Evolution — BIOLOGY STD 12 Science — Question

1. 22.5km

Explanation:

Moving from centre to surface, earth can be divided into three major layers namely; the core, the mantle and the crust. Core is the deepest and hottest layer of earth; the outer core consists of iron-nickel alloy along which small amount of heavy metals while the inner core is made up mostly of iron.

The higher temperature, 7000-9000°F keeps the outer core in liquid state while higher pressure on inner core keeps it in solid state despite the high temperature conditions. Thickness of outer and inner core is 2259km and 1221km respectively.

Mantle is 2900km thick layer wherein most of the earth’s internal heat is located. The outer most layer of earth is crust; it is 22.4km thick and forms the only habitable part of earth. It comprises continents (lithosphere) and ocean basin (hydrosphere) that support life.