fig. 8.16b
DESCRIPTION
Fig. 8.16b. Fig. 8.16a. Fig. 8.16c. CO 8. Fig. 8.1. Fig. 8.2. Fig. 8.3. Fig. 8.4. Fig. 8.5. Fig. 8.6. Fig. 8.7. Table 8.1. Fig. 8.8. Fig. 8.9. Fig. 8.10. Fig. 8.11. Fig. 8.23. Fig. 8.12. Fig. 8.18. Fig. 8.13. Fig. 8.14a-d. 0069. 0070. Fig. 8.14e. Fig. 8.15a-f. Fig. 8.15g. - PowerPoint PPT PresentationTRANSCRIPT
GEOLOGIC TIME
RELATIVE TIME
1. Original horizontality 2. Superposition 3. Cross-cutting relationships 4. Correlation
a. physical similarities b. use of fossils
index fossil = short-lived species that led to a more evolved species, widely distributed and plentiful
Fig. 8.16b
Fig. 8.16a
Fig. 8.16c
CO 8
Fig. 8.1
Fig. 8.2
Fig. 8.3
Fig. 8.4
Fig. 8.5
Fig. 8.6
Fig. 8.7
Table 8.1
Fig. 8.8
Fig. 8.9
Fig. 8.10
Fig. 8.11
Fig. 8.23
Fig. 8.12
UNCONFORMITY (missing time—rocks)
1. Dis-
3 and 4 missing
2. non-
3. angular
1 2 5 6
x x x x x x x x
x x x x
Fig. 8.18
Fig. 8.13
Fig. 8.14a-d
0069
0070
Fig. 8.14e
Fig. 8.15a-f
Fig. 8.15g
0071
0072
0068
0067
Fig. 8.17
Fig. 8.19
ABSOLUTE TIME
1. Radiometric dating requirements a. must have a radioactive
element (parent-P) that decays to a daughter element (D)
b. there is not removal or introduction of P or D
c. disintegration rate must be known and assumed to be constant over time
d. the half-life of the parent must be long enough to allow for age determinations (half-life = time for ½ of the P to disintegrate)
Fig. 8.20
Fig. 8.21
2. Examples of radioactivie methods
a. uranium decays to lead b. thorium decays to lead c. rubidium decays to
strontium
d. potassium decays to argon
e. carbon (14) decays to nitrogen
10 million to 4.6 billion years
500,000 to 4.6 billion years
100 to 70,000 years
1. radioactive carbon is formed when cosmic rays bombard nitrogen in the atmosphere
2. can be used only for
dating material that was once living
Example of dating method 1. assume that element
X has a half-life (t1/2) of 10 million years.
2. assume that
originally there was 100 million atoms of X present in a rock.
3. How old is the rock
if 6.25 million atoms of X is left?
Fig. 8.22
There are other absolute dating methods: 1. fission track dating 2. tree-ring dating 3. varve chronology
Atoms x 1 million of X Time (m.y.)
100 0 50 10
25 10 12.5 10 6.25 10
40
Age Era Period millions of years BP Cenozoic Quaternary 0.01 Tertiary 1.6 66.4 Mesozoic Cretaceous Jurassic Triassic 245 Paleozoic Permian Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian 570 Precambrian Proterozoic Archean 4600
Two eons—Precambrian and Phanerozoic
Fig. 8.24
Fig. 8.25
