Absolute Dating
The process used to determine a precise age of fossils and rock
What is absolute dating?
A surface where rock layers were first eroded away, then new deposition was placed over this surface. It represents a gap in the rock record.
What is an unconformity?
A sample was taken from a fossil and it was found that 50% of the fossil contains Carbon-14 (half-life of 5,750). How old is the fossil?
What is 5,750 years old
The unstable elements found in fossils
What are radioactive isotopes?
A special type of fossil that was widely distributed, common, and lived for only a short period of time.
What is an index fossil?
A sample of wood found in an ancient tomb contains 25% of its original carbon-14. The age of this wood sample is approximately _______________.
(half-life of 5,750 years)
What is 11, 500 years old? (5,750 X 2 half lives)
This principle of relative age dating states that layers of sediment are originally deposited in flat, horizontal sheets. Even if layers tilt due to uplift, they were originally flat
What is the Law of Original Horizontality?
This type of unconformity is where sedimentary layers are deposited on top of older, horizontal sedimentary layers that were eroded.
What is a disconformity?
A radioactive isotope under goes a half life every 22 years. This much of the original isotope would remain in a 20 gram sample after 66 years.
What is 2.5 grams? (3 half lives; 1st-10g, 2nd-5g, 3rd-2.5g)
This principal states that sediment is deposited in a continuous sheet until the amount thins out or hits a barrier.
What is the Law of Lateral Continuity?
You start with 200 g of radioactive isotope Y. If isotope Y has a half life of 14 years, it would take ________ years to decay and be left with only 25 g of material.
What is 42 years? (200->100->50->25; 3 half lives. 3 x 14 = 42).
This elemental isotope is only used to date matter that was once living. The amount of this radioactive element begins to decrease the moment the organism dies, so any age determined with this isotope is from when the fossil died.
What is Carbon-14
In this picture, it is the youngest feature of these rock layers.
What is the Fault?
Magma pushes through sedimentary layers, eventually crystallizing into this type of rock, forming a dike.
What is igneous rock?
A sample of carbon-14 under goes 3 half lives. This percentage of the sample has decayed into a stable daughter isotope?
What is 87.5%