Plate Tectonics: The Evidence
- Earth & Space
- Ages 11–14 · Grades 6–8
What you’ll find out
- Fitting coastlines, matching fossils and rocks, and ancient glacier marks suggested the continents were once joined.
- Wegener’s idea of continental drift lacked a mechanism, so many scientists rejected it.
- Sea-floor spreading at mid-ocean ridges, shown by rock ages and magnetic stripes, supplied that mechanism.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
Continents that fit
On a world map, the coastlines of South America and Africa fit together remarkably well, like pieces of a jigsaw. In 1912, a German scientist called Alfred Wegener suggested this was no coincidence. He pointed out that fossils of the same ancient land animals and plants are found on both continents, even though the animals could not have crossed an ocean. Matching rock layers and mountain belts also line up across the Atlantic. Wegener proposed that the continents had once been joined in a single supercontinent and had slowly drifted apart.
Evidence from the sea floor
In the 1950s and 1960s, scientists used new technology to map the ocean floor, and they discovered long underwater mountain chains called mid-ocean ridges. At these ridges, magma rises, cools and forms new sea floor, which slowly spreads outwards on both sides. Rocks near a ridge turned out to be young, while rocks farther away are older, in a matching pattern on each side. This sea-floor spreading finally explained how continents could move, and Wegener’s idea became the theory of plate tectonics.
Curriculum links: NGSS MS-ESS2-3 · England KS3: Earth and atmosphere · Cambridge Lower Secondary Stages 7–9: Earth and space · NCERT Social Science, Classes 6–8