Test 1 Wk5_Fri

Question 1

Outline the theory of plate tectonics

Answer 1

Plate tectonics is a combination of two theories: Continental drift and seafloor spreading. Continental drift is the idea that continents are continuously moving and have significantly changed positions over millions of years. Seafloor spreading proposes that the middle of the ocean is spreading apart, moving very slowly in opposite directions.

Question 2

Theory of continental drift and supporting evidence

Answer 2

One form of evidence is the similarities in shape between the coastlines if Africa and South America. They fit together like a jigsaw puzzle. In the early 20th century, Alfred Wegener proposed they all fit together into a giant continent named Pangea (supercontinent existing 220 million years ago). More evidence is coastline fit, similar fossils, rocks and landforms created by glaciers in now widely separated continents.

Question 3

The process of seafloor spreading

Answer 3

• Proposed by US geologist Harry Hess.
• Evidence came from discovery of the Mid-Atlantic ridge, a continuous ridge in the middle of the Atlantic Ocean.
• If convection occurs within the Earth’s mantle, then rising hot magma pushes up, creating the ridge splits and moves apart.
• As it is pushed away, tension between the surrounding rocks causing rift zone and shallow earthquakes. As the mantle rock moves away from the ridge crest, it carries the seafloor with it.

Question 4

Describe the main forces that cause plate movement: slab pull, ridge push, gravity and convection currents

Answer 4

Slab pull - Largest force in plate movement. When two plates come together, one is pushed under the other called a ‘subduction zone’. The subducted plate continues to sink. Gravity pulls the front of the plate down causing it to move.

Ridge Push - When 2 plates move apart, magma from the mantle rises up to fill the gap and forms a raised ‘ridge’ in the ocean floor. As this ridge is hot and heavy it expands and pushes the rest of the plate away from the ridge, causing it to move.

Convection – Movement of matter within a fluid. Hotter and therefore less dense material to rise. Colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. Occur in earth’s asthenosphere (upper mantle)

Question 5

Convection Currents in plate movement

Answer 5

With the hot rocks rising and the cooler rocks sinking due to gravity, it causes friction between the movement of rocks and the plate tectonics which can lead to movement

Question 6

Identify the major plates on a world map

Answer 6

• Eurasian
• Indo-Australian
• Antarctic
• Pacific
• North American
• South American

Question 7

Diverging Plate Boundaries

Answer 7

• Plates moving away from each other
• A rift forms (gap)
• Valley forms and mountains may form on outside and streams and rivers may form in a rift
• New tectonic plate may form is fully break away
• Oceanic to Oceanic: When 2 oceanic plates move apart it is seafloor spreading. Crack in ocean floor forms, magma oozes up and forms mid ocean ridge
E.g: The African Plate and the Arabian Plate in the Red Sea.

Question 8

Converging Plate boundaries

Answer 8

• Can occur between two continental plates, a continental and an oceanic plate or 2 oceanic plates
• Continental to continental: forms mountains
• Continental to oceanic: Denser plate will push underneath (subduction) and a trench develops, magma build up and pressure makes a volcano
• Oceanic to oceanic: Same as above with subduction and volcanoes, islands are formed and a line of volcanoes in the ocean
E.g: The Eurasian Plate and the Indian Plate at the Himalayas.

Question 9

Transforming Plate boundaries

Answer 9

• Grind past each other
• Causes a fault/crack in earth’s crust. EG: San Andreas
• Earthquakes are common

Question 10

Landforms that typically occur at each boundary

Answer 10

• Volcanoes
• Mountains
• Narrow lakes or seas

Question 11

Evidence of theory of plate tectonics

Answer 11

• Oceanic plate is newer near oceanic ridge indicating plate moving away from ridge.
• More sediment (dead stuff) on oceanic plate near continental plate.
• Sonar survey by Harry Hess showed ridge existed.

Question 12

Rift Valley

Answer 12

A deep valley that forms as a result of tectonic plates moving apart on land.

Question 13

Define Tectonic Plate

Answer 13

A large layer of solid rock that covers part of the surface of Earth. Movement of tectonic plates can cause earthquakes.

Question 14

Subduction Zone

Answer 14

When oceanic crust collides with continental crust and the oceanic plate sinks below the continental plate.

Question 15

Continental shelves

Answer 15

Underwater cliffs between the beach and ocean.

Question 16

Oceanic crust

Answer 16

Oceanic crust is more dense than the continental crust. It lies beneath the ocean and is roughly 6-7km thick.

Question 17

Continental Crust

Answer 17

Continental crust is less dense than oceanic crust and is floats higher on the mantles. It is the crust under the Earth’s continents. On average it is 35-40km thick and 1500 million years old.

Question 18

Fault

Answer 18

A fracture in rock where the tectonic plates have moved.

Question 19

Mid-oceanic ridge

Answer 19

A series of underwater mountains that form as a result of tectonic plates moving apart and allowing magma to rise to the surface.