In TES Lore, Arkay is considered one of the youngest dieties. This is because his sphere - the cycle of life and death - didn't even exist until after the other seven divines created the mortal world.
Well, if that logic holds, then that begs the question of where Meridia came from. She is a Daedric Prince, meaning that her existence had to predate Nirn (that's the definition of Daedra: Those who didn't take part in the creation of Nirn), and yet, she dirives her power from the energy of living things.
However, such a distinction was never made prior to the creation of Nirn. So... where did her power come from beforehand?