The question below consists of a set of labelled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.

P- On the earth, liquid forms and solid forms (ice/snow) predominate. 
Q- The water cycle has two distinct branches the atmospheric branch and the terrestrial branch. 
R- Water plays a versatile role in the functioning of the biosphere. 
S- In the atmospheric, water exists mainly in gaseous form.