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Environments Through Time
1. evidence from early earth indicates the first life forms survived in changing habitats during the
Achaean and Proterozoic eons

Identify that geological time is divided into eons on the basis of fossil evidence of different life
forms.
The geological time scale is divided into 4 eons: Hadean, Archaean, Proterozoic and Phanerozoic. They are
divided on the basis of fossil evidence of different life forms.
Hadean: (4.5-4 b.y.a) no rocks have survived from this period. NO LIFE
Archaean: (4-2.5 b.y.a) granitoids; greenstones; basalts and pillow rocks (only formed in the oceans therefore
oceans must have existed). All the rocks were highly metamorphosed. Cores of continents formed during this eon.
Very ancient life forms (trace fossils only)
Proterozoic: (2.5 b.y.a-545 ma) plate tectonic super cycle established. Sedimentary rocks deposited on crust
(sandstone, conglomerate, mudstone, limestone). Fossil bacteria and algae
Phanerozoic: (545 ma –present) Complex fossils with hard parts appear. Lots of material is added to continents at
subduction zones
 Outline stable isotope evidence for the first presence of life in 3.8 x 109 year old rocks
Simple Unicellular life forms were present in the Achaean eon in the oceans which were probably established by
this time.
The earliest evidence of life is found in metamorphosed sedimentary rock 3.8 b.y.o found in ISUA, WEST
GREENLAND. The graphite minerals enriched in Carbon 12 in these rocks provides a “signature” of life. There is a
high Carbon 12: Carbon 13 ratio

Outline the processes and environmental conditions involved in the deposition of Banded Iron
Formations (BIF)
Definition: Banded Iron Formations are sedimentary deposits of banded ironstones that are composed of
alternating layers of chemically precipitated iron oxide-rich chert and iron oxide-poor chert.
-Most BIF’s were deposited 2-2.5 byo
How do they form?
Several models are proposed but they all have 2 main features
1. Photosynthetic cyanobacteria produced oxygen and oxygenated the upper layers of the ocean. This
oxygen caused precipitation of soluble iron into iron oxide
2. 2 early Proterozoic oceans contained vast amounts of dissolved iron. Deep water rich in the dissolved iron
(from volcanic activity) was brought up to the surface near continental shelves by upwelling causing it to be
oxygenated
The bands are created by cycles in the precipitation. When all the iron had been precipitated out, iron deposition
stopped and a layer of regular silica rich sediment was deposited.
It took 500 MA took precipitate all the iron in the ocean. The oxygen from the cyanobacteria began to build up in
the atmosphere. Land minerals were then oxidized to form red beds. Cyanobacterial photosynthesis made it
possible to oxygen breathers to evolve. Pyrite disappeared from sedimentary rocks as it is easily weathered by
oxygen and rust. This occurred during red bed formation and the oxygen levels in the atmosphere increased.
These 2 events (red bed formation and removal of pyrite from rocks) was significant as they occurred due to the
production of an oxic atmosphere.
Discuss the significance of BIF’s as evidence of life in primitive oceans.
BIFs provide evidence of primitive life in the oceans by the presence of oxygen that must have been caused by
photosynthesis by life forms.
Define cyanobacteria as simple photosynthetic organisms and examine the fossil evidence of
cyanobacteria in Australia
-Cyanobacteria are simple photosynthetic organisms.
-Stromatelites found in Marble Bar W.A in the Pilbura Region are the
oldest fossil evidence for the presence of cyanobacteria 3.5 BYA
-a stromatelite is a rocky layered deposit formed by communities of
photosynthetic and anaerobic bacteria
-found in chert rocks which is fine grain quartz-containing sedimentary
rock
-dating down by the zircon grains above and below them
-provide EVIDENCE for an inland sea as they can only form in water
(used as a means of protection from harsh sun when there was no
ozone layer)
-we infer that cyanobacteria were present in ancient stromatelites
-These cyanobacteria would have contained chlorophyll-like materials
for photosynthesis
Modern Stromatelites
-rare
-form domes, mats, columns or cones
-discovered in Shark Bay 1960
they require:
-shelter from predators
-warm water
-hyper saline shallow water
-low amounts of tidal flushing
What are the environmental conditions that are required for stromatelite formation? Why has their range
and abundance declined throughout the last 3 billion years?
 Ancient cyanobacteria were able to survive extremely hostile conditions 3 billion years ago.
 They required an anoxic atmosphere and protection from harmful U.V light by a few metres of sea water.
 Modern stromatelites require warm; shallow; hypersaline water, shelter from predators and low amounts of
tidal flushing.
 The abundance of stromatelites has declined over the last 3 billion years
 introduction of an oxic atmosphere caused the abundance of cyanobacteria to decline as oxygen kills of the
cyanobacteria .
 The regression of the global sea levels has declined the range and distribution of stromatelites. Without the
protective covering of shallow sea water there has been significant loss of habitat for the stromatelites This
is evident at Marble Bar in Western Australia where fossil stromatelites suggest that an inland sea once
covered this region.
 The introduction of an oxic atmosphere and ozone layer meant other more complex life forms were able to
evolve. These life forms may have become predators to the stromatelites
Examine and explain processes involved in fossil formation and the range of fossil types
Fossils are the preserved remains or impressions of prehistoric life forms or evidence for their existence
Conditions required for fossil formation: (BSCA)
1. Burial (rapid)
2. Sediment (continual supply of sediment to avoid erosion)
3. Compaction (of sediment)
4. Anoxic conditions
Fossil formation is unlikely for a number of reasons
1) most living things are not fossilized as they are eaten by scavengers or broken down by microbes
2) conditions for fossilization are not present (i.e. rapid burial, continual supply of sediment to avoid erosion,
compaction of sediment into rock called lithification, anoxic conditions, violent storms help produce large amounts
of sediment kilometers thick which bury the organism)
Underwater landslides may preserve entire ecosystems
There are 4 different kinds of fossils
1) Unaltered soft parts: when bacteria and mould are prevented from acting of soft tissue
E.g. Mammoths under ice in Siberia, Animals trapped in tar pits
2) Unaltered Hard parts: Shells of mollusks in young sedimentary rock and hard parts of insects in tree resin/sap
3) Altered hard parts: when the fossils undergo physical and chemical changes i.e by water passing through the
sediment.
E.g. hard parts replaced with silica, pyrite or iron oxide (skeletons), carbonization when fossil turns to black carbon
(often plant matter) and petrifaction when pores of the organism fill with silica from groundwater
4) Trace fossils: The fossils leave a mould which is filled in by minerals creating a cast.
e.g. imprints of soft bodied organisms, burrows of worms, fossil feces(coprolites)
MOULD=the shape/imprint of the organism
CAST= the imprint filled in with new minerals
1.
2. The environment of the Phanerozoic
Oxygen levels through time
There is some evidence we can use to suggest the amounts of oxygen present in the atmosphere including:
-appearance of Red Beds 2 ba (this shows that oxygen levels in the atmosphere must have increased to at least
1% of that of today’s levels)
-appearance of living things in the oceans 3.8 ba
-disappearance of BIFs 2 ba
-The Cambrian explosion (500-600 ma) as invertebrates required 10% of the current oxygen levels
There was practically no oxygen present until 2 bya and since then oxygen levels have been increasing.
Oxygenation of the atmosphere meant the development of ozone layer, decreased CO2 levels due to
photosynthesis and caused global cooling.
Outline the chemical relationship between ozone and oxygen
-Ozone is formed in the stratosphere (upper atmosphere) by photochemical reactions (photo dissociation)
Explain the relationship between the changes in oxygen concentrations and the development of the ozone
layer
The presence of oxygen in the atmosphere:
-increased ozone production and therefore reduced UV radiation that reached earth
-decreased CO2 levels due to photosynthesis by plants
-increased oxygen lead to global cooling (previously the Archaean was very warm as it had high CO2 levels)
Describe the role of ozone in filtering UV radiation and the importance of this for life that developed
during the Phanerozoic eon.
the introduction of ozone layer meant that life could evolve beyond the deep areas of the ocean
ozone is able to filter and prevent most of the dangerous UV radiation from reaching earth
This is important as UV radiation is very damaging. Terrestrial organisms need ozone inorder to prevent
cellular death by disrupting DNA, mutations (cancer), cataracts (in eyes), sunburn, and death of some organisms
i.e. phytoplankton
Identify the major era subdivisions used to describe the general differences in life forms in each era: The
Phanerozoic Eon
Eon
Era
Life Forms
Cenozoic (144 ma-present)
-mega fauna extinction
Phanerozoic
-mammals, birds and flowering plants dominate
-homo sapiens
Mesozoic 248-144 ma
Paleozoic 540-248 ma
-flowering plants
-land organisms dominate
-reptiles and dinosaurs
-first jawed fish
- vertebrates
-amphibians
-land plants
Late Proterozoic and Early Phanerozoic life
During the Proterozoic Eon life changed in many ways:
 Eukaryotes evolved due to ‘endosymbiosis’ (origins of a cells organelles)Cell nuclei developed and primitive
bacteria inserted themselves into cells
 Multicellular plants with discrete organs (tissue specialization)
 Multicellular animals with discrete organs i.e. the Ediacaran Metazoans
Ediacaran Metazoans (620-545 ma)
 Discovered by Reginald Sprigg in 1946 in the Ediacaran Hills, Flinders Ranges
 Found globally in Pound Quartz rock 570 million years old
 Soft bodied invertebrates
 Multicellular
 Specialized tissues and distinct organs
 Range from 1cm 1m
 Possibly burrowing sediment feeders
 4 groups: jelly fish, soft corals, worms, problematica
 2 species include Dicksonia costata and Spriggina
3. The Cambrian Event
The Cambrian explosion/event was the almost immediate radiation of shelled organisms during the early
Cambrian
The Cambrian Period marks the boundary between the Proterozoic and Phanerozoic eons and the almost
instantaneous appearance of large and small shelly animal fossils which are ancestors of present day life e.g.
the Pikara Graciens
At this boundary there is a distinct transition between soft-bodied organisms to hard shelled creatures
The Trichophycus pedum is a trace fossil of a worm burrow and marks the beginning of the Cambrian
Also found abundantly in rocks are tiny cones of calcite called sclerites which were used like armor to
protect organisms. Later on in the Cambrian they are larger and varied in shape and are called small shelly
fauna. These are important as they represent a size and complexity increase as we progress further along the
time scale
50 ma after the Cambrian boundary there is an increase in complexity of fossils
4 possible events that caused the Cambrian explosion
1. Increased oxygen supply allowed larger organisms to survive
2. Predation allowed organisms to obtain more nutritious food supply
3. Genetic mutations increased the rate of evolution
4. Evolution of gills and lungs that are specialized for extracting oxygen in water
The 2 most likely explanations for the Cambrian Explosion
1. increase in oxygen supply:
-animals that use diffusion to obtain oxygen cannot survive in low oxygen environments i.e. metazoans
- increased oxygen supply meant larger more complex animals could evolve
-the presence of larger metazoans supports the idea that there was increased oxygen
2. Predation and hunting:
-due to natural selection animals developed skeletons as it provided more protection
-defense mechanisms were able to arise in response to predation i.e poison secretion, camouflage
-animals that could catch prey had a more nutritious diet
Burgess Shale – black shale
-In Canada
-these rocks contain fossils of almost every sea organism from the Cambrian Explosion
-it is possible that large landslides buried these organisms creating a “frozen ecosystem”
-the Burgess Shale shows that soft-bodied organisms can only be preserved under special circumstances
-fossilized animals found include trilobites, arthropods, mollusks, echinoderms
-The burgess shale is a great example of the incompleteness of the fossil record as soft-bodied fossils are
outnumbered by hard organisms as they cannot preserve as well
-65 000 marine specimens
What does it suggest about ancient life?
-much more diverse
-some are ancestors to modern day fauna
-shows the radiation of life after extinctions
 Distinguish between relative and absolute dating
We do not date fossil but the rocks they are found in
Relative dating determines the order in which things occurred
Absolute dating determines the age of specimens

Compare uses of relative and absolute dating methods in determining sequences in the
evolution of life forms
Relative dating refers to determining rock/fossil age in reference to other rock layers and the geological time scale.
It does not classify a fossils age in terms of years.
Absolute dating: determining the exact age of a rock/fossil in years
Radioisotope datingis based on the decay of radio isotopes found in the rocks to determine the fossil/rocks age
in terms of years. Half lives are used to determine the age of breakdown from when the parent rock first formed.
Fission track dating tracks are found in zircon crystals as a result of radiation. When these crystals are viewed
under an electron microscope we can estimate their age and thus the age of the rock in which the crystals were
found
 Interpret the relative age of a fossil from a stratigraphic sequence
Layers of rocks are strategically sequenced therefore the oldest layer will be at the bottom and the youngest at the
top layer. We can estimate the relative age of a fossil by what layer it found in.

Discuss the possible importance of the development of hardened body parts in explaining the
apparent explosion of life in the Cambrian Period
There are 2 main points why hardened body parts explain the Cambrian explosion:
1. Hard parts provided support for muscle joints and internal organs in organisms and offered protection from
predators and harmful UV rays allowing these organisms to better survive and move onto life where food
availability was higher
2. Hard parts are easily fossilized unlike soft parts leading to an increase in fossils with hard parts found so a
sudden explosion of life seems to occur during the Cambrian Period.

Deduce possible advantages that hard shells and armoring would have given these life-forms in
comparison with the soft bodied Ediacara metazoans of the late Proterozoic, in terms of
predation, protection and defense
Hard parts provided animals with
-protection from predators
-a skeleton to provide a framework to support feeding organs of filter feeders and suspension feeders
-skeletons allow organisms to grow larger and therefore more protection from predators
-skeletons also provide firm points for muscle attachment to improve mobility
-protection from UV
-stops organisms in intertidal zones from drying out during low tides
The Cambrian animals had an advantage over the Ediacara Metazoans as they had hard parts and were all
mobile which allowed them to escape from their predators and move to areas where more food was available.
 Examine the changes in life forms that occurred during what is commonly referred to as the
Cambrian event
Feature
Trilobite (Cambrian explosion)
Ediacaran Fauna (extinct)
Time in which it lived
Cambrian
610 m.a until Cambrian extinction
Mouth
yes
Yes for filtering
Legs
“freely articulating limbs” or yes
No
Eyes
Compound eyes
No
Ability to move
yes
Some were fixed while others were free
movings
Gills
yes
No
Hard parts
Yes
No
Size
larger
smaller
4. Exploiting New Environments
 Outline the theory of evolution by natural selection
Organisms that are best suited to the environmental conditions will survive. These organisms will multiply
producing offspring with their favorable characteristics/genes. They will dominate the population and the others will
die out.
 Outline evidence that present-day organisms have developed from different organisms in the
distant past
-
the fossil record shows the gradual progression of simple life forms into more complex organisms
The evolution of the horse suggests present day organisms have evolved. This is apparent as the
horse has evolved from a dog-sized with 5 toes to the modern day larger size with a hoof. The
developments of a hoof allowed the horse to move quicker and therefore out run its prey and
predators.

Summaries the main evolutionary changes resulting from the selection of living things
exhibiting features that allowed them to survive in terrestrial environments
 Identify the advantages the terrestrial environment offered the first land plants and animals
Advantages
Disadvantages
-more abundant O2
-direct exposure to air=drying out therefore animals
developed scaly skin
-more light for photosynthesis
-new mode of fertilization needed which lead to the
development of internal fertilization and hard-shelled
eggs for protection
-more available habitats
-lung development needed
-less competition for food
-gravity force is greater on land and therefore skeletons
(fauna) and lignin (plants) were developed to hold
against gravity

Outline the major steps in the expansion to the terrestrial environments by land plants,
amphibians and reptiles
All life was marine based until the Ordovician. Early plants colonized near shore environments which encouraged
animals to move closer to the food supply
Land plants: First Vascular Land Plants (Phynophytes):
-primitive group of plants
Features
-reproduction via sporangia
-waxy cuticles to prevent drying out
-stomates which are pores for gas exchange
-xylem tubes for water movement up/down the plant
Evolution trends
-larger due to lignin
-more complex modes of reproduction
-gymnosperms (cone bearing) and Angiosperms (flowering)
First Land Invertebrates:
-Arthropods (jointed-legs) came first. They were all herbivores
-primitive spiders and scorpions predated other animals. Gills were modified into lungs or spiracles
-Insects during Carboniferous including giant dragonflies. The increase in oxygen allowed animals to grow larger
First land Vertebrates:
-Rhipidistriams probably chased their prey into shallow water where they were able to use their fins to reach their
prey and consume it. It was able to obtain air by nostrils and a sack at the back of the throat
5. Past extinction and mass extinction events
Extinction: when species die out. They occur due to competition between species for the same place in an
ecosystem (niche) or by natural environmental changes.
Radiation: when the survivors of the extinction radiate and flourish replacing the lost organisms
Ecological Niche: the place of a plant or an animal within its ecosystem or community
Distinguish between mass extinctions and smaller extinctions
Megafauna (small)
occur when a large number of
species unique to a specific
geographical area become extinct
i.e. by transgression of regression.
One example is the Tasmanian
tiger.
Mass Extinctions
occur when 30% or more of
kingdom and phyla disappear in a
number of environments world wide
over a geologically brief period (less
than 2 Ma)
When
Theories
60 000-30 000 years ago
There have been 5 major extinctions
known as the “big 5”:
1. Late Cretaceous (60%
species)
2. Late Triassic (75%)
3. Late Devonian (80%)
4. Late Ordovician (85%)
Late Permian (95%)
1. Climate change as Australia
drifted north and became
more arid. Change in
ecosystems from rainforest
to grassland. Reduced water
availability
2. Human intervention as
aboriginals arrived and over
hunted the megafauna. The
megafauna were too big and
slow to run away and
possibly had no fear of
humans. Also fire practices
changed the environment
Assess a variety of hypotheses proposed for the mass extinctions at the end of the Permian and at the
end of the Cretaceous
Permian
KT
When
245 ma
65ma
How and why
-Tectonic plates converged leading
1) -bolide impact: suggests that
to regression and transgression of
an extraterrestrial
sea levels
meteor/asteroid collided with
-Volcanic eruptions lead to global
Earth causing global
warming and anoxic ocean as
wildfires, vaporization of
decaying organism sucked out
ocean, dust in the
oxygen
atmosphere preventing
photosynthesis and global
cooling
2) series of volcanic eruptions
sped up climate change
How many
95% all organisms
60%
Who
mainly marine and fixed bottom
Marine and terrestrial organisms
feeders
Radiation
-dinosaurs
-mammals
-mobile creatures
-some mammals moved into water
-vertebrates
i.e. dolphins and whales
-birds and primates
-angiosperms
Evidence for Bolide Impact:
-impact crater (chixulub crater) in the Gulf of Mexico (Yuctan Peninsula) with a 10km diameter dated at 65 Ma
-Iridium levels in clay are high at the KT boundary rock layer. Iridium is a rare element produced by volcanoes
and typically found in meteors/asteroids
-Unusual deposits at the KT boundary and near the crater from tsunamis, impact debris “tektites” (glassy rocks
melted on impact also known as “shocked quartz”) and fullerenes in clay caused by very high temperature
combustion from global wildfires.
The Bolide impact is the most commonly accepted hypothesis and has more evidence to support this theory than
geological processes and is therefore a more plausible hypothesis.

Compare models of explosive and gradual adaptations and radiation of new genera and species
following mass extinction events
Radiation: occurs after extinctions when the remaining groups of organisms undergo rapid evolutionary expansion
to replace the lost organisms. The new genera or species that radiates have similar features to their ancestors but
are specifically adapted to their environment. After this, rates of evolution slow dramatically due to increased
competition for food/shelter and predators therefore only new genera or species evolve opposed to phyla and
classes.
The geological timescale indicates that there is a constant cycle of extinction and radiation.
The fossil record indicates that evolution has occurred gradually and quickly (in geological terms)
Gradual: Darwin’s theory of evolution believed that evolution occurs through continual changes in organisms over
a long period of time
Explosive: punctuated equilibrium theory proposed by Eldridge and Gould suggests that evolution occurs by rapid
bursts of change within an organism followed by long periods of stability

Discuss two different hypotheses used to explain the extinction of the Pleistocene megafauna
and
 Explain the recent extinction of the marsupial, bird and reptile mega fauna in Australia, as an
example of smaller extinction events involving several large species.
-Not all extinctions are caused by natural factors and often humans are responsible for altering a particular
environment which in turn affects the organisms inhabiting this region.
-The Pleistocene megafauna extinction is considered a small extinction as it occurred in one particular
geographical area and a significant number of marsupials survived.
-there are 2 theories to explain the extinction:
1. Climate change
-occurred 18 000-22 000 years ago
-Australia’s climate became more arid as it drifted northward- changed from cold and dry to warm and dry
-ecosystems changed from forest to grassland and surface water became a scarce commodity
-many organisms lost their habitats and these pressures were too extreme to adapt quickly enough
-it is believed that this may not be a major cause as megafauna had survived previous ice ages before the
Pleistocene extinction
2. Human intervention “Blitzkrieg theory”
-mega fauna’s large size made them slow making them vulnerable to human predation
-human arrival coincides with the beginning of the extinction
-evidence of human ‘butchering’ preserved in megafauna bones
-butchering tools also found hair and residue found from giant kangaroos
-humans also induced vegetation changes Aboriginal back burning
-unable to adapt to the introduction of human predation