Birth of the Earth we see how the soil was formed. This occurred at around the same time that Higher Plants evolved. They evolved together. So did the soil animals. They all co-evolved and needed each other to create this new world of living soil. 

But how did this plant arrive. How did it grow up from what had gone previously - mainly ferns and mosses You can’t have a stem without roots. nor leaves without a stem, all differentiated cells working together. To produce strong structure that can reach the sun and suck up plant nutrients. But hwo did that come about?

From Essential Elements, we can see how these elements were essential for the development of seed bearing plants. Each of the four main differentiated cells root, stem, leaf and seed, require different essential elements to function properly. In order to evolve from big ferns into differentiated Higher Plants (those with distinct roots , stems, leaves  - and then seeds.  The mineral deemed essential to plant growth enabled plants to grow larger and live long enough to produce seeds. 

There essential elements have to be in the same place at the same time. And they are all in volcanic dust. And the seas in late Devonian were said to be over fertilised by volcanic ash and plant debris shows they were together in the same place and the same time. And there were a lot of volcanoes around at the crucial period. 

But let's not forget the soil animals. We know they were around then, but we have never pplugged theoir role into the coevolution of soil s and trees. Yet without the samllsoil creeatures, it could not have happened. The link between plants and soil is via the small soil animals. And part of that process was the role of soil animals that co-evolved to deal with the new environment being created We will have a look how they related with the development of Higher Plants..

Look at the following  
CLASSIFICATION to show how plat taxonomy /classification fits with the development of the Higher Plants
Many changes due to GOING TO GROUND 


And Role OF  SOIL ANIMALS in all this.

Perhaps this goes somewhere else..
Punctuated Equilibrium
This is a good excuse to bring a man who I have much respect for – the late Stephen Jay Gould. His theory of evolution is that evolution doesn’t happen gradually, but consists of punctuated equilibrium. That means most of the time nothing much changes – same environment, similar occupation of niches etc. But then ‘suddenly’ something happens to change conditions and creatures evolve relatively rapidly to fill the voids. The punctuated part here is from about 380 to 350 mya.

more on Devonian Explosion 

And so this event created new conditions, into which plants evolved, consisting now of differentiated parts – particularly stems leaves.. and roots. Soil animals could evolve rapidly too, some from the sea – springtails would groom the roots, eating dead fungi, encouraging fungal transmissions. Others – mainly mites, helped the fungi break the dead matter down which was then passed back via the fungi to the roots. Both these groups and the other main group of soil mesofauna – nematodes, are all pretty primitive creatures (pre-insecta). They colonised the volcanic dust and plant debris - before insects evolved (dragonflies, a pretty primitive insect evolved around 350mya). There was a relatively fast evolution in the soil parallel with tree growth. By the end of the end of the Carboniferous, there were tress everywhere (hence the name!). The development and spread of soil animals would have been in parallel, and explains why soil fauna are similar the world over..same three groups dominate. 

The development of insects was probably a way to avoid trying to colonise an already populated ecosystem. So they flew into the air. Virtually all insects are named after their wing parts, the common characteristic of insects.

If there was ever going to be a 'Punctuated' period of the equilibrium, then it could well be when two cotinents bump into each other for a 100 million years to make one continent. in the process volcanoes are common (why?) and they leave their ashes into which creatures from the water come and colonise, and evolve higher forms of plants aided by soil animals. The trigger was quite a short time - 10-15 mya that enabled/encouraged rapid development of plants and soil animals together, that goes on to this day.