Plate Tectonics and the Continental Drift Theory - Lec 2 Part 1

Plate Tectonics

➢ the massive, irregularly shaped slabs of rock that make up the Earth’s lithosphere
➢ One plate cannot shift without affecting the others nearby
➢ Plates can move apart, push together or scrape each other

Plate Tectonics Theory

➢ states that Earth’s plates are in slow, constant motion, driven by convection currents in the mantle
➢ Satellites are used to measure plate precisely
➢ 1 – 12 cm per year

Plate Motion over Time

➢ Geologists have evidence that before Pangea existed, other supercontinents formed and split apart over the last billion years

Rodinia

Neoproterozoic Supercontinent

Divergent Boundaries

➢ occurs where plates move apart
➢ Mid-Ocean Ridges
➢ Rift Valleys
➢ Magnetic Stripes
Examples of Divergent Boundaries

Convergent Boundaries

➢ occurs where plates push together
➢ crust either folded or destroyed
➢ Inner-Continent Mountains
➢ Coastal Mountains
➢ Deep-Ocean Trenches (Subduction)
➢ Island Arcs

Continental Collision

➢ occurs when two plates carrying continental crust push together
➢ The folded crust can be pushed up high enough to form mountains

Oceanic Subduction

➢ occurs where one plate with oceanic crust sinks, or subducts, under another plate with oceanic crust
➢ Most are found in the Pacific Ocean

Island Arcs

➢ chains of volcanic islands that form on the top plate, parallel to a deep-ocean trench

Continental Subduction

➢ occurs when ocean crust sinks under continental crust

Deep Ocean Trenches

➢ As the ocean crust moves, it often causes underwater
earthquakes

Coastal Mountains

➢ As oceanic crust sinks under a continent, the continental crust buckles to form a range of mountains parallel to the deep- ocean trench
➢ Cascade Mountains in Oregon and Washington (Mount St. Helen’s)

Transform Boundaries

➢ occurs where plates scrape past each other
➢ crust is neither created nor destroyed
➢ occur mostly on the sea floor near the mid- ocean ridges, but they can occur on land where some are clearly visible as long cracks in Earth’s surface

How Plate Tectonics Helps Geologists

➢ explain Earth’s past and to predict what might happen along plate boundaries in the future
➢ can uncover the history of any region on Earth

Alfred Wegener

➢German meteorologist who proposed the Continental Drift Theory
➢ Continents were once a one large landmass (PANGAEA / PANGEA) 200 MYA

Evidences for Continental Drift Theory

Rock Formation
Fossils
Climate