The History of The History of Continental Drift and Continental Drift and

Plate TectonicsPlate Tectonics

Continental Drift Continental Drift

►Alfred WegenerAlfred Wegener published this theory in 1912. It states that the continents were once a single landmass (called Pangaea) that has since separated.

►He gathered evidence to support his idea:

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Fit of the continentsFit of the continents – the continents look like they could fit together like the pieces of a puzzle.

► Locations of fossilsLocations of fossils – rare Mesosaurus fossils have been found only in two places on Earth, western Africa, and eastern South America.

► Identical rocksIdentical rocks – found on the eastern shores of Nova Scotia, Canada, and the western shores of Sweden and the United Kingdom.

► Glacial StriationsGlacial Striations – matching glacial movement and erosion found in many continental locations where glaciers are not currently present.

► Climate EvidenceClimate Evidence - due to types of fossils found, coal deposits… continents have been in different climate zones on Earth’s surface

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Fit of the continentsFit of the continents – the continents look like they could fit together like the pieces of a puzzle.

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Locations of fossilsLocations of fossils – rare Mesosaurus fossils have been found only in two places on Earth, western Africa, and eastern South America.

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Locations of fossilsLocations of fossils – rare Mesosaurus fossils have been found only in two places on Earth, western Africa, and eastern South America.

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Identical rocksIdentical rocks – found on the eastern shores of Nova Scotia, Canada, and the western shores of Sweden and the United Kingdom.

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Glacial StriationsGlacial Striations – matching glacial movement and erosion found in many continental locations where glaciers are not currently present.

Kelly’s Island, Ohio

Evidence to Support Continental Evidence to Support Continental DriftDrift

► Climate EvidenceClimate Evidence - due to types of fossils found, coal deposits… continents have been in different climate zones on Earth’s surface

Unable to Make His Point…Unable to Make His Point…

►No one believed Alfred Wegener because he could not adequately explain how the continents could have moved.

►He died in 1930.

Sea Floor Spreading (1962)

► In the 1950’s and 1960’s new technology called Global Positioning Global Positioning System (GPS)System (GPS) allowed scientists to make some important discoveries.

Sea Floor Spreading (1962)

► They found the Mid-Atlantic RidgeMid-Atlantic Ridge, an undersea mountain range with a steep narrow valley running down the center.

► Because of this discovery they developed a new theory.

Sea Floor SpreadingSea Floor Spreading

► Sea Floor SpreadingSea Floor Spreading – states that the ocean floor is growing on either side of the Mid Atlantic Ridge.

► How it works – MagmaMagma moves up through the ridge and cools and hardens into rock.

The sea floor moves apart carrying the continents with it.

Sea Floor SpreadingSea Floor Spreading► MagmaMagma moves up through the ridge

and cools and hardens into rock.

Evidence for Sea Floor Spreading

► Rock AgesRock Ages – the rocks of the ocean floor are youngeryounger than the rocks of the continents.

► Also, the rocks near the Mid-Oceanic Ridges are youngeryounger than the rocks near the continents.

Evidence for Sea Floor Spreading

► Magnetic Reversals – lava contains tiny magnetized iron minerals that work like compass needles.

When the lava is liquid the minerals line up pointing to the North Pole. When the lava hardens, the minerals are “locked” into position.

When the magnetic poles flip, so do the tiny compass needles.

There are visible matched bands of rocks on either sides of the ridge where the minerals point in the same way.

Magnetic ReversalsMagnetic Reversals

Plate Tectonics

►In the late 1970’s the theories of Continental Drift and Sea Floor Spreading were combined and called the Theory of Plate TectonicsTheory of Plate Tectonics.

Plate TectonicsPlate Tectonics

►Plate TectonicsPlate Tectonics - - states that the continents were once part of a single landmass called Pangaea. They were moved apart by

convection currentsconvection currents in the mantle.

Plate TectonicsPlate Tectonics► The lithosphere (crust and upper

mantle) is broken into 7 large and many smaller plates that float on the plastic mantle.

► In the upper mantle there are

convection cellsconvection cells: rotating

circles of moltenmolten rock created by

heating and coolingcooling in the mantle. ► These convection currents are the

engine that moves the plates around.

Newest Evidence

► Heat FlowHeat Flow – the rocks around the

Mid-Oceanic Ridge are hotter than the rocks near the continents.

Newest Evidence

► Earthquakes & volcanoes are NOT Earthquakes & volcanoes are NOT randomly located---they mark the randomly located---they mark the location of plate boundaries!location of plate boundaries!

► Shallow Earthquakes occur at mid-Shallow Earthquakes occur at mid-ocean ridges and transform ocean ridges and transform boundariesboundaries

► Deep Earthquakes occur at Deep Earthquakes occur at convergent boundariesconvergent boundaries