HWSUC - The Ultimate Tree

colonies of photosynthetic cyanobacteria (blue-green algae)

provide some of the oldest evidence of life on Earth-- 3.5 bya (found in western australia)

Vegetation Indicators
-Plant fossils
-Coal Deposits

Climate Indicators
-Oxygen Isotopes in marine fossils
-Bubbles in ice cores
-Chemical Composition of fossils

evolve roughly 120 mya during Cretaceous

major evolutionary innovation

90 mya -- angiosperms dominate ecosystems

65 - 2.5 mya

Major shift from warm and wet "greenhouse earth" to cool, dry "icehouse earth" (formation of polar icecaps)

Characterized by moist closed forests ~ rainforests

55mya australia begins rifting from antarctica.

"The Long Drying" (very important)

35 mya = Final seperation of Australia from Antarctica

Australia drifts north into latitudes characterized by high pressure systems = dry

25-15 mya = transition from ancient rain forests to drier vegetation

15 mya = Australian plate collides with South East Asia = mountains in New Guinea = N. Australia in "rain shadow"

Scelerophyll fossils date back to 50-35 mya = rainforest origins

As conditions dry/soil fertility declines, Sclerophylls emerge.

-Stomata protected in grooves (boundary layers)--limits excessive water loss

Leaf shape/orientation

(1.8 mya - 10 kya) overall cooling trend

-cyclical temperature oscillations (long glacial and relatively short interglacial periods)

-Western civilization = entirely interglacial

*45 kya -- Aboriginal people settle Australia

partial explanation for Ice Ages

3 Cycles
-Obliquity -- tilt of the Earth (cycles every 41 KY)

-Eccentricity - elliptical orbit (cycle of 100 KY)

-Procession - slight wobble in Earth's orbit (cycle ~ 21 KY)

The interaction between these cycles may explain ice age trends

*Forcing factors must also be at work (ex. ocean currents)

Ice Ages in Australia were characterized by hyper-aridity (extreme dryness)

Vegetation responded with expansions and contractions

Glacial -- dry rainforests/sclerophyll

Interglacial - wet rainforests

Last Glacial Period (100 K) -- fire became more significant = Eucalyptus expanding at expense of Casuarina & dry rainforest

Fire-stick farming (from 45 KYA) further encourages Eucalypts

a small area with microclimate allowing an "escape" from climate change. Sensitive vegetation types retreat here for survival.

Usually defined by topography (canyons and valleys) -- moisture accumulates enabling organisms to survive in dry times.