3. Geologists often cannot directly finding the ages of nearby rocks and applyin
ID: 290286 • Letter: 3
Question
3. Geologists often cannot directly finding the ages of nearby rocks and applying relative dating principles to minimum and maximum ages of the rock layer in question. date a rock layer, but instead have to "bracket" its age by determine the The diagram below shows a conglomerate layer (A) than can't be dated directly are a lava flow (B) and a dike (C), both of which can be dated. The analysis data tor ne igneous rock bodies which age is relative dating. also present are given on the next page. Calculate the ages of both, then determine the minimum age for the conglomerate and which is the maximum age by using Data Lava flow B: 50% uranium-235 50% lead-207 Dike C:60% uranium-235 40% lead-207 Half-lives elapsed Age Lava flow B: -years Dike C: years Minimum age of conglomerate A: years Maximum age of conglomerate A:yearsExplanation / Answer
Lava flow B
50% uranium 235
no of half lives = n
(1/2)n = 0.5
n = 1 half live
50% lead 207
Lead 207 is a stable nuclei it not undergo radioactive decay and so it hasnt any half life defined
half live of uranium 235 = 700 million years.= age of lava flow B
For dike C
60% uranium 235
no of half lives = n
(1/2)n = 0.6
n log(.5) = log (.6)
n = 0.7368
no of half lives = 0.7368
half live of uranium 235 = 700 million years.
so age of dike C = 0.7868 x 700 million years = 550.76 million years
HALF LIVES ELAPSED AGE
LAVA FLOW B 1 700 million years
DIKE C 0.7368 550.76 million years
Conglomerate A is deposited after the bed of lava flow B is deposited and after deposition of the conglomerate A, dike C is formed, so the conglomerate A is formed in between the depositional year of Lava flow B and the formation year of the Dike C
Minimum age of conglomerate A = 550.76 million years
Maximum age of conglomerate A = 700 million years
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