here are majorly 12 factors influence Soil fertility
Infiltration of water.
Soil structure.
Active Soil life.
Content of organic matter.
Minerals present in the soil.
Acidity or Soil pH.
Water Retention capacity of soil.
Water draining ability of the soil.
(google)
It is called hydrosphere
It is the total water in Earth.
Each layer of earth has a different density the more in you go with the layers the more density is going to show up.
Crust-2.2g/cm^3
Upper mantle-3.4g/cm^3
Lower mantle-4.4g/cm^3
Outer core-9.9g/cm^3
Inner core-12.8g/cm^3
Hope I helped in something, Sorry if I didn't gave it my best shot:)
