Images of light and darkness fill the play.  Romeo constantly refers to Juliet as a form of light (i.e. the sun).  Juliet also refers to Romeo as light, light that illuminates darkness.  She wants him to be cut into little stars after death so the world will be in love with night. (III.2) The darkness shields their light, their love, from the eyes of their families. 

The earth that's nature's mother is her tomb.

What is her burying grave, that is her womb (II.3)

Life and death are simply part of the continuous cycle of earth.  Everything is born from the earth and must eventually return to it. 

Death itself is a prevalent image in the play.  Capulet refers to death as a bridegroom who has deflowered his daughter and spirited her away against his will.  (IV.5) Romeo presents a similar image in Juliet's tomb when he refers to death as her paramour (V.3.105). When Romeo first arrives at Juliet's tomb, a house of death, he sees it as a monster.  He says Thou detestable maw, thou womb of death, Gorged with the dearest morsel of the earth, Thus I enforce thy rotten jaws to open, And in despite I'll cram thee with more food. (V.3.45-48) Death consumes its victims and in this case, Romeo's lover.  For Romeo, Juliet is the most important (dearest morsel) on earth and death has swallowed her.  He presented a similar image in Friar Lawrence's cell while awaiting Juliet.  He challenged love-devouring death to try to destroy his joy.