When defining concentration during diffusion, what exactly are we describing?​

The amount of a substance in relation to the total volume is the concentration. During diffusion, molecules are said to flow down their concentration gradient, flowing from an area of high concentration to an area of low concentration.

this age may represent the age of the earth's accretion, of core formation, or of the material from which the earth formed. this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.