Chronostratigraphy Flashcards
(14 cards)
What are 6 purposes to the Geological Time Scale?
- Express any age in any place
- Express broad and general ages and particular and detailed ages
- Understandable and unambiguous
- Objective reference
- Not subject to frequent change
- Used internationally
What are the 2 fundamental types of isochronous units?
- Chronostratigraphic units
- Geochronologic units
What is the hour glass theory?
The theory that chronostratigraphic units represent the volume of sand passing through the hour glass in a given time and the geochronologic units representing the duration of time the sand passes through
What is chronostratigraphy based upon?
Based upon data derived from multiple diachronous stratigraphic units
What does geochronologic units represent?
The interval of time during which the chronostratigraphic units were deposited
What 2 fundamental stages were taken to construct the chronostratigraphic scale?
- Determining time-stratigraphic relationships
- Using local strat as a basis of finding a composite international chronostratigraphic scale
What are 2 ways that the geological time scale was calibrated?
- Arranging rocks in an orderly succession using relative position
- Determining actual numerical ages of boundaries between rock units
How can you get the precise numerical ages?
- Counting backwards using repetitive annual time markers
- Counting from a defined point using astronomical events
Why is radiometric decay of unstable isotopes an imprecise numerical dating technique to use?
- Dates aren’t directly lined to the present day or an absolute known date
- Due to decay rates, there are error margins in dates
What does half life measure?
A measure of the limits of the various isotopic systems
What if the half life is too short? What does it tell you about the method?
The method is limited to relatively recent times
What if the half life is too long? What does it tell you about the method?
There will be an insufficient decay to measure
What are 5 assumptions that are essential to radioactive decay
- Constant decay rate
- Decay rate just must be measured
- Parent and daughter isotopes are to be remained in a closed system
- None of the decay products is in the system at the start
- Using a mass spectrometer, isotope ratios can be measured accurately .
What’s now the appropriate technique used to employ depends on.. 2)
- Radioactive elements present in units
- How sensitive a time measurement is
