Isostatic rebound occurs when load is added or removed on the lithosphere and the surface either sinks or rises under the weight of the asthenosphere.
At first, when load which can be in form of glacier is added to the lithosphere, this block of the earth would sink rapidly at first due to the added weight. With time, as the adjustment continues, an equilibrium is now reached between the lithosphere and the asthenosphere. At this point, the asthenosphere would have gathered enough strength to carry the overlying weight.
absolute age(true age) The age of a geologic phenomenon measured in present Earth years, rather than its age relative to other geologic phenomena (compare relative age)
