Adam and Eve were members of a modern-looking (by 20th century standards) society. While their contemporary civilization was progressing through exploitation of the planet's resources, the young couple were nature-lovers. They spend all their time by taking care of plant life. Seeing a flower grow was their greatest joy. The scientists of their time discovered the sun was growing cold and would become a death star within a short number of years. They would have to organize a planetary evaccuation for the human race to survive.
Over the following few years, humanity turnet all its effort to developing space-traveling technology. Adam and Eve were indifferent towards the developments. When rocket after rocket begun leaving the planet, the couple decided to stay. They would rather die with the planet instead of seeking safety among the stars. By their owmn decision, they were the last two humans left behind on the seemingly dying planet. They witnessed their sun dying. But also another sun born in its place.
Adam and Eve realized that the planet and all life in it would survive thanks to the new sun. They chose to rename their planet "Earth" and start their own breed of mankind.