GEOG20009 Lecture Notes - Lecture 21: Great Artesian Basin, Abrupt Climate Change, Central Australia
15 May 2018
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LECTURE 21: GONDWANA TO ANTHROPOCENE
EVOLUTION ON AN ISLAND CONTINENT
• Modern Australian flora had origin in Gondwana – particularly ferns & gymnosperms
• Tectonically stable after 90Ma – highly leached, deep weathering soil profiles cover most of Australia – lost soil
nutrients
• Eucalypts: adapted to environment, over 700 different species (diversification), originally rainforest, now sclerophyll
forest
o Leaves adapted due to long isolation, poor soils & increasing aridity – built hard leaves & coatings to
reduce transpiration, also resistant to fire
o Refugia along streams for water – use groundwater (extensive root system)
• Megafauna (Quaternary): body size larger than 45kg – kangaroo, wombat etc. – Aboriginals v Climate Change as
cause of extinction – Naracoorte, SA (fossil site)
150Ma
First flowering plants & conifer forests in much of Australia
120Ma
Rifting, stretching and transgression of seas - covering land of Australia
100Ma
Dinosaurs, still connected to Antarctica, shallow seas – Great Artesian Basin (mound springs – endemic fish
& plants)
80Ma
Sea floor spreading (96Ma), rifting to drifting, separated from Antarctica – ISOLATION (marsupials reached
Antarctica in Eocene, then found in Australia 35Ma – followed land bridges and vegetation belts)
40Ma
Form own oceanic crust surrounding continental plate, marsupials in Australia
10Ma
Drifting to north, large ocean mass between other continents, change in climate system (Antarctica now ice)
– development of strong wind currents and strengthening of south westerlies – greater temperature
differences between latitudes – DRYING TREND IN AUSTRALIA (rainforest to grassland, organisms evolved to
the climate – adapted or migrated)
LECTURE 22: HUMAN IMPACT
MEGAFAUNA EXTINCTION IN AUSTRALIA
• Exact timing of human arrival uncertain in Australia – accepted as 60,000
• Aboriginals – yet no evidence of markings on bones, maybe their use of fire, no kill sites, no evidence of human
presence in Central Australia until 30,000
o History of humans in other continents killing the megafauna – prehistoric overkill hypothesis
o Human-mediate extinction hypotheses assume no climate change
• Some megafauna extinction coincident with abrupt climate change
• Most climate and landscape reconstructions are based on assumptions
• Clear evidence of major hydro-climatic changes within 50-45,000 extinction window of megafauna in Central
Australia
• Decrease in megafauna species cyclically declining – slower and lesser recoveries over time – long term decreasing
trend
o Extinction Spiral caused by:
▪ Increasing aridity, shrinking rangelands
▪ Low reproduction rates among large species preventing replacement frequency required
▪ Minor anthropogenic hunting & burning
HUMAN IMPACT AND GLOBAL CHANGE
• Growing global population is the main driver of global change – exponential growth
• Increasing need for energy use
o Stage 1: 1800-1945: deforestation and Industrial Evolution
o Stage 2: 1945-2010: Great Acceleration – global networks, politics and societies
o Stage 3: Vulnerability/Climate Change
• Main observation: exponential growth of species extinction
o Currently 6th largest mass extinction
• Human Impacts on Biosphere: cropland, pasture – deforestation
• Anthropogenic transformation of the biomes – irreversible
• Anthromes: new way of looking at biosphere – include humans into the landscape
• Novel Ecosystems: fragmented landscapes
o Implications for habitat sizes, populations, turnover, dispersal and immigration – effect on diversity
o Biodiversity conservation must be extended to habitats directly shaped by humans
Document Summary
Evolution on an island continent: modern australian flora had origin in gondwana particularly ferns & gymnosperms. Tectonically stable after 90ma highly leached, deep weathering soil profiles cover most of australia lost soil nutrients. Eucalypts: adapted to environment, over 700 different species (diversification), originally rainforest, now sclerophyll forest. Aboriginals v climate change as cause of extinction naracoorte, sa (fossil site) First flowering plants & conifer forests in much of australia. Rifting, stretching and transgression of seas - covering land of australia. 100ma dinosaurs, still connected to antarctica, shallow seas great artesian basin (mound springs endemic fish. Sea floor spreading (96ma), rifting to drifting, separated from antarctica isolation (marsupials reached. Antarctica in eocene, then found in australia 35ma followed land bridges and vegetation belts) Form own oceanic crust surrounding continental plate, marsupials in australia. Drifting to north, large ocean mass between other continents, change in climate system (antarctica now ice)
