Denser material sinks Less dense material rises to the top
Crust: Thick layer of cool rock, surrounding earth. There are 2 types: oceanic and continental Mantle: Earth’s thickest layer, 1700 miles thick, hot rock, less dense than core Outer Core: Layer of liquid metal that surrounds inner core Inner Core: Ball of solid, hot metal
Continental Drift Hypothesis proposed by Alfred Wegener in 1912Alfred Wegener Earth’s continents were once joined in a single landmass and gradually moved apart.
Fossils: mesosaurus found in South America & Western Africa – not found anywhere else! Climate: evidence of change: Warm weather plants in Greenland, glacial evidence in South Africa Geology: rocks from Brazil match those of Western Africa, Limestone of Appalachian mountains matches Scotland’s highlands
Pangaea: Greek meaning “all lands” Pangaea: Giant continent that reached from pole to pole and covered area where Africa lies today
In the mid 1900’s scientists proved that tectonic plates move. Built upon Wegener’s ideas.
Mid Ocean Ridges: huge underwater mountain ranges Mid Ocean Ridges ◦ Sea Floor Spreading – ridges form along cracks in the crust, molten rock rises through the cracks making new crust ◦ Age of sea floor – sea floor is youngest at the ridges, older farther away ◦ Ocean trenches – deep canyons where the sea floor is sinking into asthenosphere.
Convection: energy transfer by the movement of material Convection current: sinking and rising motion that transfers heat in a material
Divergent boundaries: occurs where plates move apart – most are found in the ocean Convergent boundaries: occurs where plates push together Transform boundaries: occurs where plates scrape past each other
AKA spreading centers Rift valley: deep valley formed as tectonic plates move apart, as a long a mid-ocean ridge
Mid-ocean ridges are the longest chains of mountains on Earth Mid-Atlantic ridge world’s longest mountain range
Earth’s magnetic poles switch places, called magnetic reversals How stuff worksstuff
Like the sea floor, continents can split apart at a divergent boundary Great Rift Valley
One plate of oceanic crust subducts (sinks) beneath another plate of oceanic crust Older plate is colder and denser, and sinks below younger plate Creates two features: ◦ Deep ocean trenches – deep canyons in ocean floor example: mariana trench ◦ Island arcs – chains of volcanic islands that form on the top plate parallel to trench. Example: Japanese islands
Ocean crust sinks under continental crust Oceanic crust is colder and denser than continental crust Features created: ◦ Deep ocean trenches – can cause underwater earthquakes ◦ Coastal Mountains – Examples: Cascade Mountains
The plates lithosphere has been in motion for millions of years By studying rock layers geologists can uncover the history of any region. Plate tectonics gives scientists a way to study and predict geologic events such as earthquakes and volcanic activity