[Answer] How are the O and A horizons similar?

Answer: They both contain organic material.

Most relevant text from all around the web:

How are the O and A horizons similar? A soil horizon is a layer parallel to the soil surface whose physical chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features mainly colour and texture. These may be … The horizon is the apparent line that separates earth from sky the line that divides all viewing directions based on whether it intersects the Earth's surface or not.The true horizon is actually a theoretical line which can only be observed when it lies on the sea surface. At many locations this line is obscured by land trees buildings mountains etc. and the resulting intersection of ... Given the eye point O and β the plane parallel to α and lying on O then the vanishing line of α is β ∩ π. For example when α is the ground plane and β is the horizon plane then the vanishing line of α is the horizon line β ∩ π. Anderson notes "Only one particular vanishing line occurs often referred to as the " horizon ".: 249 ... The Canadian System of Soil Classification is more closely related to the American system than any other but they differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with the sub-order hierarchical level. Solonetzic and Gleysolic soils are differentiated at the order level. A Horizon label is an adhesive postage label that is a type of variable value stamp. The labels were introduced in the United Kingdom in 2002 [1] as part of the computerisation of the counter services of the post office network of Royal Mail using the Horizon System...

Disclaimer: 

Our tool is still learning and trying its best to find the correct answer to your question. Now its your turn, "The more we share The more we have". Comment any other details to improve the description, we will update answer while you visit us next time...Kindly check our comments section, Sometimes our tool may wrong but not our users.

Are We Wrong To Think We're Right? Then Give Right Answer Below As Comment