THE CONTINTENTAL DRIFT IDEA WEGENER’S THEORY LESSON 2 1

ALFRED WEGENER  Alfred Wegener was the scientist who proposed the Continental Drift Theory in the early twentieth century. Simply put, his hypothesis proposed that the continents had once been joined, and over time had drifted apart. 2

Before wegener …  Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and in doing so contracted. This was believed to form wrinkles, or mountains, in the Earth's crust. If the idea was correct, however, mountains would be spread evenly over the Earth's surface. We know this is not the case. 3

The continental drift… 4

Pangea e Pantalassa  Some 300 million years ago all the world's land masses were beginning to form into one supercontinent, Pangaea, surrounded by a single universal sea, Panthalassa. 5

The theory of tectonics plate  Plate tectonics is a scientific theory that describes the large-scale motion of Earth's lithosphere.  This theoretical model builds on the concept of continental drift which was developed during the first few decades of the 20th century. 6

evidence for the theory:  The geoscientific community accepted the theory after this concepts: 1. the same types of fossilised animals and plants are found in South America and Africa 2. the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle 3. matching rock formations and mountain chains are found in South America and Africa 7

Accept the theory  In the 1950s, evidence from magnetism in the ocean floor showed that the seafloors were spreading by a few centimetres each year. This showed movement of large parts of the Earth’s crust, now called tectonic plates. 8

There are three kinds of plate tectonic boundaries: 1. Divergent 2. Convergent 3. transform 9

Divergent boundaries:  A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures,frequent earthquakes strike along the rift. Magma from the mantle solidifies into basalt, a dark, dense rocks that underlies the ocean floor. 10

Convergent boundaries:  The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. A chain of volcanoes often forms parallel to the boundary, to the mountain range, and to the trench. Powerful earthquakes shake a wide area on both sides of the boundary. 11

Transform boundaries:  Two plates sliding past each other forms a transform plate boundary. Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. 12

links  HwPR_4mP4 HwPR_4mP4  portal.com/academy/lesson/plate- boundaries-convergent-divergent-and- transform-boundaries.html portal.com/academy/lesson/plate- boundaries-convergent-divergent-and- transform-boundaries.html  portal.com/academy/lesson/alfred- wegeners-theory-of-continental-drift.html portal.com/academy/lesson/alfred- wegeners-theory-of-continental-drift.html 13