Unit 6 - Plate Tectonics - Earth Scienceearthtoleigh.com/earth/documents/keynotes/plate tectonics/6.2 Crustal Activity.pdfevidences needed to validate the Theory of Plate Tectonics.

Crustal ActivityWhat are plate tectonics and how do they a!ect Earth?

Crustal Activity

! Plate Tectonics " the study of the formation and movements of plates

! Plates " section of the lithosphere that moves around

! Lithosphere " Earth’s solid outer crust

! Asthenosphere " partially melted layer that flows slowly and is located below the lithosphere

! Earth’s surface consists of a dozen major plates and some minor ones

! The plates are moving at rates close to 10 cm/year

Crustal Activity

Tectonic Plates

! Convection Currents " driving force of plate movement

! Magma heats up causing it to expand and rise

! Magma cools down causing it to contract and sink

! The plates #solid lithosphere$ are moving on top of the asthenosphere #liquid magma$ due to density di!erences

Crustal Activity

Convection Currents

Crustal Activity

! The idea of continental drift had been around since the early 1900’s, but lacked enough scientific evidence to support the theory

! New advancements after World War II help provide the evidences needed to validate the Theory of Plate Tectonics

Crustal Activity

Earthquake Evidence

! Scientist noticed that earthquakes do not occur at random location, but run throughout the world along isolated belts

! When plotted on a map they outline the plate boundaries

World Earthquakes 1977 " 1999

Crustal Activity

Volcanic Evidence

! Occurs at plate boundaries where plates are interacting

! Ring of Fire " isolated belt around the Pacific Ocean where 90% of the world’s volcanoes exist

Ring of Fire

Crustal Activity

Rock Evidence

! Sedimentary deposits and igneous lava flows are usually placed down in horizontal layers

! Sometimes movement along boundaries causes these layer to tilt or fold

Tilted Rock Layer

Folded Rock Layer

Folded Rock Layer

Mountain Evidence

! As plates collide they sometimes are pushed upward and/or downward

Crustal Activity

Crustal Activity

Mountain Evidence

! Fossilized marine organisms can be found at these high altitudes in the rock