The movement of material due to differences in density is called?

This movement is called convection. It can be found in liquids, gasses and rheids - solids that can also experience movement ( on a big time scale), such as the earth mantle. One of the types of convection is diffusion: net movement of gasses from higher to lower concentration areas.

Physics and astronomy were developed in babylonia.

Using scarce resources today means having fewer tomorrow, businesses can only make a limited number of goods and services, and not everyone's needs are met.