Changes to geosphere, Atmosphere & Hydrosphere 5.2

Question 1

How the impacts of living things changed the Geosphere?

Changes to geosphere?

Answer 1

the cyanobacteria began releasing C02 from photosynthesis reacting with iron and forming insoluble rust
>Iron oxide precipitated forming thin layers on ocean floor
>this meant photosynthesis couldn’t stay in atmosphere as oxygen kept combining with iron to form sediments on ocean floor
-skeletons of silica caught in oxygen (oxygen poisonous and killed them) formed layer of silica of iron-oxide e.g. WA Alternating layers maybe due to seasonal changes?

Question 2

Banded Iron Formations?

Answer 2

• Alternating layers of iron oxide rich sediments with layers of silicate minerals
• sedimenatry rocks from the Archaean and Proterozoic
• show changes in levels of oxygen in atmosphere & oceans
• make up 60% worlds iron deposits

Question 3

Experiment to simulate BIFs?

Answer 3

1. Two test tubes with iron sulfate.
2. One sealed and one open
   Results:
   Open tube develops brown sediment
   This is insoluble iron oxide

Question 4

How the impacts of living things changed the Atmosphere?

Changes to C02 levels?

Answer 4

• early atmosphere heaps of C02 from outgassing of volcanoes
• When oceans formed (water vapour condensing to liquid>rain for millions of years) the C02 dissolved in water
• calcium & Magnesium dissolved in ocean>reacted with carbonate > formed limestone deposits & chalk rocks
• this all massively reduced C02 as locked up in crust rocks

Question 5

Precipitation of Carbonates Prac Work

Answer 5

1. Blow C02 into limewater through straw

2. solution goes cloudy and solid calcium carbonate precipitates on bottom and a solid sediment

Question 6

Major Carbon Sinks (5 of them)?

Answer 6

1. Biomass
   - mass of living flesh & tissue
   - Plant biomass ( starch, proteins, fats) dies/ decays and heaps of C02 is locked away in living things and dead things in soils/sediments/swamps
2. Fossil Fuels
   - Some dead biomass decays & recycles into coal and petroleum
3. Calcareous Skeletons & Shells
   - Skeletons & shells formed from calcium carbonate from dissolved C01
   - shell material doesn’t decompose after this> adds to limestone deposits
4. Limestone Deposits
   - C02 dissolved & reacts with dissolved minerals to form carbonate sediments (limestone deposits)
5. The Oceans
   - contain way more dissolved C02 then in atmosphere

Question 7

Oxygen and Ozone was essential…

Answer 7

requirement for life on land was formation of ozone layer

Question 8

Chemical relationship of Oxygen(O2) & Ozone(O3)?

Answer 8

-Both molecules from oxygen atoms but different chemical properties
-Ozone chemically dangerous
-Ozone blocks UV > UV kills cells & destroys DNA:
no ozone = no life
-oceans naturally UV resistant

Question 9

How Ozone is formed?

Answer 9

Estimated that during Cambrian explosion a UV blocking ozone layer formed to help animals get from oceans to land

Question 10

How the impacts of living things changed the Hydrosphere?

C02 and Methane

Answer 10

• trap heat from sun & prevent re-radiation of heat back to space > warming
• water vapour causes largest part of greenhouse effect

Question 11

Water Vapour & Temperature?

Answer 11

• Hotter it is > more evaporation

- Global temps increase > more warming & rain

Question 12

Evidence for Hydrosphere changes in the Past?

Answer 12

-Mawson identified thick & widespread glacial deposits in SA 150 ya & concluded with possibility of a huge “ice age” in distant past
> similar deposits found in Scotland & Norway (all pre Cambrian)
-1992 > proposal of snowball earth/ complete world freeze

Question 13

Snowball Earth?

Answer 13

• radiometric dating shows global glaciation dating to 2.4 bya (Huronian)
• another one to 750 mya (Cryogenian)

Question 14

Huronian Snowball Earth…

Triggered by…

Answer 14

-glaciation as result of “great oxygenation effect”
> Cyanobacteria furiously photosynthesising in stromatolites (produce heaps of oxygen)

Triggered by:

• Oxidation of Methane
• methane 20 times potent as a greenhouse gas than C02 back then
• methane destroyed by oxygen > so photosynthesis removed methane from atmosphere > SNOWBALL EARTH
• Continents & Tectonics
• 2.5bya volcanic activity was low > small amounts of C02 being produced > SNOWBALL EARTH
• Albedo Feedback Cycle
• once reduced greenhouse gas leads to glaciation > albedo increased from reflective surfaces causing further cooling from suns radiation to space
• climate modelling shows feedback is potent in tropical areas as solar radiation is maximum so once feedback cycle commences > SNOWBALL EARTH is inevitable

Question 15

*Tectonics Break Ice-Lock

Answer 15

-Snowball earth melted by tectonic rifting > volcanic activity > release of C02 finally