Dating of Rocks, Fossils, and Geologic Events


Assignment: Activity 2, pg. 167, Activity 3, pg. 169, Activity 5, pg. 171-172


Relative dating- Determining the age of something ________________ to the age of something else

  • Law of Original Horizontality- most rocks were originally laid down ___________
  • Law of Lateral Continuity- lava and _______________ rocks form a continuous bed
  • Law of Superposition- younger rocks are located _________ older rocks
  • Law of Inclusions- any rock fragment incorporated into another rock is ___________ than the rock it is found in
  • Law of Cross-Cutting- ANY feature (like a magma dike or fault) that cuts into a preexisting rock is ___________ than the rock it disturbs .
  • Law of Unconformities- gaps in the geologic record can be caused by ___________ or simply by a period of no deposition.
  • Law of Fossil Succession- knowing the age of a fossil can indicate its relative age in relation to other layers containing index ____________. An index fossil lived for a brief period of time and was widespread.

Absolute Dating- Determining the ____________ age of something.

  • Radiometric dating- finding the age of something by comparing the amount of radioactive isotopes to its stable _______ __________.
  • Parent Isotope- the _________ radioactive isotope
  • Daughter isotope- the stable ______ ___________ of decay
  • Half-life- The time it takes for ____________ of the parent atoms in a sample to decay to its stable end product. Surprisingly, the rate is predictable and uninfluenced by heat, sample size or pressure.