Here's why:
* Composition: The O horizon is primarily made up of decomposing plant and animal matter, like leaves, twigs, and roots.
* Formation: This layer forms directly on the surface and is constantly being replenished by new organic matter.
* Decomposition: As organic matter decomposes, it breaks down into smaller particles, contributing to the formation of the underlying layers (A horizon and below).
It's important to remember that soil formation is a slow process, and the O horizon is constantly evolving as new organic matter is added and existing material decomposes.
