Define radioactive decay and describe how half-life is used to determine the geologic age of a rock.

Explained as below

Explanation:

Radioactive decay is known as nuclear decay, nuclear disintegration. Is the process by which unstable atoms losses energy such as alpha and beta particles.  Since 1950's geologists are using radiometric dating s to define the age of rocks over the earth as natural clocks for determining the natural age of rocks. It is a valuable tool for measuring the absolute age of rocks. Using Carbon  14 which has a half-life of 5,730 years decays into nitrogen. This method uses traces of atmospheric carbon dioxide. As most of the matter in the world is made up of carbon particles hence evaluating them is quite easier.  This method is also used to study the local eruption of volcanoes and other changes in the internal structure of the earth. At places, chlorine 36 dating has been used for geologic water and ice sediments.

Answer after wwii, communist countries in eastern europe formed the warsaw pack, a military alliance, and comecon, an economic alliance;

The answer is d. none  hope this .