[kingwinner]

I am learning earth science and part of my notes say:

The earth, by physical properties, is divided into 3 key regions:
-lithosphere
-asthenosphere
-core

I don't understand why the earth is divided in this way.  And where does the mesosphere go? (lithosphere + asthenosphere + core isn't the "whole" earth)

Can someone answer me, please? I would appreciate for your *delete me*

[Mitch]

I don't understand why the earth is divided in this way.

I aggree with you. Why divide a pizza into toppings, crust, cheese, sauce and bread? Its just all one pizza afterall.