Lecture 5: Continental Drift and Plate Tectonics

Question 1

At what time did scientists begin considering the possibility of drifting continents?

Answer 1

Since the 17th century

Question 2

What were the two earliest evidences for continental movement?

Answer 2

The coastlines of the continent (or continental rises) fit together like pieces of a jigsaw
Continents in the southern hemisphere have similar geological histories for the period 350 – 150 Ma

Question 3

What are tillites?

Answer 3

sedimentary rocks deposited when glaciers erode or melt

Question 4

What are striations?

Answer 4

scratch marks left on bedrock the glacier moved over

Question 5

What did tillites and striations indicate?

Answer 5

that massive glaciers covered large parts of the southern hemisphere continents approx. 200 Ma ago

Question 6

What was strange about the striations found onland?

Answer 6

The scratch marks suggested the ice was moving inland, which didn’t make sense with what we know about glaciers

Question 7

How did we explain striations moving inland?

Answer 7

if all the continents were one big continent, then the scratch marks make sense, radiating out from the central, coldest area

Question 8

What do we call the past large landmass in the Southern Hemisphere?

Answer 8

the Gondwanaland continent

Question 9

How did plants and animal fossils give evidence for the continental drift theory?

Answer 9

Certain plant and animal fossils are found across the Gondwanaland continent
These species could not have crossed the present-day oceans

Question 10

What did palaeomagnetism show to back to continental drift theory and how was this explained?

Answer 10

Paleomagnetism of ancient lavas show that the magnetic poles appear to have moved over time
We know that the poles weren’t moving however, the continents moved
As they moved, the alignment of the magnetite within the rocks changed

Question 11

What did Wegener deduce?

Answer 11

All continents once grouped together as Pangea – have since drifted apart like ice floes breaking up

Question 12

What does Pangea mean?

Answer 12

All lands

Question 13

Who created the continental drift theory?

Answer 13

Alfred Wegener

Question 14

How did we think continental drift was driven in 1929?

Answer 14

Subcrustal convection currents

Question 15

Who strongly refuted the Continental drift theory?

Answer 15

Harold Jeffreys

Question 16

When was the Benioff zone discovered?

Answer 16

1954

Question 17

When was the first detailed seafloor maps made and what did they show?

Answer 17

1959 - shows MORs as global system

Question 18

What did Hess propose in 1960?

Answer 18

volcanic origin of seafloor, and seafloor spreading at MORs, driven by mantle convection

Question 19

What proof of seafloor spreading was discovered in 1962?

Answer 19

magnetic stripes as evidence of seafloor spreading

Question 20

When was the sea floor drilled and what did it discover?

Answer 20

1968 - found basalt everywhere

Question 21

When was the plate tectonics theory widely accepted?

Answer 21

Late 1960s

Question 22

What did we confirm related to the tectonic plate theory in the 1990s?

Answer 22

that subduction drives mantle convection – irrelevant of size of the plate