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continental drift – Hypothesis proposed by Alfred Wegener that states that continents have slowly moved to their current locations on Earth.

seafloor spreading – Theory that magma from below the Earth’s crust is forced upwards toward the surface at a mid-ocean ridge, flows from the cracks as the seafloor spreads apart and becomes solid as it cools, forming new seafloor.

plate tectonics – Theory that Earth’s crust and upper mantle are broken into sections that move around on a plastic-like layer of the mantle (asthenosphere).



Alfred Wegener – German meteorologist who proposed the theory of continental drift.

Harry Hess – Geologist and US Navy Officer who discovered seafloor spreading.


Once-Living Things (evidence for continental drift)

Mesosaurus – a freshwater-swimming reptile whose fossils have been found on the coasts of South America and Africa.

Glossopteris – a tropical fern (type of plant) whose fossils have been found all over the world, even in areas with cold climates.



Pangaea – supercontinent made up of all the continents connected together that broke apart about 200 million years ago.

Panthalassa – world ocean that existed at the time of Pangaea

Laurasia – supercontinent in northern hemisphere made up of North America, Greenland, and Eurasia

Gondwanaland – supercontinent in the southern hemisphere made up of South America, Africa, India, Australia, and Antarctica.


Parts of the Earth

asthenosphere – plastic-like layer of Earth below the lithosphere.  (Behaves much like silly putty.)

lithosphere – rigid outer-most layer of Earth that is about 100 km thick, and is composed of the crust and part of the upper mantle.

plate – sections of Earth’s lithosphere that are composed of oceanic crust, continental crust, and rigid upper mantle that move around on a plastic-like layer of the mantle (asthenosphere).


Reason the Plates Move

convection current – cycle of heating, rising, cooling, and sinking that is thought to be the force behind plate tectonics.


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