Name:

Measuring Geologic Time (ES3B) Practice

U235 decay curve

I can explain the use of radioactive decay to date rocks. I can use Steno's laws, fossils, and radioactivity to estimate timing of geologic sequences.

  1. Explain what are index fossils and their value.
     
     
       
     
     
     
     
     
     
     
  2. A rock sample is found to have 25% of its U-235 left. How old is the rock sample?

     
  3. List the sequence of events (oldest to newest) that created this cross-section.

  4. In the cross-section above, how old is the siltstone layer E?