Week 2

Question 1

How do we know that the earth is 4.6 billion years

Answer 1

The oldest Rock/ Continental Crust is 4.6 Billion yrs old
Australia and Canada has the oldest overriding tectonic plates and this is also the oldest rock. (Found in canada)
Hence the age of the earth is derived from the age of the oldest rock

Question 2

What is the oldest rocks called

Answer 2

Cratons

Question 3

What are the four major structure

Answer 3

1. Crust (Oceanic -5km and Continental- 30 to 40km)
2. Mantle- 2885km
3. Outer Core- 2270km
4. Inner Core- 1216 km
   each layer has a unique chemical composition, physical state and can impact life on earth’s surface

Question 4

The internal dynamics of the earth

Answer 4

The lithosphere is the solid, outer part of the Earth
The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layer of Earth’s structure
It is bounded by the atmosphere above and the asthenosphere below.

Question 5

What was Alfred Wegener Concept of Continental Drift

Answer 5

He believe that earth’s continents had moved over geologic time relative to each other, thus appearing to have drifted across the ocean bed
- the continents seems to fit together like puzzle pieces
- if you fit them together, you can match fossils of animals and plants across the continental edges
- Glacial striations also match across the continental edges which suggested a common origin point

Question 6

Why were people skeptical of Wegener’s idea of continental drift

Answer 6

• they knew that most of the earth is solid rock
• only the outer core is molten rock
• A slice into the earth shows a solid inner core and a liquid outer core, both composed of nickel and iron
• The earth’s solid mantel makes up most of the volume of the earth
• The earth’s crust on which we live on is as thin as a line at this scale
  HENCE HOW CAN CONTINENTS DRIFT ON A SEA OF SOLID ROCK?
• There was a lack of mechanism for drift

Question 7

Why is plate tectonics a scientific theory

Answer 7

it explains how major landforms are created as a result of Earth’s Lithosphere movements which can explain many phenomena, including mountain building events. volcanoes and Earthquakes

Question 8

How was Wegener’s Idea revived

Answer 8

By Harry Hess
By Bruce Heezen and Marie Tharp

Question 9

What did Harry Hass do

Answer 9

Mapped the ocean floor bathymetry during world war 2, which provided one of the most important evidence to support plate tectonics theory

Question 10

What did Bruce Heezen and Marie Tharp do?

Answer 10

Mapped the Mid-Atlantic ridge and found that the mid ocean ridge was higher

Question 11

Magnetization patterns on sea floor

Answer 11

Ocean crust is striped with parallel bands of magnetized rock with alternating polarities
Stripes are parallel to the mid-ocean ridge and the pattern of the stripes are symmetrical

Question 12

Concept of Geodynamo

Answer 12

The earth contains a liquid iron-nickel outer core
The convection and rotation of this conductive fluid creates the geodynamo which is a self sustaining magnetic field that encompasses the entire Earth. The magnetic field of the earth can flip its polarity

Question 13

The earth’s magnetic field

Answer 13

Inclination - tilt of the compass needle from horizontal. Depends upon
1. Normal or reversed polarity
2. Latitude

Question 14

Process of magnetization

Answer 14

1. When a volcanic rock erupts, it contains particles of magnetic minerals and these minerals would want to align with the Earth’s magnetic field
2. But the magnetic particles can only move when the rock is hot as once it cools down, they are frozen in place
3. It turns out that the earth’s magnetic field periodically reverses
4. When this occurs, we get some rocks with magnetic fields frozen in current orientation and some frozen in reversed orientation

Question 15

Ocean spreading centers

Answer 15

1. Linear boundary between two diverging lithospheric plates on the ocean floor
2. Two plates move apart from each other
3. Molten rock wells up from the underlying mantle into the gap between plates
4. Solidifies into new oceanic crust
5. Found at the crest of oceanic ridges

Question 16

Summary of the Evidences (in addition to Wegener’s evidences )

Answer 16

1. Global Seismicity delineate the plate boundary
2. Deep seismicity indicate the slab (old, heavier plate) has been subducted into the deeper part of the earth
3. The magnetic anomaly across the mid-ocean ridge supporting the spreading of the seafloor
4. The mid-ocean ridges are higher than the nearby seafloor

Question 17

What are the three types of plate boundaries

Answer 17

1. Convergent
2. Divergent
3. Transform

Question 18

What are divergent boundaries

Answer 18

• Where two plates are moving apart
• The space created can be filled with new crustal material sourced from the molten magma that forms below
• Divergent boundaries can form within continents but eventually they will open up and form oceanic basins
• On land they produce rift valleys
  Under the ocean they produce mid oceanic ridges

Question 19

Why are some young oceanic floor wider than other young oceanic floors

Answer 19

The speed that it moves apart from the mid oceanic ridge is faster hence wider

Question 20

Why is oldest ocean floor the deepest

Answer 20

The rocks become cooler, hence they become denser and slowly sink lower and lower into the mantle

Question 21

Driving force in plate tectonics

Answer 21

Convection of the Earth’s solid mantle raises hot rocks beneath mid-ocean ridges. These rocks spread laterally, cool, and sink back into the interior of the mantle, driving plate tectonics

Question 22

Convergent boundaries

Answer 22

• Where two plates are colliding
• Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust
• The denser plate is subducted underneath the less denser plate
• The plate being forced under is eventually melted and destroyed
• Subduction zones are responsible for the largest earthquakes and also form chains of volcanoes in the overriding plate
• Subducting zones can also exist between two oceanic plates and in this case we will get a chain of volcanoes

Question 23

Transform Boundary

Answer 23

• where two plates slide pass each other
• the relative motion of the plates is horizontal
• they can occur underwater or on land
• crust is neither destroyed nor created
• Because of friction, the plates cannot simply glide pass each other
• Rather stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released and results in earthquakes
• Some transform boundaries are associated with oceanic spreading ridges which are irregular and jagged (compsed of segments of spreading ridge connected by segments of transform faults)
• Transform boundaries are on the edges of plates

Question 24

Summary of plate tectonics theory

Answer 24

• the lithosphere is broken into tectonic plates (seven or eight major plates)
• Earthquakes, volcanic activity, mountain-building and oceanic trench formation occur along the plate boundaries
• Tectonic plates are composed of oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust