Chapter 10 Section 1 Notes Continental Drift

Like a Puzzle Similarity of the continental shorelines on either side of the Atlantic ocean.

Like a Puzzle The east coast of South America seems to fit perfectly into the west coast of Africa.

Alfred Wegener In 1912, a German scientist hypothesized that the continents once formed part of a single landmass called a supercontinent.

Alfred Wegener The supercontinent began breaking up into smaller continents about 250 million years ago (during the Mesozoic Era).

Alfred Wegener Over millions of years these continents drifted to their present locations.

WEGENER’S EVIDENCE Fossil Evidence Fossils of the same plants and animals were found in both South America and western Africa.

WEGENER’S EVIDENCE Fossil Evidence Fossils of the Mesosaurus, a small, extinct land reptile, are found in both South America and western Africa.

WEGENER’S EVIDENCE Fossil Evidence It was unlikely that these reptiles had swam across the Atlantic ocean.

WEGENER’S EVIDENCE Rock Formations The ages and types of rock in western Africa and in eastern South America match closely.

WEGENER’S EVIDENCE Rock Formations Mountain chains that ended at the coastline of one continent continue on other continents across the ocean.

WEGENER’S EVIDENCE Rock Formations The Appalachian Mountains extend northward along the eastern coast of North America and are of similar age and structure of mountains in Greenland, Scotland, and northern Europe.

WEGENER’S EVIDENCE Climatic Evidence Changes in climatic patterns suggest that the continents have not always been located where they are now.

WEGENER’S EVIDENCE Climatic Evidence Geologists have found layers of debris from ancient glaciers in southern Africa and South America.

WEGENER’S EVIDENCE Climatic Evidence Fossils of tropical plants have been found in areas that now have colder climates.

WEGENER’S EVIDENCE Missing Mechanisms Other scientists of the time rejected the mechanism by which Wegener proposed that the continents moved.

WEGENER’S EVIDENCE Missing Mechanisms Wegener suggested that the continents plowed through the rock of the ocean floor.

WEGENER’S EVIDENCE Missing Mechanisms There was no geologic evidence supporting Wegener’s idea that the continents plowing through the ocean floor. Wegener died in 1930 never founding an acceptable mechanism.

Mid-Ocean Ridges What are they? Undersea mountain ranges through the center of which run steep narrow valleys.

Mid-Ocean Ridges 1st trend: The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge.

Mid-Ocean Ridges 2nd trend: The ocean floor is youngest at the mid-ocean ridges and grow older as you mover farther away from mid-ocean ridges. Rocks on land are as old as 3.8 billion years old, while the oldest oceanic rocks are only 175 million years old.

Sea-Floor Spreading In the 1950’s, Harry Hess suggested that the valley at the center of the ridge was a crack in Earth’s crust where new sea floor was being created

Sea-Floor Spreading Hess suggested that if the ocean floor is moving, the continents must be moving too. He thought that sea-floor spreading was the mechanism that Wegener had failed to find.

Paleomagnetism As magma solidifies to form rock, iron-rich minerals in the magma align with Earth’s magnetic field in the same way that a compass needle does.

Paleomagnetism When the rock hardens, the magnetic orientation of the minerals becomes permanent. This residual magnetism of rock is called paleomagnetism.

Magnetic Reversals Earth’s magnetic field has not always pointed north. Rocks with magnetic fields that point north are normal polarity, while rocks with magnetic fields that point south are reversed polarity.

Magnetic Reversals There is a pattern of normal and reversed polarity in the rocks of the ocean floor. Scientists used this pattern to create the geomagnetic reversal time scale.

Magnetic Symmetry The striped magnetic pattern on one side of a mid-ocean ridge is a mirror image of the striped pattern on the other side of the ridge.

Magnetic Symmetry The patterns indicate that the youngest rocks are at the center of a ridge and the older rocks are farther away on either side of the ridge.

The End !!!