Geologic Time PreLab (#8 in Lab Text)
Name:_______________________________________
Briefly explain the difference between absolute and relative dating techniques.
According the law of original horizontality, if you encounter a dipping (tilted) sedimentary rock layer, you can conclude that the tilting occurred before / after (circle best answer) the sedimentary rock was deposited.
According to the law of lateral continuity, if you encounter a horizontal (non-dipping) sandstone layer in the field, this layer will probably / probably not (circle best answer) be present elsewhere as well.
According to the law of superposition, the sedimentary rocks at the bottom of the Grand Canyon must be older / younger (circle best answer) than the rocks near the top of the canyon.
According to law of inclusions, an inclusion of gabbro within basalt means that the gabbro is older / younger (circle best answer) than the basalt.
According the law of cross-cutting relationships, a diorite dike (sheetlike intrusion) would be older / younger (circle best answer) than the sandstone it intrudes.
Use Figure 8.1 as a reference for the following questions:
· Unconformities are surfaces of erosion or non-deposition that represent a __________ in the geologic (rock) record.
· Which type of unconformity is labeled “R” in Figure 8.9?
· Which type of unconformity represents the contact (geologic boundary) between Units A and J in Figure 8.9?
· Which type of unconformity occurs between Units C and D in Figure 8.2?
When radioactive parent atoms (isotopes) decay into a stable form, a new type of atom, called the _____________ isotope, is created.
Briefly explain the concept of half life:
As time goes by, the number of parent atoms within a crystal increases /decreases (circle best answer).
Use the charts in Figure 8.16 to estimate the percentages of parent and daughter atoms in a crystal after 3 half lives of time have elapsed: