CGC1D PLATE TECTONICS

Theory that helps explain most geologic processes. Earth’s shell is made up of approximately 20 plates (made up of continents and oceans) Plates moving over a weak layer of hot rock.

CONTINENTAL DRIFT Alfred Wegener suggested all earth’s land masses collided 300 million years ago to form one supercontinent He named it PANGAEA.

PANGAEA

WEGENER’S PROOF #1 AND #2 #1 - He saw a jigsaw fit between South America and Africa #2 - Fossils of the same plants and animals on both continents (more similar discoveries were made later)

WEGENER’S PROOF #3 MOUNTAINS OF SIMILAR AGE AND STRUCTURE ON BOTH SIDES OF THE ATLANTIC OCEAN

WEGENER’S PROOF #4 ICE SHEETS COVERED SOUTHERN AFRICA, INDIA, AUSTRALIA & SOUTH AMERICA 300 MILLION YEARS AGO

WEGENER’S MISSING PROOF!  Wegener could not explain what mechanism was powerful enough to move huge continents  Scientists never believed him  J. Tuzo Wilson (Canadian) sparked new interest in continental drift theory  Now known as plate tectonics - includes more than continents – also includes ocean plates

PLATE TECTONICS EXPLAINED THERE ARE 20 PLATES THAT MAKE UP THE EARTH’S OUTER SHELL

PLATE TECTONICS EXPLAINED CONTINUED …  Plates are made up of continental and oceanic crust  They float on a layer of hot rock, several hundred km below the earth’s surface  The plates are likely moved by convection currents

PLATE MOVEMENTS PERHAPS CAUSED BY UNEVEN DISTRIBUTION OF HEAT WITHIN THE EARTH, CAUSING CONVECTION CURRENTS The heat from the core of the earth heats the rock and makes it molten (liquid) The rock closest to the earth’s crust (top layer) is cooler because it is further away from the core(centre)

CONVECTION CURRENTS Continents drifting apart A ridge is a mountain beneath the ocean Continents drifting apart Look at the temperatures!

TYPES OF PLATE MOVEMENTS  Convergent Boundaries – oceanic plate sliding under continental plate or two continental plates pushing against each other (volcanoes and mountain ranges)  Divergent Boundaries – two plates moving in opposite directions (mid-oceanic ridges)  Transform Fault Boundaries – plates slide past each other (earthquakes)

CONVERGENT PLATE BOUNDARIES OCEANIC PLATE MOVES BENEATH CONTINENTAL PLATE AND DISAPPEARS BUT CAUSES MOLTEN MAGMA TO PUSH UP THROUGH VOLCANO AND SOLIDIFIES = DYNAMIC EQUILIBRIUM ( SAME AMOUNT OF ROCK IN EARTH JUST MOVED TO A DIFFERENT PLACE)

DIVERGENT PLATE BOUNDARIES Two plates move in opposite directions and allow a gap for hot magma (liquid rock) to escape upwards As the two plates move apart, the hot magma rises and then cools to form new rock

TRANSFORM FAULT BOUNDARIES Many transform fault boundaries are found on the ocean floor connecting segments of diverging mid-ocean ridges Although transform fault boundaries are not marked by spectacular surface features, their sliding motion causes lots of earthquakes.

CONVERGENT BOUNDARIES (VOLCANOES AND MOUNTAINS)

DIVERGENT BOUNDARIES (OCEANIC RIDGES)

TRANSFORM FAULT BOUNDARIES (EARTHQUAKES)

WHAT DO THE PHOTOS IN THE THIS AND THE NEXT SLIDE HAVE IN COMMON?

PHOTOS CONTINUED

THE PHOTOS SHOW …  That convergent boundaries create volcanoes and mountain ranges  That divergent boundaries create oceanic ridges  That transform fault boundaries cause earthquakes THAT THE EARTH IS MOVING JUST AS ALFRED WEGENER SAID IT WAS!!!!!