10 Questions
What is a crucial factor to consider when selecting a radioisotope for dating a sample?
The isotope must be present in the sample to begin with
How many half-lives would be necessary for carbon to be an appropriate isotope for dating dinosaurs?
It would never be appropriate
What type of rocks can provide information about their formation time using radioactive isotopes?
Both volcanic and sedimentary rocks
What is the primary challenge when trying to determine the age of a fossil?
Dating the rock rather than the fossil
What is the purpose of the Geologic Time Scale?
To measure time on a large scale
Why is volcanic ash useful for dating rocks?
It contains radioactive isotopes
What is the age range of the dinosaur fossils?
228-65.6 Mya
What is the purpose of relative dating?
To determine the age range of a fossil
What is the significance of the Dorothy Bentonite?
It's a layer of volcanic ash
What is the primary concern when choosing an isotope for dating a rock?
The isotope must not decay too fast or too slow
Study Notes
Isotopes and Dating
- Geologists must choose an appropriate radioisotope for dating a sample, considering the sample's initial presence and measurable quantities of both parent and daughter elements.
- The selected isotope must have a decay rate that matches the expected age of the rock, neither too fast nor too slow.
- If an isotope decays quickly, there will not be enough parent left to accurately measure time.
Carbon Dating
- Carbon is not an appropriate isotope for dating dinosaurs (Fletcher et al., 2014).
Volcanic Rocks
- Volcanic rocks contain radioactive isotopes, allowing for the determination of their formation time.
- Sedimentary rocks can also contain radioactive isotopes, but the ages obtained represent the age of the mineral, not the rock.
The Dorothy Bentonite
- The Dorothy Bentonite is a 13m thick layer of volcanic ash located SE of Drumheller, dated to approximately 73 Ma.
Fossil Dating
- Relative dating techniques can determine the age range of a fossil (e.g., 228-65.6 Mya for dinosaurs).
- Absolute dating techniques require an appropriate isotope for the specific time range.
Geologic Time Scale
- The Geologic Time Scale measures time and is divided into smaller units (eons, eras, periods) based on the appearance or disappearance of different animals or groups of animals.
- The numerical ages of these units are determined using absolute and relative dating techniques.
- The farther back in time, the more distinct the animals appear, until no animals are present at all.
Learn about the principles of radioactive dating and how geologists choose the right isotope for dating rocks.
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