What is the dark organic rich material formed as a top layer in soil from the decayed remains of plants and animals

Dark rich organic material formed as a top layer in soil from the decayed remains of plants and animals is called humus.  

Explanation:

When dead parts of plants and animals are deposited in soil the decomposing bacteria present in the soil act on these remains and break them down.  

Plant and animal bodies contain organic compounds which are broken down into inorganic nutrients by the decomposers. These nutrients are taken up by producers and the nutrients restart their journey in the food chain.  

Humus is identified by its rich dark color. The amount of humus decides how fertile the soil is. More the humus content fertile is the soil.  

carbohydrates: (starches and sugars) composed of carbon, hydrogen, and oxygen.

lipids: (fats, oils, and waxes) are made of carbon and hydrogen atoms.

nucleic acids: contain hydrogen, oxygen, nitrogen, carbon, and phosphorus. they are polymers of nucleotides. a nucleotide has three parts, a 5-carbon sugar, a phosphate     (-po⬇️4) group, and a nitrogenous base.

proteins: made up of nitrogen, carbon, hydrogen, and oxygen. they are polymers of amino acids.

most community's take hundreds of years to become stable