Question

In the absence of microorganisms the earth would become a heap of dead plants and animals. Justify

Answer 1

microorganisms help in decomposing the dead and decaying matter. in their absence there will be no decomposition of Dead plants and animals and therefore the earth will become a heap of them

Answer 2

Dude I think you may know that we are all made up of cells which in short can be classified as microorganisms.
So if there are no cells, there will be no life.

Even if we leave multicellular organisms and focus on unicellular organisms, still every life form will be dead.