William E. Ferguson Relative DatingRelative Dating Absolute DatingAbsolute Dating

Kelvin Calculation of Earth Age Kelvin Calculation of Earth Age

Unconformity Types Unconformity Types

Figure 8.1 Lab

Folding Rock Folding Rock

Relative Dating Principles Relative Dating Principles

Geologic Puzzle Time! - superposition, horizontality, cross- cutting relationships In assigned groups of 3, work out the age relationships in Figs in your lab book In assigned groups of 3, work out the age relationships in Figs in your lab book Pay attention to contact metamorphism! Pay attention to contact metamorphism! Use pencil!!!! Use pencil!!!! Put in squiggly lines between events for uncomformities Put in squiggly lines between events for uncomformities Be ready as a group to transfer your answers to an overhead & explain your relationships to the class. Be ready as a group to transfer your answers to an overhead & explain your relationships to the class.

Figure 8.4b

Figure 8.10b

Figure 8.9 Lab FBKNAJDMHCLGE

Figure 8.10a Lab GHIABCDLFEMJK Couldbeyounger

Figure 8.11 Lab SJKDXEAHMRBGPF

Figure 8.12 Lab RNHPDATFLGJZSBEKXMOCV

Radioactive Decay Radioactive Decay

What we need to know to apply radiometric dating The half-life of a radioactive isotope = time required for half of it to decay to a stable (non-radioactive) daughter isotope. 40 K decays to 40 Ar with half-life = 1300 million years. 40 K and 40 Ar can be measured in a mass spectrometer. 40 K is decaying to 40 Ar all the time, but 40 Ar is a gas and can escape if a mineral is above the “blocking temperature”. Below the blocking temperature, 40 Ar is trapped in the mineral. If a mineral is heated above the blocking temperature, 40 Ar is lost. Different isotopes (of U, K, Rb, Sr, etc) used in dating have different blocking temperatures. 40 K has the simplest decay scheme, and is the only one we’ll examine in detail.

# of Parent & Daughter Atoms as a Function of Time Parent Daughter

Proportion of Parent Atoms Remaining as a Function of Time Fig

Percent of Parent Atoms Remaining as a Function of Time

As more parent decays, the decay rate slows down, but the half-life doesn’t change Slope = rate of decay rate of decay Decay rate = P P = amt. Of parent = decay constant = decay constant = 0.693/half-life = 0.693/half-life