Week 13 · Unit 4 Geological Processes, opener; Lesson 1 Changes in Earth’s Surface: continental drift, tectonic plates and their movements, earthquakes, volcanoes, meteorites · 3 lessons
1
Moving continents: Wegener’s idea
Science Prep 2 Term 1, Unit 4: pp. 82–90
GoalDescribe Wegener’s idea of continental drift and the evidence he used.
New words
continental drift · the idea that the continents slowly move across the Earth’s surfacePangaea · the single land mass that Wegener said existed long agofossil · the remains or traces of a living thing that lived long ago, preserved in rock
Explanation
In 1912 the German scientist Alfred Wegener proposed continental drift. He said that the continents were once joined in one huge land mass, Pangaea, which began to split about 200 million years ago (a rounded figure), and that the pieces have slowly drifted apart to where they are today. His evidence came from three things. First, the coastlines of Africa and South America seem to fit together like pieces of a puzzle. Second, the same kinds of fossils are found on both sides of the Atlantic Ocean. Third, matching rocks are found on both sides. He could not explain what force moves the continents, so many scientists did not accept his idea at first. Later, plate tectonics gave the explanation. Continents do not float like boats on water. A world map is not something we can draw honestly here, so we describe the idea in words and with a flow diagram.
one land mass, Pangaea→splits about 200 million years ago→pieces drift slowly apart→continents of today
Worked examples
The same fossil of a land reptile is found in rocks in South America and in Africa, but the reptile could not swim across an ocean. Wegener said the two lands were once joined.
Why did many scientists doubt Wegener at first? He could not say what force could move whole continents through the rock of the ocean floor. A good idea also needs a good explanation.
Why is it wrong to say that “the continents float like boats”? A boat floats on liquid water, but the continents are parts of solid plates that move over hot, slowly flowing rock below.
Class activity
Torn-paper puzzle. Tear a sheet of old newspaper or scrap paper in two with an uneven tear and move the halves apart. Then fit them back together by the torn edge. Write what this shows about Wegener’s coastline evidence. Then write one thing about the model that is not like real continents (for example, real continents move a few centimetres a year, not at once).
Practice
1
Who proposed continental drift, and in which year?
Alfred Wegener, in 1912.
2
Name the single land mass of long ago.
Pangaea.
3
Give two pieces of evidence that Wegener used.
For example matching coastlines, matching fossils, matching rocks on both sides of the Atlantic.
