Geological Dating (323 – 333)
Relative Age – The approximate age of a rock layer or
fossil determined by the age of the layers or fossils above
or beneath.
Law of Superposition – A layer of sedimentary rock is
older than the layer above it
Ex.
Exceptions:
1) Rocks may be folded , tilted , or overturned out of
position
2) Faults may push rock layers out of position
3) Intrusions of magma may cut through rock layers
4) Weathering may cause gap in order of layers
Absolute Age - This is the actual age of a substance.
This is measured by using the half life of radioactive
elements.
Radioactive elements - These are isotopes (varieties of
certain elements containing different masses) of elements
whose nucleus is decaying (breaking down, releasing
energy and particles at a constant rate).
EX. Uranium 238 Carbon 14
- The number stands for the mass of the isotope
- Uranium decays until it reaches lead 206. When an
element stops decaying it is considered stable.
Half Life - This is the time it takes half the mass of a
radioactive isotope to decay into its stable form.
(See example)