Plant and Earth History

Question 1

What plants initially terrestrialised earth - Ordovician?

Answer 1

• Simple, non-vascular - photosyntehetic leafless plants
• Evolved predominantly from fresh water algae
• This expansion of plants drew down CO2 from 5000 to 2500 ppmv
• Caused glaciation

Question 2

How did plants diversify and disperse in the Silurian period?

Answer 2

• Simple vascular plants, still leafless, photosynthesizing as naked stems
• Late silurian - life began to flourish - forests to appear - leaves became widespread

Question 3

What happened in the Devonian - Carboniferous period?

Answer 3

• Vascular plants
• Dense forests, deeper roots - more drawdown of CO2
• Influenced nature of rivers and floodplains

Question 4

When were leafy plants established?

Answer 4

• Carboniferous period - ~360 Mya

Question 5

What happened in the cretaceous period?

Answer 5

• Flowering plants originated
• Radiation characterized by high and rapid diversification and high rates of speciation
• Angiosperm forests

Question 6

Why did we get angiosperm radiation?

Answer 6

• Break up of Pangea led to expansion of temperate zones - higher temp and rainfall
• Spread of angiosperms facilitated by novel fire regimes
• Insect pollination key contributor to radiation on angiosperm

Question 7

When did C4 plants rise?

Answer 7

• C3 carbon fixation originated early - in Cretaceous
• C4 photosynthesis - tropical grasses in Oligocene - advantageous at higher temps and lower CO2 concs
• Is now thought that addtional water availability was a critical factor in the emergenece of C4 - C4 photosynthesis less water loss than C3

Question 8

How can we tell what the environment conditions were in history?

Answer 8

Macrofossil evidence:
- Fossil wood
- Leaves

Microfossil evidence:
- Pollen grain and spores - gives idea of what plants present - tells us about climate
- Charcoal - tells us about fires - and what vegetation - climate

Question 9

What two approaches can we use to make quantitative estimates of climate from leaves?

Answer 9

Physiognomic approach - based upon aspects of plant architechture constrained by environmental conditions - CLAMP - climate leaf analysis multivariate program - generates climate metrics - use this to evaluate climate models

Nearest living relative (NLR) and the coexistence approach - based on the environmental tolerances of assumed living relatives
- Need NLR, recent distribution of NLR and climate bands

Stomatal density - as pCO2 proxy:
- Can meaure stomatal density and stomatal index - tell us about past CO2