Week 4 Flashcards
Relative Dating
Putting events in order without any numerical age assigned to them.
Absolute Dating
Calculating an exact date, we can do this with radiometric dating.
Lithostratigraphy
Study of rock layers in sedimentary rocks.
7 Principles of Relative Dating
Only work for sedimentary rocks
Superposition Original Horizontality Original Lateral Continuity Cross Cutting Relationship Principle of Inclusions Principle of Unconformities Principle of Faunal Succession
Principle of Superposition
Oldest layer is on the bottom
Principle of Original Horizontality
Sediments are deposited in horizontal layers, can be deformed later into folds or broken by faults.
Principle of Original Lateral Continuity
Continuous layers, you can trace undeformed layers from one rock outcrop to another, even when some of the layers have been eroded.
Principle of Cross Cutting Relationships
Any object that cuts across other object must be younger. Such as a dike.
Principle of Inclusions
If you have one rock that is surrounded by another, the included is the oldest. Rock surrounded by others had to exist first.
Principle of Unconformities
Rocks above an unconformity are younger than the rocks below. Unconformities mean there is time missing from the rock record.
Principle of Faunal Succession
Animals evolve and go extinct never to return again. Extinction is forever. Extinct animals only appear in rocks that formed when it was alive.
Biostratigraphy
Using fossils to tell time
Index fossils
Useful for correlating rocks of the same age
Widespread geographically
Existed for a short range of geologic time
Atoms
smallest unit of an element that still retains the properties of that element.
The number of ____ in an atom determine what an element is.
The number of protons in an atom determine what an element is.
Isotopes
atoms with differing amount of neutrons (hence differing mass numbers) but the same number of protons.
____ isotopes do not spontaneously break down.
Stable isotopes do not spontaneously break down.
____ isotopes break down over time.
Radioactive isotopes break down over time.
Radiometric dating is based on
known rates of radioactive decay to estimate the age of geologic samples.
Radiometric dating is measured using the ___ ___: the amount of time it takes for the sample to break down.
Radiometric dating is measured using the half life: the amount of time it takes for the sample to break down.
Do atoms decay at a constant rate?
No, we can only get averages.
In order to use radiometric dating there must be measurable quantities of
parent and daughter in the rock.
Is carbon an appropriate isotope for dating dinosaurs?
No, it’s life is too short and it can’t be measured reliably.
Are sedimentary or igneous rocks more appropriate for radiometric dating? Why?
Igneous rock is made up of one material, it is better for this kind of dating. Sedimentary rock is not as accurate because it’s made up of multiple minerals thus we can’t get an accurate reading on the rock as a whole.
