Answer: Land: Denser materials sank to the earths center and less dense materials were forced to the outer layers, forming a thin crust. Atmosphere: Less dense molecules rose to the surface. Oceans: As earth cooled, water vapor condensed to form rain which lead to the formation of oceans.
Chemical reactions occur when chemical bonds between atoms are formed or broken. If this is what you mean because the question is really confusing sorry :(
The gene pool.
all of the alleles in a population are it's gene pool
