As organisms die, their body breaks apart and may be used as nutrition for other organisms. Thier atoms are used to build another organism, and so on endlessly until life on Earth perishes. The atoms were created in the hearts of a star, which exploded and scattered the elements everywhere, the building blocks for life.
It is debatable whether or not you are/ were an onion. Your atoms might have once belonged to an onion. Who knows? You are, unchangeably, a Debatable Onion.
The Universe never ceases to amaze.