PLATE TECTONICS 1950s scientists first knew earths plates

PLATE TECTONICS

1950’s scientists first knew earth’s plates were moving. Alfred Wegener proposed in 1915 Fossils on different continents match.

Continental Drift 1620 - Sir Francis Bacon maps Atlantic Ocean and notices parallelism of opposite shores 1915 - Alfred Wegener proposes Pangea breaks apart & ocean fills gaps. Based on fossil evidence, rock types and rock structures Magnetic Studies - Outer core generates magnetic field (polarity of North & South Poles). Patterns of polarity reversals in midocean ridge and volcanic rocks where magma reaches surface. magnetic field & seafloor spreading

Youngest rock Oldest rock Mid Atlantic Ridge New ocean crust is being created, pushing continents apart.

Mid Atlantic Ridge Ring of Fire Earthquakes occur along moving plate boundaries. Four plates

Continental plates (crust) generally made of granite. Less dense than oceanic plates Oceanic plates generally made of basalt (more dense & darker) When these two plates meet, oceanic plate is forced under the continental plate.

PLATE BOUNDARIES What happens at each type of boundary? 2 continental plates = Himalayas 2 continental plates = Rift Valley 2 oceanic plates = Islands 2 plates = earthquakes 2 oceanic plates = sea floor spreading (ridge) Practice

Plate visual • http: //www. iris. edu/hq/files/programs/ed ucation_and_outreach/aotm/interactive/ Dynamic. Planet-EQs&Volcanoes. swf

Movement of plates is driven by convection currents. Hot interior of earth rises, cools and sinks.

HOT SPOTS - places where magma is close to surface, but not necessarily at a plate boundary Examples: Hawaii, Yellowstone, Galapagos, Iceland, others.

VOCABULARY Plate tectonics transform boundary convergent boundary divergent boundary rift ridge seafloor spreading magnetic reversal hot spot convection