Horizons as a vertical story.Wikimedia Commons, CC BYWhy this matters
A soil is a stack written by climate, organisms, relief, parent rock and time, not a single colour of mud. UK woodland and farm default is a brown earth: modest O, mixed A, a weak pale E, then B, C and bedrock. Yorkshire Dales soils over Carboniferous limestone are often thin; R is close to the boot. The US grassland pair is a mollisol: a thick dark A, little or no E, the prairie store that the Dust Bowl spent. An oxisol is the tropical end-member: deep, leached, red, not a Peak District peat. GCSE, A-level and APES all need named horizons. Geography posters that show one UK profile as universal leave a class unable to read a Great Plains pit or a laterite cut. The stack is the win because colour alone does not name a soil. O is litter. A is mineral mixed with organic. E is leached. B is accumulation. C is parent. R is rock. Say the letters before you say the place.
Field photograph or official scientific figure for teaching soil profile. A second photograph for the projector script — not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCThe mechanism
Horizons form because water, roots, fauna and chemistry move material down and sometimes up. Organic matter collects at the top as O, then mixes into A. In wetter, forested temperate climates clay and iron can be washed from an E horizon, leaving it paler; they accumulate in B. Grasslands keep adding roots and organic matter to A, so the dark layer thickens and E may never read. In hot, wet tropics intense leaching and oxidation build a deep red B and eat the rest of the story; nutrients sit in the biomass more than in the clay. Parent rock still matters: limestone in the Dales weathers to a thin rendzina-like cover; loess and glacial till on the Great Plains gave a deep mineral start. Time is a budget. A young dune has little profile; an old tropical surface has a thick one. This lab’s three slabs are types, not every soil on Earth. Brown earth, mollisol, oxisol. Name what is thick, what is missing, and what colour the B is. That is profile literacy: three climates, three stacks, not one UK pit drawn as the world.
How to drive the model
Scrub the Profile slider through 0, 1 and 2. Brown earth, mollisol, oxisol. Read the name and the note on the slab. Orbit so O sits at the top and R at the floor. Name each horizon out loud as the letters appear. Compare A thickness: thin-to-modest on the brown earth, thick and dark on the mollisol, thinner on the oxisol above a deep red B. Look for E: present and pale on the UK default, gone on the other two here. Step the camera to a side-on cut. Do not leave until the class can point at R and not call it compost.
If the model will not spin
Without the canvas the stack is still the lesson. O organic, A mixed mineral and organic, E leached, B accumulation, C parent, R bedrock. Brown earth is the UK woodland and farm default with a weak pale E. Mollisol is grassland with a thick dark A — Dust Bowl country when the cover goes. Oxisol is a highly weathered tropical soil, deep and red, not a UK peat. Yorkshire Dales limestone soils can be thin over R. Soil is not one kind of dirt. Horizons and climate write different profiles. Name the letters. Then name which layer is thick.
Film
What is Soil (and Why is it Important)? Crash Course Geography #16. Crash Course Geography. About 10 min. Crash Course / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off. Autoplay off.
Misconceptions
Soil is just dirt of one kind.
Horizons and climate write different profiles.
The dark layer is always the whole soil.
A is one horizon. B, C and R still sit underneath.
Every country has the same stack as a UK brown earth.
Mollisols and oxisols are different machines. Teach three, not one.
Horizon
A layer in a soil profile with its own colour, texture and chemistry.
horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCO horizon
Organic layer at the top: litter and decomposing material.
o horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCA horizon
Upper mineral soil mixed with organic matter. Topsoil in farm talk.
A horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. Upper mineral soil mixed with organic matter. Source: Wikimedia Commons / NASA / USGS / public domain.Wikimedia Commons / NASA / USGS / public domainE horizon
Eluviated, often paler layer from which clay and iron have been washed.
e horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCB horizon
Subsoil where materials accumulate. Colour and clay often change here.
B horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. Subsoil where materials accumulate. Source: Wikimedia Commons / NASA / USGS / public domain.Wikimedia Commons / NASA / USGS / public domainR horizon
Bedrock. Not soil.
r horizon in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCMollisol
Grassland soil with a thick dark A. Prairie and steppe store.
mollisol in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CCOxisol
Highly weathered tropical soil; deep, leached, often red.
oxisol in the soil-profile lab — a TERMS crop, not the glossary plate and not the lab cover. A TERMS crop, not the glossary plate and not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CC