Alfred Wegener and Harry Hess This Photo by Unknown Author is licensed under CC BY-SA-NC This Photo by Unknown Author is licensed under CC BY-SA

Wegener A meteorologist, PhD in astronomy Passionate about polar air circulation, polar exploration, and air balloons Noticed east coast of South America fit exactly against the west coast of Africa Claimed the continents once formed a single mass and labeled that “Pangea” which means “whole Earth” This Photo by Unkown Author is licensed under CC BY-S-NC

Wegener and “continental Drift” To prove his theory he used Fossil evidence (tropical plants) Geographical features (mountains) Layers of rock (strata) Claimed mountains formed when edges of drifting continents crumpled

Wegener’s ideas were NOT accepted He was not a geologist-why would anyone believe his theories? Could not prove what immense force was used to split continents Wegener died in 1930 -before his ideas were explored and accepted

Harry Hess Geologist in 1930s During WWII, sounding gear showed what seafloor looked like Bounced sound waves off seafloor to determine depth and features Discovered the following: Bottom of sea not smooth Full of canyons, trenches, volcanic sea mountains Earth’s crust had been moving away on each side of oceanic ridges and were volcanically active which became known as “seafloor spreading”

Seafloor spreading This Photo by Unknown Author is licensed under CC BY

Plate Tectonics Not just continents move, but WHOLE plates of Earth’s crust moves MAY include: A continent Parts of a continent Undersea portions of the crust Earth has 8-12 large plates and 20 smaller ones Move in different directions and speeds

Earth’s tectonic plates This Photo by Unknown Author is licensed under CC BY-SA

So what’s the force that causes continents to move (that Wegener couldn’t prove)? Convection currents in the mantle under the crust!!!!! Although it is solid layer, over geological time, it slowly flows