Noun
the top layer of a soil profile; usually contains humus
Source: WordNetA-horizon
After sufficient time, humus moves downward and is deposited in a distinctive organic surface layer called the A horizon. Source: Internet
A horizon line is placed at its center—tapping an area above it sets the drone on a path toward that object while ascending, and tapping below it moves the Phantom in that direction while descending. Source: Internet
Commonly found on unconsolidated river and beach sediments of sand and clay or volcanic ash, some have an A horizon on top of bedrock. Source: Internet
The cycles of evolution of soils have very variable durations, between tens, hundreds, or thousands of years for quickly evolving soils (A horizon only) to more than a million years for slowly developing soils. Source: Internet