what special quality does the asthenosphere have that allows the crust to float on it and be moved around ?

The tectonic plates do not slowly drift over time because they are floating on a layer of liquid rock. They drift because they are sitting on a layer of solid rock (the upper mantle or "asthenosphere") that is weak and ductile enough that it can flow very slowly under heat convection, somewhat like a liquid.

Explanation:

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.