Soil Horizons and atmosphere

O Horizon

The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter.)

A Horizon

The layer called topsoil; it is found below the O horizon and above the E horizon. Seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.

E Horizon

This eluvation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips throughout he soil (in the process of eluvation).

B Horizon

Also called the subsoil - this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.

C Horizon

Also called regolith; the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate to this layer; very little organic material is found in this layer.

R Horizon

The unweathered rock (bedrock) layer that is beneath all the other layers.

Exosphere

The outer layer of the thermosphere, extending outward into space.

Thermosphere

The uppermost layer of the atmosphere, in which temperature increases as altitude increases

Mesosphere

The layer of Earth's atmosphere immediately above the stratosphere

Stratosphere

The second-lowest layer of Earth's atmosphere.

Troposphere

The lowest layer of Earth's atmosphere