The History of Continental Drift and Plate Tectonics

Continental Drift ► Alfred Wegener ► Alfred Wegener published this theory in 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 Drift ► Fit of the continents ► Fit of the continents – the continents look like they could fit together like the pieces of a puzzle. ► Locations of fossils ► Locations of fossils – rare Mesosaurus fossils have been found only in two places on Earth, western Africa, and eastern South America. ► Identical rocks ► Identical rocks – found on the eastern shores of Nova Scotia, Canada, and the western shores of Sweden and the United Kingdom. ► Glacial Striations ► Glacial Striations – matching glacial movement and erosion found in many continental locations where glaciers are not currently present. ► Climate Evidence ► Climate Evidence - due to types of fossils found, coal deposits… continents have been in different climate zones on Earth’s surface

Evidence to Support Continental Drift ► Fit of the continents ► Fit of the continents – the continents look like they could fit together like the pieces of a puzzle.

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

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

Evidence to Support Continental Drift ► Identical rocks ► Identical rocks – found on the eastern shores of Nova Scotia, Canada, and the western shores of Sweden and the United Kingdom.

Evidence to Support Continental Drift ► Glacial Striations ► Glacial 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 Drift ► Climate Evidence ► Climate 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… ► ► 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) ► Global Positioning System (GPS) ► In the 1950’s and 1960’s new technology called Global Positioning System (GPS) allowed scientists to make some important discoveries.

Sea Floor Spreading (1962) ► Mid- Atlantic Ridge ► They found the Mid- 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 Spreading ► Sea Floor Spreading ► Sea Floor Spreading – states that the ocean floor is growing on either side of the Mid Atlantic Ridge. ► Magma ► How it works – Magma moves up through the ridge and cools and hardens into rock.   The sea floor moves apart carrying the continents with it.

Sea Floor Spreading ► Magma ► Magma moves up through the ridge and cools and hardens into rock.

Evidence for Sea Floor Spreading ► Rock Ages younger ► Rock Ages – the rocks of the ocean floor are younger than the rocks of the continents. ► younger ► Also, the rocks near the Mid-Oceanic Ridges are younger 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 Reversals

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

Plate Tectonics ► Plate Tectonics - ► Plate Tectonics - states that the continents were once part of a single landmass called Pangaea.  convection currents  They were moved apart by convection currents in the mantle.

Plate Tectonics ► ► The lithosphere (crust and upper mantle) is broken into 7 large and many smaller plates that float on the plastic mantle. ► convection cellsmolten cooling ► In the upper mantle there are convection cells : rotating circles of molten rock created by heating and cooling in the mantle. ► ► These convection currents are the engine that moves the plates around.

Newest Evidence ► Heat Flow ► Heat Flow – the rocks around the Mid- Oceanic Ridge are hotter than the rocks near the continents.

Newest Evidence ► Earthquakes & volcanoes are NOT randomly located---they mark the location of plate boundaries! ► Shallow Earthquakes occur at mid-ocean ridges and transform boundaries ► Deep Earthquakes occur at convergent boundaries