14.1: What is the evidence for continental drift and plate tectonics?

Question 1

What is the basic structure of the Earth?

Answer 1

The Earth has a concentric structure with three primary layers: the core, the mantle, and the crust.

Question 2

What marks the boundary between the mantle and the crust?

Answer 2

The mantle-crust boundary is marked by the Mohorovičić discontinuity, or Moho, which is about 35 km below continents and 5-15 km below oceans.

Question 3

What are the two layers of the upper mantle?

Answer 3

The upper mantle consists of the lithosphere and the asthenosphere.

Question 4

What is the asthenosphere?

Answer 4

The asthenosphere is a layer of the upper mantle that extends from 100 km to 300 km and flows under pressure.

Question 5

What is the lithosphere?

Answer 5

The lithosphere is a rigid layer above the asthenosphere and varies in thickness.

Question 6

What causes convection currents in the asthenosphere?

Answer 6

Convection currents in the asthenosphere are caused by heat generated deep in the mantle.

Question 7

Who proposed the theory of continental drift?

Answer 7

Alfred Wegener proposed the theory of continental drift in 1912.

Question 8

What was Pangaea?

Answer 8

Pangaea was a large single continent that existed during the Carboniferous period, around 250 million years ago.

Question 9

What geological evidence supports continental drift?

Answer 9

The fit of continents like South America and Africa, glaciation evidence, and similar mountain chains and rock sequences.

Question 10

What biological evidence supports continental drift?

Answer 10

Similar fossils found in different continents, such as marine shellfish in Australia and India.

Question 11

What is palaeomagnetism?

Answer 11

Palaeomagnetism is the ancient record of changes in the Earth’s polarity, observed in ocean floor rocks.

Question 12

What is sea-floor spreading?

Answer 12

Sea-floor spreading is the process by which new oceanic crust is formed at mid-ocean ridges and older crust is pushed away.

Question 13

What are the three types of plate boundaries?

Answer 13

The three types of plate boundaries are divergent (constructive), convergent (destructive), and conservative.

Question 14

What occurs at divergent plate boundaries?

Answer 14

At divergent boundaries, plates move apart, allowing magma to rise and create mid-ocean ridges.

Question 15

What is subduction?

Answer 15

Subduction is the process where a denser oceanic plate is forced under a continental plate at convergent boundaries.

Question 16

What forms at oceanic-continental plate margins?

Answer 16

Ocean trenches and mountain chains, such as the Andes, are formed at oceanic-continental plate margins.

Question 17

What happens at oceanic-oceanic plate margins?

Answer 17

The older, denser oceanic plate subducts, forming trenches and volcanic island arcs.

Question 18

What occurs at continental-continental plate margins?

Answer 18

Little subduction occurs, leading to the formation of mountain ranges like the Alps.

Question 19

What characterizes conservative plate margins?

Answer 19

Conservative plate margins involve plates sliding past each other, causing earthquakes without volcanic activity.

Question 20

What are the characteristics of effusive and explosive eruptions?

Answer 20

Look at textbook, page 491.

Question 21

What is the Push-Pull Theory?

Answer 21

The Push-Pull Theory describes the forces driving plate motions, specifically Ridge Push and Slab Pull.

Question 22

What is Ridge Push?

Answer 22

Ridge Push occurs when hot mantle material is brought to the surface at mid-ocean ridges and is pushed aside by new rising mantle material.

Question 23

What is Slab Pull?

Answer 23

Slab Pull happens when one plate is pushed under another at a subduction zone, and gravity pulls the subducting plate downward.

Question 24

How does mantle convection contribute to plate movement?

Answer 24

Mantle convection occurs in the asthenosphere, helping the plates to move as the subducting plate descends and pushes aside mantle material.

Question 25

What happens to mantle material during the subduction process?

Answer 25

As the subducting plate descends, it pushes aside mantle material, which then moves upward and joins at spreading centers or hot spots.

Question 26

What evidence supports the Plate Tectonic Theory?

Answer 26

Evidence includes continental fit, biological evidence, tectonic activity, geological evidence, and palaeomagnetism.

Question 27

What is the significance of continental fit?

Answer 27

The shapes of continents resemble pieces of a jigsaw puzzle, suggesting they were once joined.

Question 28

What biological evidence supports plate tectonics?

Answer 28

Marsupials are found only in Australia, indicating it drifted away from the supercontinent before predators arrived.

Question 29

What geological evidence indicates plate tectonics?

Answer 29

Glacial deposits found at the equator and coral reef deposits in Antarctica suggest past continental connections.

Question 30

What is palaeomagnetism?

Answer 30

Palaeomagnetism studies the Earth’s magnetic field, which has flipped every 200,000-300,000 years, providing geological evidence.

Question 31

What are Divergent Rift Valleys?

Answer 31

Divergent Rift Valleys are long stretches of land where magma bubbles and volcanic activity create fissures and depressions.

Question 32

What is the formation process of a rift valley?

Answer 32

1. Magma ascends through the asthenosphere. 2. It stretches the crust, creating fissures. 3. Magma breaks through, causing lava flows. 4. The rift sinks, creating a depression. 5. Other landforms like hot springs occur.

eg, The great rift valley that runs from Asia, through the red sea to mozambique. It is a series of continuous depressions that extends for 6000-7000km.

Question 33

How does fossil record evidence support the theory of continental drift?

Answer 33

By demonstrating how similar fossils have been found in completely different areas of the world. For example, marine shellfish fossil evidence has been found in both India and Australia. This demonstrates that at one point these two areas were connected, as the distance between these two places is too far for this type of species to cross. Moreover, these two fossils, although the same species, show different characteristics, indicating that they have evolved in different environments, however used to live in the same one (endemism).

Question 34

How does the existence of similar plant fossil records support continental drift?

Answer 34

The fern between South America and South Africa, reflects how these two continents use to be connected, as plant seeds cannot disperse this far of a distance. The theory of continental drift reflects how tectonic activity has driven plates apart, however, in the future, it is expected that the continents will realign again into another supercontinent.

Question 35

What are convection currents?

Answer 35

Convection currents are cells of hot, ductile magma that rise from the earths outer core, generated by heat deep in the mantle.

Question 36

What do convection currents do in the asthenosphere?

Answer 36

within the asthenosphere, because they are driven by differences in temperature, convection currents drive the direction of plates and the type of plate boundary that is formed between them. Moroeover, the formation of ridge push at divergent plate boundaries is driven by the movement of magma by convection currents in the asthenosphere. As hot plumes of magma rise up to the crust, driven by convection currents, they weaken it and create fissures allowing magma to upwell and push older magma to the side through seafloor spreading.

During slab pull, magma is pushed aside by the subducting plate and convection currents drive the magma up to spreading centres or fissures in the crust.

Question 37

How many years until pangaea reforms?

Answer 37

250 million