G3 key idea 2 and 3

Question 1

the Wilson cycle

Answer 1

1. a continent rifts when it breaks up, magma rises, stretching and fracturing the crust
2. rifting progresses and forms a narrow sea between divergent plates, basaltic oceanic crust forms
3. a full ocean basin develops with a mid ocean ridge, continents move further apart
4. subduction zones form as oceanic crust starts to be consumed, ocean basin begins to sink
5. ocean almost completely closed and continents begin to collide
6. continents collide and mountain belts form, ocean completely closed

Question 2

how mountain building/ uplift (orogeny) and sinking changes the composition of the atmosphere

Answer 2

sinking and uplift can be due to tectonic movements, including mountain building

sinking may be a result of human activities such as groundwater removal or mining

uplift means more rock is exposed, increasing the rate of chemical weathering
CO2 from the atmosphere reacts with decomposing rock minerals forming bicarbonates (calcium carbonate)

bicarbonates then transported via rivers and deposited on ocean floors as sediment
leads to global cooling due to decrease of natural greenhouse effect from removing CO2

Question 3

volcanic activity

Answer 3

although particles in atmosphere initially reflect solar radiation (cooling climate)
long-term greenhouse gases would raise temperatures

Question 4

human activity

Answer 4

removing carbon sink - deforestation
burning fossil fuels

added methane to atmosphere through release of methane hydrates as temp increases

Question 5

isostatic

Answer 5

sea level changes are due to uplift or subsidence of the continental crust

often sinks when loaded with ice or sediment
rising again when material is removed

these are only seen in the affected region

Question 6

eustatic

Answer 6

sea level changes are due to changes In the volume of water, seen worldwide

Question 7

the Anthropocene

Answer 7

proposed to initially draw attention to the permanent damage being done to the environment and to life on earth

Question 8

evidence for the Anthropocene

Answer 8

widespread human footprint
transformed ~75% of the earths land surface
plastic pollution is now found in deep sea trenches and arctic ice
estimated that 8.3 billion tonnes of plastic has been produced since 1950

global and rapid environmental change
atmospheric CO2 levels have skyrocketed
causing global average temperatures to rise by 1.2 degrees since 1850

production of concrete
leaves a distinct and durable layer in the earths stratigraphy
fragments of concrete are already appearing in sedimentary layers, landfills and urban geology

Question 9

evidence against the Anthropocene

Answer 9

geological time requires deep time perspective
epochs usually span thousands to millions of years
the proposed Anthropocene (starting at 1950) is too short at just 75 years)

holocene already includes human impact
human influence began much earlier
agriculture started ~10,000 years ago
deforestation and early mining during the bronze and iron ages

critics argue that focusing on the Anthropocene risks oversimplifying the complexity of human impacts

Question 10

evidence for changing climate

Answer 10

coal - rapid plant growth requires high rainfall and high temperatures such as tropical rainforest found in equatorial regions

desert sandstone -desert sands are fine grained, very well sorted and rounded

evaporites - rainfall is low and evaporation is high, e.g. in hot deserts

tillites - ancient boulder clay deposits so are glacial deposits

reef limestone - restricted to latitudes of less than 30 degrees north or south of the equator

Question 11

isotopic evidence

Answer 11

the majority of the worlds oxygen is 16O but a noticeable percentage is 18O

the lighter 16O isotope is removed more easily by evaporation, so tends to leave more 18O behind in the ocean, altering the ratio between the two

under normal circumstances, the 16O in the evaporated water is returned to the ocean after falling as rain or snow

in periods of glaciation, the light oxygen is trapped in the ice caps or glaciers
as temp drops globally, the ratio of 18O to 16O changes

more 18O is present in the oceans in colder temperatures
once ice caps melt and the 18O to 16O ratio has returned to normal, the only evidence of the change remains in the oxygen of the calcium carbonate shells of bivalves and other microfossils

Question 12

evidence for snowball earth

Answer 12

glacial deposits (till and dripstones) that have been found in what were tropical conditions close to the equator

varves - alternating light and dark layers of sediment in glacial lakes, with each pair representing one year
summer deposits will vary in thickness according to the amount of meltwater produced

glacial striations