7 Major plates and dozens of minor plates. It is difficult for scientists to estimate the exact amount

How do they Move? Plates move by floating on top of the Upper mantle (Asthenosphere) The plates move in a certain direction based on the flow of magma beneath them Think of this like a convection oven. Heat rises in the middle, moves outer wards along the crust. It then cools off and sinks back down; the cycle continues

Just like this Pay close attention to how the magma comes up from the center and pulls the plates away from one another. https://www.youtube.com/watch?v=kwfNGatxUJI&list=PL_JoINBzH43MiJhzOG8pOcRUd1S-SoppB&index=4 (Plate tectonics explained)

A history lesson of tectonic plates 1912: Alfred Wegener suggested that North America had once separated from Europe and Africa. Believed all continents were once together forming a “Super continent”. Called it Pangaea. Wegener came up with 4 main pieces of evidence to support his theory of Continental Drift. https://www.classzone.com/books/earth_science/terc/content/visualization s/es0806/es0806page01.cfm?chapter_no=visualization

1st piece of evidence The apparent fit of South America fitting into Africa What are the lighter shaded parts on the map?

2nd piece of evidence Fossils of a number of animals and plants, specifically the mesosaurus, Lystrosaurus, Cynognathus, and Glossopteris All of these fossils have only ever been found on two places on earth, any guesses?

3rd piece of evidence Rocks and mountain ranges Mountain ranges in parts of Eastern North America match those found in the Western European countries Similar in terms of geological makeup and age

4th piece of evidence Past climate data Main focus was on glaciers When glaciers move, they leave scratches are markings on the rocks beneath Glaciers left these markings on rocks found in both the Southern American regions along with the Central African regions. Why would there be glaciers in the tropical areas? Final piece of evidence t hat suggests that these continents were once in cooler climates (perhaps more south) where glaciers actually formed

Downfalls of Alfred Wegener Could not explain how the continents actually moved Suggested it was due to the earth’s rotation He was not taken seriously because he was a meteorologist (atmosphere and weather) and not a geologist (Studies solid and liquid matter on earth).

Hess to the res(cue) Harry Hess was a geologist and in the United States Navy His discovery is known as seafloor spreading and it helped solidify Wegener’s theory of continental drift. Seafloor Spreading: Process by which new oceanic crust wells up in ocean rifts, spreads outward, and sinks into the trenches along the edges of some continents This video should help explain it better. https://www.youtube.com/watch?v=GyMLlLxbfa4 Seafloor spreading with Bill Nye

2 main kinds of plates Continental Crust Between 30-50km thick Used to form continents… pretty straight forward Less dense than Oceanic crust (IMPORTANT) Oceanic Crust Around 7km thick Forms underneath the oceans.. Again, that should be obvious More dense than Continental Crust

This picture may help you understand crust

Types of movement 1. Convergent Boundaries: Occurs when 2 plates come together Subduction Zone (Ocean to Continent): When one plate submerges the other, resulting in a destruction of that plate. Oceanic plate is more dense, therefore it submerges underneath the continental plate.

Subduction zone As the oceanic plate continues underneath the continental plate, it enters the asthenosphere (upper mantle) Turning it into molten which can begin to form mountains or islands. Volcanoes can be caused by the melting of the subducting plate

Converging plates Continent to Continent Collision: Two continental plates come together and force each other upwards. This is how some mountain ranges were formed

Convergent plate Boundaries Convergent boundaries formed the Himalayas. Result of continent to continent

example Andes mountain range resulted from the Nazca plate being submerged by the South American plate

Converging plates Quick Recap When 2 tectonic plates come together (continent to continent, ocean to continent, or ocean to ocean) Can produce volcanoes, and mountain ranges Could also cause earthquakes (more on this later)

Types of movement 2. Diverging plate boundaries: Where 2 tectonic plates are pushed (or pulled) apart from one another. Forms ocean ridges Think of this like a seam on a baseball

Divergent boundaries

How is it formed? Plates pull apart from one another Causes magma from underneath the surface to rise and supercool Lava “stacks” to form underwater mountains Just keeps “snowballing”

How is it formed? Iceland is one place where divergent plate boundaries are above sea level. Absence of lava creates a huge rift in the earth

Mid Atlantic ridge https://www.youtube.com/watch?v=sgDM6m0lUGY https://www.youtube.com/watch?v=bmiuFbQCXDM

Types of movement 3. Transform boundaries: Plates that slide past one another., neither pulling apart of colliding. Think of this as a lateral movement