Topic 4 - Plate Tectonics

Question 1

Focus 2
What is the geological time scale?

Answer 1

The Geological Time Scale is used by earth scientists to place broad ages on events that have occurred in the past.

Question 2

Focus 2
Describe the geological time scale: eons.

Answer 2

Eons are very long periods of time subdivided into eras.
Archean (4.0 - 2.5 billion years ago)
Proterozoic (2.5 billion years ago - 538.8 million years ago)
Phanerozoic (538.8 million years ago - present)

Question 3

Focus 2
Describe the geological time scale: eras.

Answer 3

Eras are in turn subdivided into periods.
Palaeozoic (538.8 - 251.9 million years ago)
Mesozoic (251.9 - 66.0 million years ago)
Cenozoic (66.0 million years ago - present)

Question 4

Focus 2
Describe the geological time scale: periods.

Answer 4

Cambrian (538.8 - 485.4 million years ago)
Ordovician (485.4 - 443.8 million years ago)
Silurian (443.8 - 419.2 million years ago)
Devonian (419.2 - 385.9 million years ago)
Carboniferous (358.9 - 298 million years ago)
Permian (298.9 - 251.9 million years ago)
Triassic (251.9 - 201.4 million years ago)
Jurassic (201.4 - 145 million years ago)
Cretaceous (145.0 - 66 million years ago)
Paleogene (66.0 - 23.03 million years ago)
Neogene (23.03 - 2.58 million years ago)
Quaternary (2.58 million years ago - present)

Question 5

Focus 3
Describe continental drift.

Answer 5

Continental drift is a theory that explains how continents shift positions on Earth’s
surface.
Continental drift explains why look-alike animal and plant fossils and similar rock
formations are found on different continents.
Throughout history, the movement of the tectonic plates has shaped the surface of the Earth.
These tectonic plate movements continue today, often with devastating consequences for communities.

Question 6

Focus 3
Earthquakes:
Define earthquake.

Answer 6

Earthquake – the sudden violent shaking of the group, typically causing great destruction, as a result of movements within the earth’s crust

Question 7

Focus 3
Earthquakes:
Define fault.

Answer 7

Fault – a fracture or zone of fractures between two blocks of rock (which allow the blocks to move relative to each other)

Question 8

Focus 3
Earthquakes:
Define epicentre.

Answer 8

Epicentre – a point on the surface of the Earth that is directly above the focus of an earthquake

Question 9

Focus 3
Earthquakes:
Define focus / hypocentre.

Answer 9

Focus/hypocentre – subsurface point at with the energy stored along a locked fault is first released (where fault rapture commences)

Question 10

Focus 3
Earthquakes:
Define seismic wave.

Answer 10

Seismic wave – mechanical wave/vibration generated by an earthquake, explosion, or similar energetic source that travels through the Earth or along its surface

Question 11

Focus 3
Earthquakes:
Define aftershock.

Answer 11

Aftershock – lower-magnitude earthquakes that follows the main shock of a larger earthquake in the same general area during the following days - years

Question 12

Focus 3
Earthquakes:
Define liquefaction.

Answer 12

Liquefaction – process by which water-saturated sediment temporarily loses strength and acts like a fluid (caused by earthquake shaking)

Question 13

Focus 3
Earthquakes:
How do scientists find evidence of previous earthquakes?

Answer 13

Scientists look for layers of the same type of rock or sediment that are displaced across a fault to find evidence of previous earthquakes in the ground
By measuring the displacement and dating the rock, scientists can identify the ages of past earthquakes.

Question 14

Focus 3
Earthquakes:
How do earthquakes cause tsunamis?

Answer 14

If big enough and close enough the ocean floor, the energy from an earthquake can cause the ocean floor to suddenly rise (uplift) and fall (subside)
This sudden vertical displacement of the ocean floor as it rises or falls causes the water above it to rise or fall consequently, resulting in a tsunami.

Question 15

Focus 3
Earthquakes:
What is magnitude?

Answer 15

An earthquake has one magnitude which does not depend on where the measurement is made; magnitude scales measure the size of the earthquake at its source.

Question 16

Focus 3
Earthquakes:
What is intensity?

Answer 16

An earthquake causes many different intensities of shaking in the area where is occurs; intensity scales measure the amount of shaking at a particular location
The amount of damage caused by an earthquake depends on its location
Earthquakes that occur beneath the ocean may not even be felt on land
Earthquakes that occur in densely populated areas will cause significantly more damage than in remote areas.

Question 17

Focus 3
Earthquakes:
Where do earthquakes occur?

Answer 17

Earthquakes mainly occur along tectonic plate boundaries – fault lines
For example, most large earthquakes occur around the edges of the Pacific Ocean where the Pacific Plate is being subducted beneath the surrounding tectonic plates
This area is known as the “ring of fire” .

Question 18

Focus 3
Volcanoes:
How do volcanoes occur?

Answer 18

Convergent plate boundaries (where two tectonic plates collide and one moves below the other) would cause the release of magma & the formation of volcanoes
This would occur at oceanic plate boundaries – oceanic plates are denser and thinner and therefore would be subducted beneath a lighter and thinner continental crust.

Question 19

Focus 3
Fold Mountains:
How do fold mountains occur?

Answer 19

When two continental plates collide, neither plate moves under the other because the continental rocks are relatively light and instead the crust buckles and is pushed upward or sideways
Mountain ranges are formed as a result of this eg. Himalayas

Question 20

Focus 3
Describe sea floor features:
Mid-ocean ridges.

Answer 20

A mid-ocean ridge is a seafloor mountain system which takes place when seafloor spreading occurs as a result of divergent (ocean) plate boundaries.

Question 21

Focus 3
Describe sea floor features:
Trenches.

Answer 21

At a convergent (ocean - continent) plate boundary, an ocean trench is created where the oceanic plate subducts under the continental plate.

Question 22

Focus 3
Describe sea floor features:
Paleomagnetic striping.

Answer 22

Paleomagnetic stripes are the result of the reversal of the Earth’s magnetic field as well as seafloor spreading.
The formation of new oceanic crust and rocks through seafloor spreading becomes magnetised in stripes of varying widths due to changes in the Earth’s magnetic field (from “normal” to “reversed”)
The widths of these stripes depend on how long the Earth’s magnetic field remains in one position and how fast the seafloor is spreading.
Seafloor spreading is a result of divergent oceanic boundaries (where oceanic plates move away from each other)

Question 23

Focus 3
Describe sea floor features:
Seafloor age distributions.

Answer 23

Sea floor age distributions occur at divergent oceanic plate boundaries where new crust is formed. The ages of rocks at these boundaries can provide information regarding how long the spreading has occurred and how fast the plates are moving apart.

Question 24

Focus 3
Describe the Hawaiian-Emperor Volcanic Island Sea Chain.

Answer 24

The Hawaiian-Emperor Volcanic Sea Chain is an example of a seamount and island chain created by a hot spot.
Hot spots are fixed points across the Earth’s surface where magma rises up until it erupts on the surface – this can create volcanoes in the middle of a tectonic plate.
The Hawaiian Islands were formed by a hot spot occurring in the middle of the Pacific Plate. While the hot spot itself is fixed, the plate is moving. So, as the plate moved over the hot spot over millions of years, the string of islands that make up the Hawaiian Island chain were formed.

Question 25

Focus 3 Describe the Galapagos Islands.

Answer 25

Galapagos is located on the Nazca tectonic plate, which is continuously moving eastward over the Galapagos hot spot and has formed the chain of islands. This geographic movement is correlated to the age of the islands, as the eastern islands (San Cristóbal and Española) are millions of years older than the western islands (Isabela and Fernandina). The islands were formed through the layering and lifting of repeated volcanic action. Most of the islands have a distinctive conical shape that is often associated with volcanic action. Each major island, with the exception of the largest island, Isabela, consists of a single large volcano. Isabela was formed when six volcanoes joined above sea level. Geologically, the Galapagos Islands are quite young, probably no more than five million years old. Some of the westernmost islands, which are the most volcanically active, may only be hundreds of thousands of years old and are still being formed today.

Question 26

Focus 4 Plate Tectonics: Explain Divergent (ocean) plate boundaries.

Answer 26

Oceanic plates moving away from each other. This divergent boundary is considered constructive since new crust is formed Magma from the mantle underneath the crust to rise up the surface to cool and solidify at the plate boundary.

Question 27

Focus 4 Plate Tectonics: Divergent (ocean) plate boundaries & types of tectonic events

Answer 27

Forms new seafloor (sea-floor spreading) Forms long chains of mountains on the ocean floor (oceanic ridge). E.g. The Mid-Atlantic Ridge

Question 28

Focus 4 Plate Tectonics: Explain Divergent (continent) plate boundaries.

Answer 28

Continental plates moving away from each other. As the plates separate along the boundary, the block between the faults cracks and drops down. Sinking of the block forms a central valley (rift valley). Magma seeps upward to fill the cracks. In this way, new crust is formed along the boundary.

Question 29

Focus 4 Plate Tectonics: Divergent (continent) boundaries & types of tectonic events.

Answer 29

Sinking of the block forms a central valley (rift valley). Central/rift valleys. E.g. Great Rift Valley, Africa

Question 30

Focus 4 Plate Tectonics: Explain Transform plate boundaries.

Answer 30

Plates sliding horizontally next/past to each other Most transform faults are found on the ocean floor, however a few do occur on land.

Question 31

Focus 4 Plate Tectonics: Transform plate boundaries & types of tectonic events.

Answer 31

Transform boundaries are responsible for shallow earthquakes. E.g. San Andreas fault line

Question 32

Focus 4 Plate Tectonics: Explain Convergent (continent - continent) plate boundaries.

Answer 32

Continental plates moving towards each other When two continents meet head-on, neither plate moves under the other because the continental rocks are relatively light and instead the crust buckles and is pushed upward or sideways.

Question 33

Focus 4 Plate Tectonics: Convergent (continent - continent) plate boundaries & types of tectonic events.

Answer 33

Mountain ranges are formed. E.g. Himalayas

Question 34

Focus 4 Plate Tectonics: Explain Convergent (ocean-ocean) plate boundaries.

Answer 34

Oceanic plates moving towards each other. One of the oceanic plates subducts under the other oceanic plate.

Question 35

Focus 4 Plate Tectonics: Convergent (ocean-ocean) plate boundaries & types of tectonic events.

Answer 35

Deep oceanic trench is formed at the meeting of the two plates. Undersea volcano's formed and erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs. E.g. Mariana Trench and Mariana Islands (near Philippines)

Question 36

Focus 4 Plate Tectonics: Explain Convergent (ocean-continent) plate boundaries.

Answer 36

A continental plate and an oceanic plate moving towards each other. The oceanic plate subducts under the continental plate.

Question 37

Focus 4 Plate Tectonics: Convergent (ocean-continent) plate boundaries & types of tectonic events.

Answer 37

The continental plate lifts up creating mountain ranges (often volcanic mountains). An ocean trench created where the continental boundary meets oceanic plate. E.g. Nazca Plate under South America (which has created the Andes Mountains and the Peru Trench).

Question 38

Focus 5 Explain how seismic waves work.

Answer 38

Waves are disturbances in space that carry energy from one place to another They are produced by a vibrating source Seismic waves are produced by energy released during an earthquake Insert Image of Wave Diagram Amplitude: measures the height of the crest of the wave from the midline Wavelength: refers to the length of a wave from one peak to the next Frequency: refers to the number of waves that pass a given point in a given time period Seismic waves are waves of energy caused by tectonic activity Body waves: Primary (P) and Secondary (S) waves Surface waves: Rayleigh (R) and Love (L) waves

Question 39

Focus 5 Describe body waves: P-waves.

Answer 39

Primary - push and pull waves (longitudinal waves) Can travel through liquid and solid so they can travel through the earth’s core Fastest body wave, averaging approximately 6 km/s Bent by the changing density of the rock – they are bent sharply when the material changes suddenly

Question 40

Focus 5 Describe body waves: S-waves.

Answer 40

Secondary - side to side waves (transverse waves) Can only travel through solids Slower than P-waves, approximately 4 km/s Bent by changing density of rock – bent sharply when material changes suddenly

Question 41

Focus 5 Describe surface waves.

Answer 41

Typically generated when the source of the earthquake is close to the earth’s surface Travel just below the surface of the ground Although they travel more slowly than body waves (P and S waves) they can be much larger in amplitude and are often the most destructive type of seismic waves The two most common varieties are Rayleigh (R) and Love (S) waves