Continental Drift, Seafloor Spreading & Plate Tectonics Standard 3 (pink test review packet)

Continental Drift Earth’s continents were once joined as single landmass; broke apart and continents drifted to present position Pangaea: supercontinent (break up ~ 200 mya) Wegner Not accepted - lack of mechanism for the movement of continents (why and how)

Evidence for Continental Drift Jigsaw puzzle fit of continents (S.A. & Africa) Rock formations on different continents – same age, similar structure Fossils of land dwelling animals on different continents Climate – coal beds (form in humid swamps) found in Antarctica & tropical plants

Seafloor Spreading New oceanic crust forms at mid-ocean ridges Destroyed at subduction zones (deep-sea trenches) Magma rises, forced upwards, lava fills in ridge, hardens and new seafloor moves away from the center of the ridge.

Evidence for Seafloor Spreading Discovery of mid-ocean ridges Seafloor youngest at mid-ocean ridges Magnetic pattern is the same on both sides of the ridge (mirror image) Hess Technology: Sonar (uses sound waves)

Theory of Plate Tectonics Earth’s crust and rigid upper mantle are broken into tectonic plates Movement of plates creates most volcanoes and major mountain ranges Movements cause earthquakes Plates move because of Convection in the mantle

Types of crust/plates Continental Crust Oceanic Crust Older Lighter Granite 30 miles thick Oceanic Crust Younger Denser Basalt 5 miles thick

Plate Boundaries Divergent convergent transform

Divergent Plates move away from each other Most found on seafloor (mid-ocean ridges) Found on continental crust – stretches crust to form a rift valley (African Rift Valley) Shallow earthquakes

Convergent Plates move towards each other Crash or collide 3 types based on type of crust

Convergent Boundaries: plates converge/collide Continental – continental high mountain ranges Himalayas Continental – oceanic volcanic mountain ranges on land, deep-sea trenches Cold more dense plate sinks Andes, Cascades Oceanic – oceanic volcanic islands, deep-sea trenches Colder, denser plate sinks Mariana Island, Japan

Transform Boundaries Two plates slide past each other Example – San Andreas fault

Mantle Convection Convection: hot less dense material rises & cold, denser material sinks Magma rises because it is less dense than surrounding rock & it forces itself upwards Driving force of plate tectonics

HOT SPOTS Some volcanoes form over hot spots As tectonic plate moves chain volcanoes form Hawaiian Islands – Kilauea located over hot spot Yellowstone located over hot spot