With increase in the depth of the soil the temperature of soil also get increases due to high pressure present deep in the earth.
With high temperature, the metal that having high melting point such as heavy metals are present which includes lead, chromium, arsenic, zinc, cadmium, mercury etc. With incresae in depth the soil get contaminated with these heavy metal or the concentration of heavy metal may increases in soil with increase in depth which may result in low fertility of soil. Heavy metal also increases toxicity of the soil which affect the growth of crops and plants by harming the roots of flora.
Certain bacteria such as thermoacidophilus also present at this depth fo earth as they can survive in this range of temperature.
Thus, the condition of soil present more than 50 km deep in earth is not good in comparison to fresh soil present on surface.
