O Horizon (Organic)
The uppermost layer consisting of freshly fallen leaves, twigs, animal waste, and fungi. As it decomposes, it forms a dark, crumbly material called Humus, which coats the topsoil below.
AP Exam Mnemonic
"Only Ants Eat Bread Crumbs Regularly"
O, A, E, B, C, R. Note that E (Eluviation) is the zone where minerals exit (leach out) due to acidic water, leaving it pale. B is where those minerals accumulate.