Part 2: Geologic time Relative dating methods: Using the diagram below, and the
ID: 110816 • Letter: P
Question
Part 2: Geologic time
Relative dating methods:
Using the diagram below, and the rules of relative dating, answer the following questions.
Which unit was being deposited when the fault happened?
Explain why the funny line between units 3 and 4 is a disconformity, and not an angular unconformity.
Hypothetically, if the trees and ground at the top were covered by the ocean, and deposition resumed, what type of unconformity would be above unit 12, and why?
Would unit 11 likely to be present when the fault happened? Why or why not?
Explain why units 1-5 were not deposited in this position.
In some areas, faults are known to act as a petroleum trap. If unit 2 has oil, and unit 3 is shale, what part of unit 2 would you drill into, above or below the fault, and why?
Radiometric dating:
Answer the following questions.
In order to ascertain useful dates on rock units to help determine the age of major events. Your mission is to date what is thought to be a very old fossil with a volcanic ash layer immediately above the fossil. We do know the fossil is at least more than 300 million years old. Should we use carbon 14 to date the fossil, or uranium 238 to date the volcanic ash layer, and why?
We find samples of an igneous rock demonstrate it has been through 3 half-lives. The test element has a half-life of 300 million years. How old is the rock?
If the parent isotope starts with 100 grams, but your samples yield only 6.25 grams of the parent isotope, how many half-lives have passed?
What unstable isotope would be best to refine the date of bones found in a cave hearth built by humans between 20,000 and 40,000 years ago?
Argue with the following: A stone tool fashioned from a chunk of obsidian yields a date of 3,000,000 years old, therefore, the tool was made by a human 3,000,000 years ago.
Explanation / Answer
1)Unit 10 was being deposited because it filled in more on the right side than on the leftdirectly above the fault....
2)If it were an angular unconformity, other units would be closer to unit 4. For example, unit 3 would be on the outer edges of 4 with unit 2 on the inside of unit 3, and unit 1 on the inside of that, allowing units 1, 2, and 3 to touch unit due to erosion.Instead, there is simply a missing period of time in which erosion rather than deposition occurred between units 3 and 4, indicating a disconformity...
3)An unconformity would result because the layer is currently in a period in which deposition is not occurring, leaving a gap between that layer and the next.....
4)No; the principle of crosscutting states that unit 11 would have had to be affected bythe fault if it was older than the fault. Because it was not affected, it is younger.....
5)The principle of original horizontality indicates that sediments are deposited in a generally horizontal manner until they are disturbed. Layers 1-5 were originally horizontal until they were uplifted or folded .