Carbon Cycle 2

Question 1

What percentage of our Earth’s history was glaciated?

Answer 1

• about 10% of our Earth’s history was glaciated
• most extreme Earth glaciations occured in the pre-Cambrian period (before 540 my)
• two major glaciations occurs in the Cambrian period (Carboniferous glaciation 250 my - 350 my, and Pleistocene glaciation 1.8my)

Question 2

What are the three different kinds of rocks?

Answer 2

1. Igneous rocks
   - formed under high temperature
   - cooling and solidification of magma (rich in calcium silicate)
2. Sedimentary rocks
   - formed with water
   - lithification of fine materials decomposed from Earth’s rocks
3. Metamorphic rocks
   - formed under high pressure

• the 3 rock types can be changed between each other
• SG has igneous rocks at Bukit Timah Hill

Question 3

What are the 2 main kinds of igneous rocks?

Answer 3

Basalt

• Mafic (dark, high density, Mg and Fe, mostly form at oceanic crust)
• Extrusive (cools fast, forms big crystals)

Granite

• Felsic (light coloured, low density, Si and Al, mostly form continental crust)
• Intrusive (cools slowly, forms small crystals)

Question 4

What is the structure of Earth’s layers?

Answer 4

1. Oceanic Crust
   - 3 - 10km thick
   - basaltic rock
   - young (~200 my ago)
   - oldest oceanic crusts are found in subduction zones
2. Continental Crust
   - 35km thick
   - granitic rock
   - old (~4 by ago)
3. Mantle
   - ~3000km thick
   - Mg-Fe silicates

Question 5

What is the lithosphere and athenosphere?

What is the composition of the core?

Answer 5

Lithosphere

• crust and upper mantle
• rigid and brittle

Athenosphere

• mantle
• ductile due to high temperature

Outer-core - liquid
Inner-core - solid

Question 6

What are the 3 types of plate movement?

Answer 6

1. Convergent
   - Subduction zones - dense oceanic crust sinks under less dense continental crust e.g. Mariana Trench
   - High mountains - two continental crusts collide
2. Divergent
   - mid-ocean ridges
3. Transform faults (e.g. California)

Question 7

(Evidence of Plate Movements)

What is Continental Drifting?

Answer 7

1. Continental Drifting
   - Alfred Wegner proved that the Earth had a single super- continent called the Pangaea (300 to 200 m.y. ago)
   - common fossils were found on different continents
   - distribution of glacial features explained best when continents are put together
   - however, Wegner could not explain why continents move

Question 8

(Evidence of Plate Movements)

What is Paleomagnetism?

Answer 8

2. Paleomagnetism
   - Earth has a magnetic field caused by molten fluids moving in Earth’s core
   - when molten lava is cooled beyond ~570°C (Curie Point), volcanic rocks become magnetized in direction of Earth’s magnetic field at time of cooling
   - Radiometric age dating to provide age of rocks (U-Pb, Th-Pb, K-Ar)
   - able to track movements wrt latitude up to 500 m.y. ago

Question 9

(Evidence of Plate Movements)

What is Sea floor spreading?

Answer 9

3. Sea-Floor Spreading
   - proved that movement of plates was caused by seafloor spreading, not continental drifting
   - able to measure seafloor spreading rates by paleomagnetic changes in the oceanic basalts
   - magma erupts and are equally distributed on both sides, and magnetized
   - able to tell sea floor spreading due to reversal of polarity of rocks formed
   - rocks are dated by K-Ar methods

Question 10

(Evidence of Plate Movements)

What is the Wilson Cycle?

Answer 10

Wilson Cycle

• Continents assemble into a super-continent, breaks apart, and forms again
• 1 cycle takes about 500 m.y.
• reasonably constructed up to 500 m.y. ago
• Goodwana was earliest, Pangaea was latest

Question 11

What are lithospheric plate movements caused by?

Answer 11

• Divergent margins (crust being created)
• Convergent margins (crust being destroyed)
• Transform margins (crust slides past each other)
• Mantle convection causes ridge push (mid-ocean ridges) and slab pull (subduction zones)

Question 12

What is the rock cycle?

Answer 12

1. oceanic plates subducted and melted into magma in the athenosphere
2. Subducted sediment erupts from island arc volcano (oceanic-oceanic) and mountain chain volcano (oceanic-continental)
3. erosion of volcanic rock provides complete cycle

Question 13

How fast do plates move?

Where are hotspots located? (volcanos within a plate)

Answer 13

• 4cm/year
• Hawaii
• Yellowstone National Park