Sentence:  The men and women of the Renaissance period likely had little inkling of the truly titanic changes that were unfolding around them, let alone the ability to predict where it would all end up. Nevertheless, many of their legacies remain with us today: the birth of modern nation-states; the expansion of political rights and freedoms; the rise of the university, the media, and the industrial corporation; and a <WSD>Cambrian explosion</WSD> of science, medicine, knowledge, and cultural expression. 
Meaning of the word marked with <WSD> tags:  The rapid appearance of anything.