Answer:
Radioactive isotopes are unstable and will decay. ... The isotopes will decay into a stable isotope over time. Scientists can tell how old the rock was from looking at the radioactive isotope's half-life, which tells them how long it would take for there to be half the radioactive isotope and half the stable isotope.
A metropolitan area.
Example: New York Metropolitan Area
Australia is primarily influenced by the western culture of Britain, so I'd say European. Although they also have some Pacific Islander influence.