Divergent boundaries 4. Define Transform boundaries 5. Define P(rimary) waves 6. Define S(econdary) waves