Wow Severa, indeed a fun and very thought provoking question!  Eternity to me means a timeless existence.  Eternity has no beginning and no end.  I believe everything is energy (I call it God energy).  Call it cosmic energy, divine energy, universal energy, regardless of ones' preference; it is energy, which has no beginning and no end.  Energy cannot die or sieze to exist.  Since everything is energy, everything can change forms, but the energy continues to exist.  For example: a plant may die, the energy does not die, it changes the form of energy in the plant.  The plant is actually still alive in a different form of energy.  A cloud energy can change to rain energy to moisture energy in the ground to condensation energy and reform new cloud energy.  A tree can die, the energy does not die; it changes the form of energy of the tree, for example to petrified wood; which is still energy.  Even when a person dies, the energy changes forms, the physical remains turn to dust energy, the soul energy continues (one just has to have experienced energy of a souls' presence to recognize the soul energy continues to exist).  Does this prove anything?  I do not have the answer, but unless proven otherwise, this is what I know for now.  LOL, the awesome wonder of it all is an eternal journey.