Geologic Time

• what is stratigraphy?

  the study of rock layers
• what is palaeontology?

  the study of fossils
• what is relative dating?

  the principles of stratigraphy and palaeontology being used to determine the relative ages of rocks, sediments and landforms
• what are the four specific principles that reuse to build up the geologic timescale?

  principle of original horizontality , principle of superposition , principle of cross cutting relationships and the principle of faunal succession
• what does the principle of original horizontality refer to?

  sediments are deposited in horizontal beds or strata
• what does the principle of superposition refer to?

  each layer of sedimentary rock in a tectonically undisturbed sequence is younger than the one beneath it
• which principle refers to the idea that sediments are deposited horizontally in beds or strata?

  principle of original horizontality
• which principle refers to the idea that each layer of sediment in a tectonically undisturbed rock is younger than the one beneath it?

  the principle of superposition
• what does the principle of faunal succession refer to?

  the idea that the sedimentary strata in an outcrop contain fossils in a definite sequence
• which principle refers to the idea that sedimentary strata have definite sequences of fossils within?

  Principle of faunal succession
• what does the principle of cross cutting relationships refer to?

  an igneous intrusion must be younger than the rocks which it intrudes and a fault must be younger than the rocks it cuts
• which principle refers to the fact that a fault must be younger than the rocks it cuts and an igneous intrusion must be younger than the rocks it intrudes?

  principle of cross cutting relationships
• what are the two groups in which fossils can be divided into?

  body fossils and trace fossils
• what are body fossils?

  shells, teeth, bones, impressions of plants etc
• what are trace fossils?

  records of biological activity such as footprints or burrows - there is no impression from the actual organism itself
• what is the difference between absolute dating and relative dating?

  absolute dating provides numbers rather than just a relative order of age
• what needed to be discovered in order for radiometric and isotopic dating techniques to be introduced?

  radioactivity
• who was the first person to use absolute dating?

  Ernest Rutherford in 1905 - calculated the age of a rock from its Uranium content
• what does the isotopic dating procedure use?

  a mass spectrometer
• what does a mass spectrometer count?

  daughter atoms
• how does a mass spectrometer work?

  it counts the daughter atoms and knows the rate of decay, allowing it to calculate the time when there were no daughter atoms - this gives us the time of the formation of the rock
• what does the isotopic age of the rock tell us?

  the time since the isotopic clock was 'reset' = when the isotopes were last locked into the minerals
• how can isotopic dating be used in sedimentary rockss?

  dating the time of death of organisms
• how can isotopic dating be used in igneous rocks?

  dating the time of cooling and crystallisation of magma
• how can isotopic dating be used in metamorphic rocks?

  dating the time elapsed since metamorphism
• what is the unit for one billion years?

  giga-annum (Ga)
• what is the unit for one million years?

  mega-annum (Ma)
• what is the unit for one thousand years?

  kilo-annum (ka)
• what is the unit for one year?

  annum (a)