Life and Geological CO2 + O2 Cycles

Question 1

What caused the fluctuations of oxygen and carbon dioxide over time?

Answer 1

5 mass extinctions

Land being colonised by plants and then the expansion of carboniferous forests increased oxygen levels and decreased carbon dioxide

High volcanic activity and low volcanic activity

Question 2

How can plant activity impact weathering?

Answer 2

• Respiration and evapotranspiration increases global rainfall
• More carbon dioxide in rainfall causes an increase in weathering
• Plant roots stabilise soil particles which holds them in place when the rain washes over
• Increases weathering
• Plant roots from associations with mycorrhizal fungi and they both secrete acid into the soil
• Lowers soil pH and increases weathering
• Plants root and mycorrhizal fungi respire underground and release CO2
• This dissolves in the soil to from carbonic acid which lowers soil pH and increases weathering
• Leaf litter and dead plants are decomposed by fungi and microbes in the soil
• This releases CO2 and organic acids which lowers soil pH and increases weathering

Question 3

Do plants speed up or slow down the geological carbon cycle?

Answer 3

Speed up

Question 4

How is deforestation affecting the geological carbon cycle?

Answer 4

Removes the weathering effect of plant roots

Question 5

How is acid mine drainage affecting the carbon cycle?

Answer 5

Mining exposes pyrite to oxygen which produces sulphuric acid

Sulphuric acid then weathers limestone and other carbonate rocks which releases CO2 and HCO3

Question 6

What do burning fossil fuels act as?

Answer 6

Like a fast-acting volcano

Question 7

What are humans doing do the geological cycles and carbon cycles?

Answer 7

Short circuiting the geological cycle

Speeding up the geological carbon cycle

Question 8

When does oxygen decrease?

Answer 8

More CO2 = less O2

When carbon containing organic matter is burned or decomposed it uses oxygen e.g. burning fossil fuels and deforestation

Question 9

What is enhanced rock weathering?

Answer 9

Increase the amount of weathering taking place globally

Physically break up and spread out silicate rocks - gives a higher SA for weathering of silicate rocks

Silicate rock weathering takes up carbon dioxide into the soil

Eventually the carbon ends up in long-term storage in the oceans due to run-off

Question 10

What are the benefits for enhanced rock weathering?

Answer 10

Can use industrial waste from mining silicate rocks

Can be used on agricultural land so no competition for land/land use change

Can fertilise agricultural land as it contains phosphate and potassium