<span>Phoenixville, Pennsylvania </span>
Answer:
Potassium argon dating
Explanation:
Potassium argon dating is a method used in determining the origin of a rock. I is done by comparing the ratio of radioactive argon to radioactive potassium in the rock. This method is used to date rocks that are thousands of million years old.
the assumptions made when using the Potassium argon dating include :
- no argon was left after formation of the rock
- no argon has either entered or escaped the sample since it was formed.
Answer:
The mean center of population is the place where an imaginary, flat, weightless, and rigid map of the United States would balance perfectly if all residents were of equal weight. Historically, the movement of the center of population has reflected the expansion of the country, the settling of the frontier, waves of immigration and migration west and south. Since 1790, the center of population has moved steadily westward, angling to the southwest in recent decades.
SOURCE: Geography Division, "Centers of Population Computation for the United States 1950-2010," issued March 2011, available at www.census.gov/geo/www/2010census/centerpop2010/COP2010_documentation.pdf. Consulted for historical reference: Historical Atlas of the United States, National Geographic Society, 1988.
NOTE: The Proclamation Line of 1763 limited British settlement to areas east of the Appalachian Mountains. Alaska and Hawaii were not included in the calculation of the mean center of population until 1950. Puerto Rico was not included in any decade. For more information on the mean center of population, an animated map, and other resources. This graphic is adapted from the "Census Atlas of the United States" published by the Census Bureau in 2007.
Explanation:
