Crust Earth’s thin outermost layer. – Continental Crust (land) - thick low density rock (granite). – Oceanic Crust (sea floor)- thin dense rock (basalt)
Lithosphere Earth’s outermost layer Includes the crust and solid upper part of the mantle. Divided into huge pieces called “Tectonic Plates”. “Floats” on top of the asthenosphere - very hot, soft layer of the mantle.
Asthenosphere- Upper Mantle Earth’s thickest layer made of dense iron-rich super heated soft rock. -semisolid layer *Layer where convection currents occur.
Convection Currents in the Asthenospere Causes Sea Floor Spreading – The main cause of plate tectonics Convection Currents – Hot magma rises and cooler magma sinks in the Earth’s upper Mantle
Continental Drift – Theory that the Earth’s continents move over time – Proposed by Alfred Wegener in the early 1900’s – Evidence of Continental Drift: Continents fit together (South America and Africa) Similar fossils found on different continents Similar rocks and minerals Similar climatic conditions
Sea Floor Spreading (divergent boundary) Occurs where tectonic plates spread apart at Mid Ocean Ridges Magma rises from upper mantle creating new crust (sea floor). New “younger” sea floor pushes the existing “older” sea floor out (laterally) explaining why continents move. – Evidence that supports the theory of Continental Drift.
Sea Floor Spreading New crust is formed at mid-ocean ridges spreading the sea floor
Rift Valley (divergent boundary) There are only two rift valleys on Earth within continental crust. -the Baikal Rift Valley and the East African Rift. - Tectonic activity splits continental crust much in the same way it does along mid-ocean ridges. As the sides of a rift valley move farther apart, the floor sinks lower.
Convergent Boundaries Tectonic plates that collide or come together A) When two plates of equal density collide they squish together to form folded non volcanic mountains.
Convergent Boundaries Subduction Zones (a process) B) Difference in density between oceanic and continental crust creates trenches in the ocean and volcanoes on land
Divergent Boundaries Tectonic plates move apart or separate Forms Mid Ocean Ridges in oceans and Rift Valleys on land East African Rift Mid-Atlantic Ridge
Mid-Ocean Ridges Chain of volcanoes at the middle of the ocean floor. Causes Sea Floor Spreading Magma comes up from inside the Earth, cools and hardens and creates new sea floor. The rock at the mid-ocean ridge is the youngest and gets older as it moves farther away from the ridges.