Hi there I'm having trouble with this study guide. Could someone please help me?
You’ve returned from a recent geologic expedition and discovered that the security at the airport has dumped out all of your carefully sorted rock samples into a heap. You need to quickly sort the rocks by age. The first rock, sample A, has fossilized footprints from some kind of a mammal. Sample B contains shark teeth and shells. Sample C has a perfectly preserved specimen of Phacops rana and sample D has half of Chonetes. How do you rank your samples from oldest to youngest?
ii. What are the absolute ages of your samples?
iii. Did amphibians evolve into dinosaurs?
iv. From all of the choices listed in this lab, which animal has been around for the longest amount of time? Which has been around for the shortest amount of time?
5. You have a sample of rock that contains 91.7% Uranium 235 and 8.3% Lead 207. How old is this rock?
6. You have a document that has 1.1 Nitrogen-14 content, how old is it?
7. Why isn’t it a good idea to use Carbon-14 dating to date rocks?
Sure! I'd be happy to help you with your study guide. Let's go through each question one by one:
i. To rank the rock samples from oldest to youngest, you need to consider the principles of relative dating. These principles include the law of superposition, which states that the oldest rocks are found at the bottom of a sequence, and the principle of faunal succession, which states that fossils found in rocks can be used to determine their relative ages.
Based on the information given:
- Sample A contains fossilized footprints of a mammal and does not have any other specific fossils mentioned. This indicates that it is the youngest sample, as it contains the most recent fossil evidence.
- Sample B contains shark teeth and shells, which are typically found in marine environments. Since marine organisms have been evolving for a long time, this suggests that Sample B is older than Sample A.
- Sample C contains a perfectly preserved specimen of Phacops rana, which is an extinct trilobite species. Trilobites are known to have lived during the Paleozoic Era, which is older than the time when mammals and sharks existed. Therefore, Sample C is older than Samples A and B.
- Sample D has half of Chonetes, which is a type of brachiopod. Brachiopods have been around for a long time, but they are not as old as trilobites. Therefore, Sample D is younger than Sample C.
So, based on this information, the rock samples can be ranked from oldest to youngest as follows:
1. Sample C
2. Sample B
3. Sample D
4. Sample A
ii. To determine the absolute ages of the rock samples, you would need to use radiometric dating, specifically methods that rely on radioactive isotopes. Unfortunately, the given information does not provide any radioactive decay calculations, so we cannot determine the absolute ages of the samples.
iii. The question of whether amphibians evolved into dinosaurs requires a broader understanding of evolutionary history. Amphibians and dinosaurs are two different groups of organisms that evolved along separate evolutionary paths. Amphibians are ancient vertebrates that evolved around 360 million years ago, while dinosaurs evolved later. Dinosaurs, specifically the non-avian dinosaurs, existed during the Mesozoic Era, which started around 252 million years ago. So, while amphibians and dinosaurs are part of the broader evolutionary tree of life, amphibians did not directly evolve into dinosaurs.
iv. The question asks about the animal that has been around for the longest and the shortest amount of time based on the choices given in the lab. Unfortunately, the lab choices are not specified, so we cannot provide a specific answer.
5. To determine the age of the rock sample that contains 91.7% Uranium-235 and 8.3% Lead-207, we can use the concept of radioactive decay. Uranium-235 decays into Lead-207 with a known half-life of 704 million years.
To calculate the age, we need to determine the number of half-lives that have elapsed. Since the ratio of Uranium-235 to Lead-207 is approximately 91.7:8.3, it means that almost all of the Uranium-235 has decayed into Lead-207. This corresponds to one half-life, as half of the original Uranium-235 has decayed.
The half-life of Uranium-235 is 704 million years, so the calculated age of the rock sample would be approximately 704 million years.
6. The question mentions a document that has 1.1 Nitrogen-14 content and asks for its age. However, the given information is not sufficient to determine the age. Age determination typically involves using radioactive isotopes with known decay rates, but no such information is provided in this question.
7. Carbon-14 dating is not typically used to date rocks because the half-life of Carbon-14 is relatively short (approximately 5730 years). This makes it suitable for dating organic materials, such as remains of plants and animals, rather than inorganic materials like rocks. Additionally, Carbon-14 dating is useful for determining ages up to around 50,000 years, but it becomes less reliable beyond that timeframe due to decreasing amounts of Carbon-14 and difficulty in accurate measurement. Therefore, for dating rocks that are millions or billions of years old, other radiometric dating methods with longer half-lives, such as uranium-lead or potassium-argon dating, are preferred.
I hope this helps! Let me know if you have any further questions.