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.