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Geological time scale of earth Covers the events that have occurred on earth from its formation to the present time Constructed using the order of rocks laid down in a sedimentary rock sequence Eons are subdivided into eras, subdivided into periods, and subdivided into epochs
First appearance of life Archaeon eon (4000-2500 mya) No oxygen gas on Earth Life first appeared Oldest fossils are microfossils of bacteria
Rise of multicellular organisms Proterozoic eon (2500-541 mya). The earliest eukaryotes, resembling single-celled green algae are known from fossils. Multicellular algae (red and green algae) and the first animals evolved towards the end of this eon
Animals on land Silurian Period (443.8-419.2 mya). The earliest evidence of life on land is from terrestrial rocks of the Silurian period. The first known air- breathing animals were arthropods
First mammals Triassic period (252.1-201.3 mya). Mammal like therapsids are thought to have given rise to the true mammals in the Late Triassic period
First flowering plants Cretaceous period (145.0-66.0 mya). Terrestrial environments were dominated by ferns, seed ferns, cycads and conifers, but angiosperms (flowering plants) also became part of the flora at this time
Fossils preserved remains, impressions or traces of organisms found in rocks of different ages
Fossilisation preservation of hardened remains or traces of organisms in rocks. The chances of an organism becoming fossilized after death are small. Fossilisation occurs when an organism is buried in sediment
Features that assist fossilisation • rapidly covered by sediment. • hidden from scavengers • decreased rate of decomposition • hard tough exoskeleton • protection from weather (wind/sunlight water) • constant humidity • constant temperature
Fossil record implications Land organisms are less likely to be preserved compared to those that are aquatic Delicate plant parts such as flowers are rarely fossilised Fossil record is biased towards certain sorts and parts of organisms and certain environmental conditions
Impression fossil Organism trapped in a rock dissolves away leaving an imprint or mould behind
Cast fossil If the vacant space of an impression fossil is filled with a foreign material
Mineralised fossils occurs when minerals replaces the spaces in structures of organisms such as bones. Minerals may eventually replace the entire organism, leaving a replica of the original fossil (e.g. petrified wood). Process is known as mineralization or petrification
Mummified organisms organisms trapped in a substance under conditions that reduce decay and are preserved with little change i.e. wooly mammoths due to preservation in the frozen ground, insects in amber
Trace fossils sign of an organism such as footprints, teeth or claw marks, nests and eggs, tools, fossilised faeces (coprolites)
Fossilisation process part 1 1. Death of the organism 2. Decay of soft tissue and burial in sediment 3. Sediment accumulation over time 4. Weight of layers squeezes out water between particles of sand, silt or mud
Fossilisation process part 2 5. As the deposit deepens the temperature increases causing solidification of sediments to rock 6. Uplift, erosion and exposure leads to discovery
Relative Dating Relative dating is based on stratigraphy
Stratigraphy the study of the relative positions of the rock strata or layers. Stratigraphy determines age of fossils based on the assumption that lower strata are older and upper strata are younger.
Index fossil fossil of known age found in a particular type of sedimentary rock layer. They are commonly found fossils from similar sites for which an absolute age has been determined
Index fossils should • be distinctive and easily recognisable • be abundant • have lived a short range through time • lived in a wide geographic distribution
Absolute Dating determining the age of a rock directly using radiometric techniques (isotopes). It provides a more precise estimate of age.
Radiometric dating Measurement of the relative abundance of radioactive substances in fossils and rocks in order to determine age Radioactive elements decay into different forms at rates that are constant for a particular element Act as accurate clocks
Radiocarbon dating radiometric dating using an isotope of carbon, 14C. Fossil that contain carbon can be analysed using this technique based on the isotopes half-life 14C decays to nitrogen-14 (14N) and has a half life of of 5730 +- 40 years
Half-life time taken for half of the atoms in a sample to decay from the time that the isotope was incorporated into the organism when it was alive
Potassium-argon dating Potassium-40 has a half life of 1 300 000 000 years until it turns to argon-40
electron-spin resonance Used to estimate the time since material under investigation was last heated, such as when a flint instrument was burnt in a fire or when a tooth last lay exposed on the ground in sunlight Useful for ages of about 50 000 years old to 500 000 years old
Thermoluminescence emission of light from a mineral when it is heated. The amount of light is proportional to the amount of radiation an object has absorbed- the older the object the more light it emits
Biogeography Biogeography is the study of the distribution of organisms and is another type of evidence for the theory of evolution Alfred Russell Wallace recognised from observations that the world may be divided up into a number of biogeographic regions.
Baobab trees Occur in Africa, Madagascar and Northern Western Australia. The distribution of Baobabs suggests that Australia and some of its living organisms are related to Africa Madagascar and their living organisms despite being across the Indian ocean
Waratahs Occur in Eastern Australia, South America and Papua Guinea. This suggests that New Guinea and Eastern Australia are related to South America and its organisms across the Pacific Ocean
Galaxiid fishes Found in freshwater in temperate region of the southern hemisphere- in SA, NZ, New Caledonia, South America and South Africa
Continental Drift Drifting apart of land masses carried a diversity of living organisms that gradually evolved in isolation from one another Continents shift position over time as the Earth's crust is made up of large plates, carrying regions of both ocean and continent
Structural Morphology Comparative morphology (anatomy) is the comparison of equivalent structures in different organisms e.g. Human and chimpanzee (two arms, each with a hand a five digits, two legs, each with a foot and five digits.)
Homologous Structures Structures in different kinds of organisms that have a similar basic pattern even though they may serve a different function Provides evidence that the organisms shared a common ancestor from which they diverged over time (divergent evolution)
Analogous Structures Body structures that carry out a similar function but have evolved independently, therefore do not have a similar basic structure Organisms that display analogous structures cannot be assumed to have arisen from a common ancestor (convergent evolution)
Vestigial Organs Structures that organism’s possess that have no apparent function and that resemble structures found in other organisms Often remnants of organs that had a function in an ancestral species that have become reduced in size overtime or ceased to be used
Developmental biology (comparative embryology) Development of an embryo is controlled by a series of master genes that organise the position and a rate of growth of cells Organisms that shared a common ancestor often have similar master genes Embryos will pass through similar stages of development
Divergent Evolution Evolution of different species (populations) from a single common ancestral species Natural selection or genetic drift may lead to divergence of species or populations
Convergent Evolution Evolution through natural selection of similar features (analogous structures) in unrelated groups of organisms These species become more alike, or converge but still have other differences May occur from similar environments or lifestyles
Extinction Species that failed to adapt to environmental changes or to compete for limited resources can die out Result of changes in the physical environment Changes in the ecological interactions between species such as the arrival of new predator or competitor
Mass extinctions Large-scale extinctions following disruptive changes to the global climate, or loss of sea or land due to the shifting of continents
Created by: emmawalton05



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