Week 3 - Dating Archives Flashcards
What are 3 types of dating?
Absolute dating
Annual increments
Age equivalence
What is annual dating?
Provides an absolute age (with uncertainties). Eg this sample is 8000 years plus or minus 250 years
Radiocarbon dating
What is annual increments dating?
Can provide absolute ages if you can fix one or more points with an absolute date or the present. Eg the outside of a tree is the fixed point because it is present day, then counting tree rings provides age
What is age equivalence dating?
Knowing that a point in one archive is the same age as a point in another.
What is radioactive decay?
Radioactive isotopes decay to form other elements
How do you find out the age of a parent radioactive isotope?
By measuring the number of half lifes
The half life of carbon-14 is ___ years
5730
What tool measures the decay of radiocarbon (carbon-14)?
An accelerator mass spectrometer (AMS)
A sample that contains little 14C will indicate…
That the sample is old
How far back can carbon 14 be dated back to?
50,000 years BP
In a lake, what is the difference between Uranium and Thorium?
U is more soluble than Th
Why might Th not be present in present day lake waters but present in old lake sediments?
Because U decays in Th, the more Th there is the older the sediment
In lake’s, where does Uranium come from?
Precipitated with calcium and incorporated into carbonate crystals
How are cosmogenic nuclides formed?
From bombardment of cosmic rays that hit the surface rocks
The more cosmogenic nuclides that rocks contain, the longer it has been ____ at the surface
Exposed
How far back can cosmogenic nuclides be dated?
Millions of years
What happens to the content of cosmogenic nuclides when a rock is exposed, buried, then exposed again?
Erodes away cosmogenic nuclides from the first exposure. But sometimes doesn’t get rid of all original cosmogenic nuclides
