Download Tectonic Plates

Tectonic Plates •  Tectonic Plates: Pieces of the lithosphere that move on top of the asthenosphere •  Made of the crust and the rigid (s8ff), outermost part of the mantle •  Each tectonic plate fits together with the tectonic plates that surround it like pieces of a puzzle Tectonics Up Close Colliding Con1nents Movie Wegener’s Con1nental Dri8 Hypothesis •  Con1nental Dri8: the hypothesis that states that con8nents once formed a single landmass, broke up, and driCed to their present loca8ons. •  Scien8st Alfred Wegener developed the hypothesis in the early 1900s. hKp://www.youtube.com/watch?v=1‐HwPR_4mP4 Pangaea •  Wegener theorized that all con8nents used to be a single, huge con8nent he called Pangaea. •  Pangaea is Greek for all earth. •  Pangaea existed 245 million years ago.
Sea‐Floor Spreading •  Evidence to support the con8nental driC hypothesis comes from sea‐floor spreading. •  Sea‐floor spreading is where new oceanic lithosphere forms as magma rises toward the surface and solidifies.
Mid‐Ocean Ridges & Sea‐Floor Spreading •  Mid‐Ocean Ridges: underwater mountain chains that run through Earth s ocean basins. •  Occur where sea‐floor spreading takes place.
Evidence for Sea‐Floor Spreading •  Throughout Earth s history, the north and south magne8c poles have changed places many 8mes (scien8sts aren’t sure why or even exactly how!). • Magne1c Reversals are recorded in the ocean floor, which also shows that the sea floor is spreading out. Magne1c Reversals •  Magma at mid ocean ridge carries 8ny grains of magne8c minerals that act like compasses. •  These minerals align with the current magne8c field of the Earth. When the Earth s magne8c field reverses, the magne8c mineral grains align in the opposite direc8on. • Geologists observe how/when the magne8c field of Earth changes, by observing different polari8es of the minerals Mechanism for Movement •  Convec1on Currents in the mantle are responsible for sea‐floor spreading, which also effects other plate movements • hIp://www.youtube.com/watch?v=ryrXAGY1dmE 13 Major Plates 1.  North American 2.  Juan de Fuca 3.  Caribbean 4.  Cocos 5.  Nazca 6.  South American 7.  Eurasian 8.  Arabian 9.  African 10.  Indo‐Australian 11.  Philippine 12.  Pacific 13.  Antarc8c ** There are also more than a dozen minor plates ** Tectonic Plate Movement •  Tectonic plates float on the asthenosphere. • Any 8me two plates touch, that is called a plate boundary • Three types of boundaries: • Convergent • Divergent • Transform Plate Boundaries Rap Convergent Boundary •  Places where plates collide together •  Just like a car crash, when plates collide, they get deformed • The type of deforma8on depends on the density of the plates
Example •  Dense oceanic plate bends down deep into the Earth (subduc8on) • Less dense con8nental plate folds up into a mountain • A trench forms at the “elbow” between them
Possible Convergent Boundaries ** Remember: Oceanic crust is denser than Con7nental crust ** • Oceanic + Con1nental = oceanic plate sinks beneath the con8nental plate; called subduc1on • Oceanic + Oceanic = the denser plate dives under the other and returns to the mantle; magma rises forming volcanoes • Con1nental + Con1nental = neither is dense enough to subduct, so they squeeze up into a mountain
Divergent Boundary •  Places where plates move away from each other • In the oceanic crust: cracks get filled in with magma from the asthenosphere, forming a ridge • In the con8nental crust: land between the cracks drops down and forms a riC valley RiC Valley ‐ Kenya Transform Boundary •  Places where plates slide past each other in opposite direc8ons • Built up energy from the plates pushing against each other is finally released in one large “slip” of the plates, causing an earthquake Boundary Summary