Bell Ringer 2/8/2016 Which plate is thicker and less dense? Continental Plate or Oceanic Plate

Earth’s crust is divided into plates. These plates “ride around” on top of the asthenosphere, which is slowly moving solid layer.

Lithospheric plates are not necessarily continents. They can contain the continental crust on a piece of oceanic to make up the plate. Plates move 3-10 cm/year

Convection currents are circulations in the asthenosphere that help move the plates around. Hot, less dense rock rises while cool, more dense rock sinks.

 Earthquakes and volcanoes occurs at plate boundaries where the most tectonic activity is occurring.  Ring of Fire: Area of volcanic activity surrounding the Pacific Mount St. Helens Active Volcanoes Mount St. Helens 2

3 Types of Plate Boundaries 1. Divergent : when two plates spread apart a) Mid-Ocean Ridges: Mountain ranges in the middle of oceans b) Rift Valleys: Deep valleys formed from separating plates Animation

Divergent Boundary: Mid-Ocean Ridge This is occurring in the middle of the Atlantic Ocean, where a chain of underwater mountains is forming. This is where new ocean floor is being formed and the mountain chain is known as the Mid-Atlantic Ridge.

Bell Ringer 2/9/2016 What ocean does the “Ring of Fire” surround?

3 Types of Plate Boundaries 2. Convergent : when two plates collide 3 Types of convergent boundaries

Types of Convergent Boundaries A. Oceanic-Oceanic: When two plates with oceanic crust collide The more dense plate will subduct (sink) beneath the other This forms a trench, or deep valley where the two plates meet Volcanic island arcs form

Types of Convergent Boundaries B. Continental-Continental: when two plates with continental crust collide  Neither plate subducts because both have similar densities  Crust “smushes” together to form mountains Plate Tectonics

Types of Convergent Boundaries C. Continental- Oceanic : When one plate has oceanic crust on it and the other has continental crust on it

The plate with more dense oceanic crust on it subducts beneath the plate with less dense continental crust on it, again forming a trench (deep valley) Mountains form when the continental crust is pushed upward or when magma rises to the surface from the melting oceanic crust in the Earth to form volcanoes.

3 Types of Plate Boundaries 3. Transform : occurs when two plates slip past one another San Andreas Fault

Evidence of Plate Tectonics 1. Earthquakes – occur near plate boundaries 2. Volcanoes – also occur near plate boundaries 3. Puzzle-like fit of the continents

4. Fossils and rocks match up on separated continents in terms of age and origin 5. Mountain Ranges match up on separated continents 6. Similar minerals are found on separated continents

7. Climate record – glacial evidence in the present-day tropics and vice versa › Ex: The southern tip of Africa has glacial evidence

4 Ways that rock layers are changed: 1. Folding: Compression causes layers to bend 2. Tilting: Layer of strata get tipped

3. Faulting: Rocks are displaced along a crack called a fault 4. Uplift: Rock layers get pushed up many meters