How does this evidence indicate that the reaction has occurred between ions?

change of state of the reactants, e.g. precipitation.

Explanation:

The reaction of the ions can be checked by a number of methods. In a chemical reaction, the ions are in the acqeuos solution. This means that they are in solution, dissolved with charge. During the reaction (ionic) there is an attraction between the positive and negative ions. This makes a change in the state of the reactants in the products. In addition, the reaction can result in an immediate observable change such as the formation of a solid or precipitation.  

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.