Chapter 10: Plate Tectonics

Section 1: continental drift As people studied maps they were impressed by the fact both sides of a continent fit together

Wegener’s hypothesis In 1912 Alfred Wegener proposed a hypothesis called continental drift which states at one time there was a supercontinent.

Fossil evidence There are Mesosaurus fossils in both South America and Western Africa. These reptiles would probably not have swam across the ocean so at one time the land was connected.

Rock formation evidence The ages and types of rocks in coastal regions of widely separated areas such as Western Africa and eastern South America closely match.

Climatic evidence Plant fossils indicate tropical areas that are now much cooler. Layers of debris of ancient glaciers are in Southern Africa and South America.

Mid-ocean Ridges 1947 scientists mapped out the Mid-Atlantic Ridge which is part of an undersea mountain range with a narrow valley in the middle. Sediments and rocks closer to the ridges are younger than those farther away. Ocean floor rocks are only 200 million years while some continent rocks are 4 billion years old.

sea floor spreading Sea Floor Spreading – valley at the center of the ridge is where magma rose and filled in the region. This process was confirmed with paleomagnetism – the study of the magnetic properties of rocks.