Give geographical reasons - There is correlation between the density of metals and their location in the interior of the earth.
Answers
It has been discovered that the location of metals found in the crust of earth is closely related to their density and chemical properties.
It is based on the principle of buoyancy and floatation in fluid dynamics.
Higher the density of the metal, farther away it will be found from the surface of earth. This is because lower density metals floated towards the surface of earth during the formation of the crust, while metals with higher density were pushed closer to the mantle.
Geoscientists have presented a number of factors for the occurrence of different metals in the different layers of earth. Two important phenomena associated with such arrangement of metals in the different layers are-
1. Planetary differentiation
2. Iron catastrophe
Both of these are interrelated and give a satisfactory explanation for the occurrence of metals in the different layers of earth. When earth formed about 4.5 billion years ago, it was no better than a ball of hot rock. The interior of the earth was too hot and the temperature went on increasing further. A notable change was observed when this temperature reached the melting point of iron and the iron in the core started melting. This is commonly referred to as iron catastrophe.
As the temperature reached the melting point of iron, the molten material which consisted mostly of iron started flowing at a faster rate. This flow also resulted in the lighter elements flowing towards the top i.e. the exterior of earth. Air (that formed the atmosphere), water (that formed the hydrosphere) and silicates were among the comparatively lighter elements that flowed towards the crust and became crucial elements for both, formation and sustainability of life on earth’s crust.
On the other hand, heavier metals like iron and nickel, gravitated back towards the core. The earth’s core is popularly referred to be composed of NiFe. This movement of metals to the different layers of earth is called planetary differentiation.
It also accounts for the fact that the present day crust and mantle are mostly rich in minerals while the core is mainly composed of iron and also provides for the geomagnetic field of earth.