What is the theme in Life as We Knew It by Susan Beth Pfeffer?

Survival is the main theme of this story, as every person in it struggles to survive the crisis that happens when the asteroid hits the moon. At first it seems as though survival will consist of adapting to the changes in the world, and managing to hold on to enough food to last until things are sorted out again. However, it quickly becomes clear that this will not be nearly enough, and that it is going to be a very long time before life regains any sense of normalcy.