Life on earth (L1)

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How was the earth formed?
4.54 billion years ago there was a collision with another photo-planet 'the' and the mood was formed, earth cools down and water arrives from volcanoes
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How can isotopes be used to date samples?
Radioactive carbon (C14) decays to nitrogen with a half life of 5,700, useful for carbon dating up to 60,000 years but is no use for dating over geological timescales
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What isotopes can be used to date samples?
Only isotopes with a large half life (100-4.5 billion years)
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Why can sediments not be aged by radioactive decay?
Because relative dating is to determine the sequential order of the layers of rock, not the actual age
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What are layers of rock called?
Strata
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How can relative ages of rocks be determined?
By looking at strata of undisturbed sedimentary rock
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Describe the law of superposition
The law states that a sedimentary rock layer that is undisturbed is you're than the layer below it but older then the one above it
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What is the principle of lateral continuity?
Layers of sediment are laterally continuous (in age etc)
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What is a problem with the principle of lateral continuity?
Compression can cause thrusting of older rocks over younger ones, further compression can lead to the rocks being folded into an anticline (upfold)
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What does the principle fo Faunal succession use?
Uses fossils for relative dating of sedimentary rocks
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What are fossils?
Transformed remains or impressions of organisms, some biological materials decompose very slowly (e.g. calcium carbonate- shells or chitin- arthropod exoskeletons)
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Describe the process of fossilisation
Diagenesis (chemical and physical change of sediment to sedimentary rock) modifies the remains, replacing them with highly insoluble minerals (anaerobic bacteria reduce SO4*2- to S*2-, forming pyrite, CaCO3 may be replaced with pyrite or silica
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What is stratigraphy?
A geological method where fossils are used to age sedimentary rocks, certain fossils are always found in younger strata and others in older
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What do fossils indicate?
How continents were once connected, how environments have changed through geological time, how organisms have evolved
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Why are ammonites good for stratigraphy?
They evolved rapidly so each species have a relatively short time span, found in many types of sedimentary rock, common and easy to find, have a worldwide geographical distribution
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How did oxygen levels rise?
2.5bya oxygen began to rise as a by-product of Cyanobacteria, world wide iron deposits give us evidence for this
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How did continental drift result in environment change?
Because continents moved closer or further away from the equator (ice-ages and extraterrestrial impacts have also caused environmental change)
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How many major ice ages have there been?
6
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Give an example of how ice ages can change the environment
Sea levels from and it causes loss of a lot of marine life (e.g. 440mya sea levels dropped 50-70m causing mass extinction of 75% of marine forms)
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What else caused mass extinctions?
Large meteorite impacts causing intense heat, tsunamis and chemical fall-out signature
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Other cards in this set

Card 2

Front

How can isotopes be used to date samples?

Back

Radioactive carbon (C14) decays to nitrogen with a half life of 5,700, useful for carbon dating up to 60,000 years but is no use for dating over geological timescales

Card 3

Front

What isotopes can be used to date samples?

Back

Preview of the front of card 3

Card 4

Front

Why can sediments not be aged by radioactive decay?

Back

Preview of the front of card 4

Card 5

Front

What are layers of rock called?

Back

Preview of the front of card 5
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