Fill in the Blanks :
1. Environment has been divided in ......... spheres.
2. The SIAL layer of the earth is made up of the material which is rich in and ..........
3. The SIAL layer of the earth is made up of the material which is rich in ............. and ..........
4. The different types of species of animals is known as ..........
5. portion of earth has been covered by hydrosphere.