Commotion Beneath the Ocean Introduction to Plate Tectonics

Plate Tectonics Originally proposed by Wegener - but ridiculed !! 1960’s new evidence found Earth’s Surface Continually Shifting Plate - Large, Rigid Slab of Solid Rock Tectonics- to build

Theory of Continental Drift Pangaea –225 mya Earth/Solar System bya Life –3.4 bya

Evidence of Continental Drift Coastline shapes Rocks Minerals Fossils

Inside the Earth Crust Mantle Core

Convection Heated material expands - becomes less dense - more buoyant It rises and cold material takes it’s place

Heat Decay of Radioactive Elements inside Earth Trying to Escape Convection - transport of mass by heat (heat changes the density)

Mid- Ocean Ridges Sonar Mapping Began during WWII By 1960’s clear maps of mid ocean ridges

Ocean Maps All the major oceans have long ridges

Underwater Volcanoes Opening of the earth where hot molten rock, ash, and gases to escape from deep below the surface Underwater volcanoes are called Hydrothermal vents

So what do the ridges have to do with plate movement? Undersea volcanoes Deposit molten rock from mantle convection Seafloor spreading - Supported Theory of Plate Tectonics Harry Hess

Seafloor Spreading as proposed by Harry Hess New Ocean Floor deposited at the ridges Moves laterally away from the ridges Moves back down at the continental margin Continents are not “islands” they are parts of larger plates that move on the soft asthenosphere

Earth’s Magnetic Field Liquid Iron in the outer core Moving Electrical charges (current) INDUCE a magnetic field Aligns approximately with the spin axis but periodically flips N S

Evidence for Seafloor Spreading Magnetic Reversals Rocks have magnetic fields When rocks cool magnetic minerals align to Earth’s Mag Field 1960’s drilling found Mirror images on each side of mid Atlantic ridge

How old is the lithosphere? Dates of rock increased on both sides of mid-ocean ridges

The Plates Earth - egg Shell - cracked, but stronger than the interior Tectonic plates - in the lithosphere

Plates Tectonic plates are in the lithosphere The lithosphere floats on the Asthenosphere Asthenosphere is undergoing convection Plates are moving and interact with other plates

Plate Boundaries Transform Divergent Convergent

Divergent Plates Lithosphere is being produced Happens at mid ocean ridges Plate motion is away from the boundary Sea-floor spreading Well if two plates are diverging…..

Convergent Boundaries Lithosphere sinks back into the asthenosphere (its recycled) One plate moves under another plate - SUBDUCTION The ocean plate is denser !!

Continent - Continent When two continental crusts converge, the result is a huge mountain range. Both pieces of crust are buoyant. Example - Himalayas Indian plate -->> Asian plate. Numerous earthquakes but very little volcanism.

Transform Plate Boundaries One plate slides parallel to another plate San Andreas Fault

Plate boundary details for the West Coast of North America

Divergent Plate Boundaries

Hot Spots and Hawaiian Islands 1963 Tuzo Wilson (also discovered transform faults) Noticed Volcanism in some areas active for a really long time Heat produced magma, melted through the plates. Magma lighter than the rock rises.

Hawaiian Chain

Hot Spots

Measuring Hot Spots Yellowstone Plate moves Hotspot does not Determine and compare the age of the rocks New evidence shows that hot spot may also move somewhat

Hot Spots Yellowstone: several craters or calderas Energy fuels hot springs and geysers - Old Faithful May be a Super Volcano !!

Review