Sentence:  Of all the transitions brought about on the Earth's surface by temperature change, the <WSD>melting</WSD> of ice into water is the starkest. It is binary. And for the land beneath, the air above and the life around, it changes everything. 
Meaning of the word marked with <WSD> tags:  The process of changing the state of a substance from solid to liquid by heating it past its melting point.