Plate Tectonics & Continental Drift

10SCIE - Geology

Finn LeSueur

2019

Ngā Whāinga Ako

  • To understand the theory of plate tectonics and Wegener’s theory of continental drift.
  • To describe the evidence to support Wegener’s theory.

What is plate tectonics?

Imagine that there is a pot of soup with pieces of bread floating on top. In this scenario the soup is Earth’s mantle and the bread is Earth’s crust.

Question: What might we observe as the soup boils?

Question: If Earth’s crust is moving, why are we not normally aware of it? What situations are we aware of it in?

Question: What is the effect of the crusts moving apart?

  • This is called a divergent boundary where new crust is generated as the plates separate.

Question: What is the effect of the crusts moving together?

  • This is called a convergent boundary where crust is destroyed as one plate dives under another.

Question: What happens when plates slide past each other?

  • No crust is created or destroyed. The boundary is conservative.

Question: How do the plate boundaries relate to areas of volcanic activity and earthquakes?

Alfred Wegener was a German, born in 1880 and died in 1930. He was a key figure in developing modern ideas around Earth’s structure and movement.

Pangaea

In 1912, Wegener proposed the idea the idea that the continents were once in a different location and once were all together in a super-continent called Pangaea.

He suggested that Pangaea started to break up around 200 million years ago and the pieces drifted apart to form the modern day continents.

Question: Where does the breakup of Pangaea sit in the time-line of Earth’s history?

Wegener was dismissed at the time by geologists for his theory of continental drift because he could not provide an explanation for how the continents were able to move. They had not yet learned about the mantle.

Evidence of Continental Drift

  • Sea floor spreading
  • The continent shapes seem to fit together
  • Similar fossils have been found in South America and West Africa
  • Dating and types of rocks are similar
  • Climate similarities in ancient times

https://www.pbslearningmedia.org/asset/ess05_vid_wegener1/