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Unit 5 – The Dynamic Earth Chapter 17 – Plate Tectonics. Major focus for the Regents Exam! ESRT pages we will study in this unit: Page 5 – Tectonic Plates Page 10 – Inferred Properties of the Earth Page 11 – Earthquake wave travel time & crust composition. Plate Tectonics.
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Major focus for the Regents Exam!
ESRT pages we will study in this unit:
Plate tectonics is a proven “theory” that describes the formation, movement, and interaction of lithospheric plates over a plastic asthenosphere.
What caused people to consider that the earth’s surface might be moving?
Evidence that we use today to observe plate tectonics for minor crustal movement:
Displaced fossils –
Displaced Strata – Sedimentary rocks found above sea level due to uplift.
Evidence that we use today to observe plate tectonics for major crustal movement:
How can we assume that the processes that occur today…formed the “evidence” that we see from events of the past?
Uniformitarianism – the laws of nature have not changed (ex. Gravity, weathering, erosion and deposition) …”the present is the key to the past”
Where did the theory of plate tectonics start?
1.Similarities in the shape of continents.
2.Mesosaurus (lived about 270 m.y.a) fossils are found in both South America and Africa.
- He used observations above to propose plate movement
- Downfalls of his theory…was he could never explain the mechanism for movement.
1.Fit of Continents (modified from old theory of continental drift ~ Wegner)
2.Glaciation – evidence of glaciation in lower latitudes. (ex. Scratches, glacial erratics, till)
3.Correlation of rocks and mountain ranges on both sides of the Atlantic Ocean.
4.Age of ocean floor (Mid-Ocean Ridge)
5. Magnetic Reversals (Mid-Ocean Ridge)
Plate Boundaries – tectonics plates touch at locations called plate boundaries. There are 3 main types of plate boundaries, based on how the plates are moving in relation to each other.
Continental crust = 2.8 g/cm3
Oceanic crust = 3.0 g/cm3
Convection:the transfer of thermal energy by the movement of heated matter.
Matter is heated = density is decreased = matter rises
Matter is cooled = density is increased = matter sinks
Push – the weight of the uplifted rock at the ridge will push the crust away from the ridge.
Pull – the weight of a subducted plate pulls the rest of the plate down into the Earth.