Dating Volcanic Rock
Explain the difference between?
Explain the difference between relative geologic age-dating and numerical (absolute) geologic age-dating. Include examples of techniques. Indicate which method is more useful in dating igneous (volcanic) rocks and which method is more useful in dating sedimentary (layered) rocks, and explain why.
Relative geologic age dating uses observations of factors related to a rock which allow us to make reasoned assumptions about the age of the rock compared to other rocks or its surroundings. Absolute dating uses knowledge about the decomposition of radioactive isotopes in the rock, then considering the half life of the isotope, allows us to calculate the age of the rock.
Relative dating is more useful in dating sedimentary rock. By examining the order of layers of sediment as well as the relative positions of the sediment layers, a deduction can be made about the age of the rock. Comparison to fossils in the sedimentary layers would also be helpful.
Igneous rock contains very accessible amounts of radioactive material in decomposition. By comparing the amount of a radioactive material (like Uranium) and the material it decomposes to (Lead) and considering the half-life of the radioactive material, the age can be calculated.
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