Earth formed about 4.6 billion years ago during the birth of our solar system. ... During the next major phase of earth's formation cooling and differentiation of the Earth's layers occurred. Dense materials sank to the center, forming an iron-nickel rich core. Lighter buoyant silicate-rich magma rose to the surface.
Deserts are a natural barrier between regions, they are difficult to travel through safely due to harsh conditions. Transport of goods and people is more costly and more difficult.
