About 400 million years ago a single celled algae began to cooperate with others of its kind to create larger, multicellular forms. Using the bacterial invention of cellulose for structure, the red, brown and green seaweeds evolved. They are not plants because they live surrounded by sunlight and water and dissolved nutrients, hence they have no need of leaves, veins or roots.
It seems that one type of seaweed, the Charophycaea, joined the soil community to create what we call plants. This algae created leaves that gathered sunlight above the ground, while being supplied with water from symbiotic fungi below the ground. Not too long after this the predator/prey relation came onto the land with the first arthropod mites, that sucked plant juices, and millipedes, that ate the mites.
Looking at soils nowadays we see that they are at least communities, possibly even entities. Plants in a developing soil spend their first years contributing excess carbon to grow the soil community in stages, not for their own growth. The soil acts like a decision-making entity. The plants may be looked at as parts of this entity. Even the animals that live from the plants in that ecosystem might be considered as parts of the soil entity.
Fungi in the soil community act as middleman between the plants, who need at least 16 specific nutrients, from nitrogen to zinc. Using sugars created by photosynthesis, the plants barter with different bacterial “companies” that specialize in supplying each one of these nutrients. Hundreds of different kinds of bacteria may be needed for each one of these “companies”. It becomes easier, then, to imagine how 10,000 kinds of bacteria (distinguished by metabolic niche) can be found in one cubic centimeter of soil. Plants themselves are more than genetic automata: they have behavior, make decisions and they communicate.
This first land community, based in the soil community, with simple plants and small arthropods was a stable entity. We will see it developing through several further stages.