Evidence for Continental Drift

Take a look at a map of Earth’s surface. Look carefully at

the shape of each continent. The continents look like they

might fit together like pieces of a puzzle, don’t they? People

throughout history have noticed this and wondered what it

meant. For example, over 400 years ago Abraham Ortelius, a

Dutch mapmaker, noticed that the coastlines of South

America and Africa fit together.

 

Have you ever been to Pangaea?

In 1912, a German scientist named Alfred Wegener

(VEG nur) proposed that the continents did at one time fit

together. He suggested that all the continents were once

connected. Wegener said they were once one big landmass.

He called this landmass Pangaea (pan JEE uh), which

means “all land.”

According to Wegener, about 200 million years ago, Pangaea

broke into pieces. The pieces drifted away from each other.

We call these pieces continents. Wegner’s hypothesis is called

continental (kahn tuh NEN tul) drift. Continental drift is

the hypothesis that Pangaea broke apart into continents that

moved slowly to where they are today. So even though you

haven’t visited Pangaea, the area where you live probably

was part of Pangaea millions of years ago

 

Did everyone accept Wegner’s idea?

Wegener’s hypothesis on continental drift was a

controversial idea. It caused a lot of argument. Wegener

didn’t convince people that his ideas were right during his

lifetime. He didn’t have enough evidence. For example, he

couldn’t explain what made the continents drift. He thought

Earth spinning on its axis might cause the continents to

plow through the ocean floor. But geologists and physicists

of that time rejected this explanation. Wegener’s basic idea

wasn’t accepted until long after his death in 1930. More

evidence came later to support his ideas.

 

How do animal fossils support continental drift?

Animal fossils offer one clue that the continents might

have been joined together millions of years ago. Fossils are

the remains, imprints, or traces of prehistoric organisms.

Fossils can tell when and where organisms once lived and

how they lived. For example, fossils of Mesosaurus have been

found in South America and in Africa. Mesosaurus is a

reptile that lived on land and in fresh water. How could this

reptile move between two continents separated by a salty

ocean? It is not likely that it swam across the Atlantic

Ocean. Wegener’s hypothesis of continental drift proposes

that Mesosaurus lived on both continents when they were

joined together. The map on the next page shows where

fossil remains of different animals have been found on

different continents.

 

How do plant fossils support continental drift?

Another fossil that supports continental drift is

Glossopteris (glahs AHP tur us). Fossils of this plant are

found on five continents—Africa, Australia, Asia, South

America, and Antarctica. Finding Glossopteris in so many

areas supported the idea that all of these regions once were

connected and had similar climates.

 

What do climates tell us about continental drift?

Scientists have found fossils of warm-weather plants on

the island of Spitsbergen in the Arctic Ocean. This is one of

the coldest places on Earth. How did this happen? Wegener’s

hypothesis of continental drift proposes that Spitsbergen

Island drifted to the Arctic from a tropical region of Earth.

 

How do rocks support continental drift?

Glaciers are large, slow moving bodies of ice on land.

Glaciers leave tracks as they move, scouring and polishing

rock surfaces under them. They also leave deposits of glacial

rock and sediment. Glaciers are found in cold areas. Yet

there are traces of glaciers and deposits in many tropical

and temperate regions of Earth. How is this possible?

Wegener’s hypothesis of continental drift says that millions

of years ago, some tropical and temperate lands had cold

climates and were located near Earth’s south pole. These

continents were joined together and partly covered with ice.

When the continents drifted apart into warmer climates, the

glaciers melted away from these areas. The glacial deposits

left behind add more evidence to support continental drift.

What do rocks tell us about continental drift?

 

If the continents were connected at one time, then the

rocks located where the land broke apart should be similar.

Similar rock structures are found on different continents.

For example, rock structures found in the Appalachian

Mountains of the eastern United States are similar to rock

structures found in Greenland and western Europe. Some

rock structures from eastern South America are similar to

rock structures in western Africa. Rock clues like these

support the idea that the continents were connected in the

past.

 

How could continents drift?

Wegener used clues found in rock, fossil, and climate to

support his hypothesis of continental drift. The computer

model below shows how the continents might have drifted

over millions of years. But Wegener was not able to explain

why the continents broke apart. Most importantly, he could

not explain what caused the continents to drift. Wegener

hypothesized that the continents plowed through the ocean

floor. He thought that the spinning of Earth on its axis

might have been the cause. He couldn’t prove his ideas with

facts. Physicists of his day thought he was wrong. The idea

was rejected because it was too unusual.

Today, there is more evidence for continental drift. After

Wegener’s death, new technology provided new evidence.

New ideas about continental drift were developed. One of

these ideas is called seafloor spreading. You’ll read about this

in the next section.