preliminary biology mod 4

MOD

TOPIC

4

POPULATION DYNAMICS

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Scientists are able to apply their knowledge of population dynamics to unexplained extinctions.

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The type and number of species on the planet are constantly changing.

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During the Pleistocene Epoch there were a number of megafaunas in Australia.

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Extinction of megafauna is thought to have been due to human impact along with climate change.

THEORY 1: CLIMATE CHANGE

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Continent dried out

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Rainforests were contracting – stored moisture and returned moisture to the atmosphere.

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Eucalypt forests replaced these, and water was not as efficiently retained.

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Became hotter and drier, fires broke out due to lightning.

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Plants and animals that survived the drought and fire reproduced  changing the flora and fauna.

THEORY 2: ARRIVAL OF HUMANS

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Aboriginal people arrived  successful predators.

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Used ‘fire stick’ farming techniques.

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Introduction of dingoes may have reduced the diversity of carnivore predators.

THEORY 3: LEVEL OF NUTRIENTS

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Low level of nutrients in the soil  dry

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Led to smaller animals  can be sustained on less

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Evidence for this can be seen in the smaller size of mammals in Australia compared to counterparts across the world.

EVIDENCE OF HUMAN AND MEGAFAUNA CO-EXISTING

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Cuddie Springs – fossil site in Central NSW  discovery of bones and tools made by humans.

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Kangaroo Leg Bone

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Stone Tools

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Mixtures of megafauna bones

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Charcoal from camp fires

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Sandstone grinding stone

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Additional evidence found at a site north of Melbourne.

PAST ECOSYSTEMS

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It is unclear when humans first became interested in fossils.

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Philosophers hinted that fossils were evidence of previous life.

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Law of superposition  oldest layer at bottom and newest at top.

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Law of original horizontality  all sedimentary strata are originally horizontal

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Law of lateral continuity

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Law of cross-cutting relationships

SLOW CHANGES:

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Changes in the Earth’s crust happened because of slow, progressive causes such as long cycles of erosion and deposition.

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Known as gradualism.

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First geological time scale constructed in 1841.

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Discovery of radioactivity in 1896 by Henri Becquerel led to absolute dating technique to age rocks – age of earth estimated 4.5 billion years.

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Geology and palaeontology are valuable in combination to produce evidence of the past.

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Evidence used to reconstruct past ecosystems is referred to as proxy data.

ABORIGINAL ROCK PAINTINGS

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Represents the longest unbroken art tradition in the world.

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Humans are driven by nature to record details of their existence.

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West Kimberley rock paintings

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Wandjina paintings – 50,000 – 60,000 years old – provide clues about the past.

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Studied scientifically from 2007.

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Radiometric dating is used to date the paintings.

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Uranium/thorium dating can be applied to underlying calcite formations to show when they were formed.

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Evidence of a symbiotic relationship between fungi and bacteria that colonised pigment.

THE GREAT OXYGENATION EVENT

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Approx. 2 billion years ago.

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There was probably limited aerobic respiration prior to this.

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Increased oxygen in the atmosphere had 2 effects

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It created a selection pressure for organisms that could overcome the harmful effects of oxygen.

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Some oxygen metabolites (hydrogen peroxide and hydroxide radicals) are toxic and only organisms with specific new metabolic pathways could take advantage of the benefits of oxygen without it being toxic. These pathways were selected for and allowed the rise of aerobic respiration, leading to development of larger more complex organisms

PALAEONTOLOGICAL EVIDENCE – FOSSILS

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‘Fossil’ from the Latin word fossus - ‘to be mined, dug up, buried or quarried’.

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Fossils are remains of living things or evidence of their past existence.

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They provide clues linking changes in selection pressure to evolution.

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They need to be distinguished from naturally occurring patterns in rocks

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Fossils are generally found in sedimentary rocks due to the way the rocks are formed, preserving evidence from the past

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Classifying fossils

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Mineralised remains (moulds and casts, petrified wood, opalized remains)

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Organic remains (in ice, amber, bogs and dry caves)

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Impressions (shape of external organism recorded in sediment)

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Trace fossils (remnants of organic molecules associated only with life). ‘Geochemical remains’

MICROFOSSILS

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Discovery of Precambrian fossils from Marble Bar, WA (3400-3500 million years old) in silica-rich apex chert (microcrystalline quartz) provided first evidence of past ecosystems on Earth

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Microfossils of single-celled, filamentous anaerobic prokaryotes found, closely resembling modern examples living in hydrothermal vents and volcanic hot springs.

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Infers that these organisms lived in hydrothermal environment

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They are anaerobic and sulfur-metabolising (chemosynthetic) microorganisms

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Scientists infer that chemosynthesis was earliest way for organisms to build organic molecules

CHEMOSYNTHESIS

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Organisms use inorganic compounds available from the environment to manufacture organic compounds

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Does not require sunlight

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Can happen in deep oceans

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Absence of light is a selection pressure

STROMATOLITIC FOSSILS

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Unusually shaped fossils found in Archaean chert at Bitter Springs, NT.

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Dated to around 3.5 billion years old

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Provide valuable information about structure of early organisms and their environment

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In water, colonies of photosynthetic cyanobacteria trap layers of calcium carbonate and ‘grow’ upwards in columns towards the sun.

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Living stromatolites can be found in WA at Hamelin pool, Shark Bay, growing by 1mm per year, individual domes reaching diameter of 200cm and height of 50cm.

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Many selection pressures affected the evolution of stromatolites.

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Modern stromatolites are found in sheltered bays - unique combination of abiotic conditions

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Shallow waters - increased light intensity for photosynthesis, warm still waters allowing growth without disturbance.

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Water is mineral rich and hypersaline (high salinity).