Download presentation
Presentation is loading. Please wait.
Published byClaude Evans Modified over 9 years ago
1
The History of Continental Drift and Plate Tectonics
2
Continental Drift ► Alfred Wegener ► Alfred 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:
5
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
6
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.
7
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.
8
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.
9
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.
10
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
11
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
12
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.
13
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.
14
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.
16
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.
17
Sea Floor Spreading ► Magma ► Magma moves up through the ridge and cools and hardens into rock.
18
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.
20
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.
21
Magnetic Reversals
22
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.
24
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.
26
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.
29
Newest Evidence ► Heat Flow ► Heat Flow – the rocks around the Mid- Oceanic Ridge are hotter than the rocks near the continents.
30
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.