Plate Tectonics Notes

What is Pangaea?

Pangaea Scientific evidence suggests that all seven of the continents on Earth today used to be connected in a single land mass called Pangaea. Through the process of continental drift, Pangaea broke up, and the individual continents moved away from their placements within Pangaea.

Evidence for Pangaea Alfred Wegener had a theory: Continental Drift. He saw that the continents fit together like a jigsaw puzzle. He then found evidence to support his theory.

Evidence for Pangaea First: Climate clues. He found evidence for glaciers covering the parts of the continents that were normally too hot for ice. Second: Fossil Clues. He found that fossils seemed to jump from continent to continent. Which could only be explained if they were once connected. Third: Rock Clues. He found mountain ranges on different continents with the same age and formation.

Earth 250 Million Years Ago

What is Sea Floor Spreading?

Sea Floor Spreading Plate tectonics is a relatively new scientific concept, combining the earlier theories of continental drift and sea-floor spreading. Sea-floor spreading is the movement of the Earth's crust away from the mid-ocean ridges.

Sea Floor Spreading During the process of sea-floor spreading, hot rock rises up from the mantle and spreads out on the surface to form the ocean floor. As the ocean floor spreads, it pushes the plates around, which in turn move the continents to new locations. A mid ocean ridge is an underwater mountain range. Created by sea floor spreading.

Sea floor Spreading Evidence Normal Polarity – when the compass points North. Reversed Polarity – when the compass points South. Moving away from the mid ocean ridges, there is evidence that shows the changing of polarity. This shows that the plates are moving away from each other. Since they are pushing away from each other, they must be taking the continents with them.

The map below shows the locations of the Earth's mid-ocean ridges, which are the sites of sea-floor spreading.

So what is a Plate Tectonic?

Glad You Asked! Imagine the “shell” of earth. It is cracked like a boiled egg. These pieces of the lithosphere float on the asthenosphere, and they move and bump into each other.

Plate Tectonics The scientific theory that explains the movements of the continents is called plate tectonics. The word "plate" is used to describe large, brittle blocks of the Earth's surface which appear to move upon the Earth's mantle as large pieces. The word "tectonics" comes from the Greek word that means "to build." At the places where two plates meet, constructive (building) or destructive (tearing down) processes may take place. Some of those processes will be discussed in these notes.

What are the Types of Boundaries?

Plate Boundaries Convergent – when the plates are pushing into each other. Divergent – when the plates are moving away from each other. Transform – when the plate are moving past each other and scraping. Subduction: at a convergent boundary, the less dense plate goes under the more dense plate.

What causes the movement?

Convection Remember that convection is the flow of heated material. Hot material flows up, and cooler material flows down. Same thing happens in the asthenosphere.

How do the plates move? Basal drag – the convection current drags the plate. Ridge Push – at the mid ocean ridge, it will push up and across, moving the plate. Slab Pull – As a slab sinks, it will be pulled down by the convection current.