Liverworts and mosses had been joined by ferns and horsetails as well as seed-bearing plants called gymnosperms, like conifers and ginkgos. They covered more land, trapping more energy from the sun.

Their roots would have been shallow and their debris would have been predominantly cellulose with little lignin. More on plants

Small legged creatures were running round, probably passing spores, but also eating fungi and debris, and pooing out the remains, which happen to be adhesives sticking various bits of debris and minerals together.

The three key small animals are all over the world are the springtails, mites and nematode 

Many of them are considered to be ‘generalistic’, in that they may have a primary preference for what to eat but will eat alternatives. While some are predominantly fungal eaters, they can change to eating debris and are not that fussy. They can make do with a wide variety of food, rather than specific to a particular group. This has stood many early soil inhabitants well over many difficult years. 

Some springtails look like living fossils from 400 mya. The mycorrhizal fungi are found on 80% of plants roots. These processes are much the same today, while roots and environmental conditions have changed. It is probably the most important process ever of life, having evolved all this time ago, adapted throughout hundreds of millions of years, and today hold the key to improve soils. Animals

The 3-way process between roots fungi and springtails is the most important building process of the soil and emerged during this period. It is aerobic requiring oxygen to function. All else has been built upon it, and it is still today one of the most vital life processes on earth. 

Roots of plants produce exudates which make their surrounding attractive to mycorrhizal fungi. Root exudates may act as signals for microbial recognition. Some’flavonoids’ may be suppressors of certain pathogenic fungi. Root exudates can also indirectly suppress pathogens by attracting antagonists of plant pathogens. Strigolactones are carotenoid-derived signalling molecules and released from roots that enable symbiotic fungi to detect their host plants and have been identified in AM fungi and can induce AM spore germination and hyphal branching (Marschner, 2019). 

The fungal filaments provide the roots with much more water and nutrients particularly phosphates. In return the roots provide the energy for fungi. The fungi produce glomalin, discovered about 30 year ago, which makes up a quarter of all soil carbon, and is the main food for springtails, often around 100,000 per sqm. This vast number chew the glomalin and poo it out as glomalin related soil proteins (GRSPs). This spreads the carbon compounds, captured in the leaves conducted into the roots, throughout the soil. The springtails also help distribute the fungal spores and keep the roots clean of dead fungal matter.  GRSPs are gluey substances which bind together various mineral and vegetable particles to make the aggregates which provide the pores for life and holding water.

Spores are the main spreaders for plants fungi and bacteria. Spores are asexual and take less energy to produce than a seed. Spores do not vary a lot, but in those times, it did not require variation to adapt to conditions because there was a lot of land open to anything which could survive. The distribution of spores – of plants, fungi and bacteria, must have been monumental. The structure of these spores must have been crucial in order to spread the message across this bare planet. They would be distributed by water and wind.

Spores are also involved in setting up the relationship between roots and fungi. How do fungal spores travel to reach the roots? What are the mechanisms underground? Perhaps some of those arthropods running round helped. From woodlice scuttling along, slugs slugging it out, springtails springing, and mites doing their mighty thing this army on the move could move spores. There were no high fliers, just movers and shakers. We have seen that springtails can detect bacterial spores, but that is for food. Could the larger fungal spores be carried? When the fungal spores landed and grew into the roots, they would grow hyphae which expand what roots could do.

As peds arrive, so do spaces beteen them - pores. These provide a new - albeit small, environment for creatures to live in. In this new world, there are lots if new questions:

How is microbial dispersal influenced by the pore spaces being filled with air, water, or nutrient medium? 

How does pore space geometry affect microbial dispersal, such as channels angled in zigzag patterns, forcing the microbes to navigate through increasingly sharper turns? 

Are bacteria and protists influenced in their dispersal capabilities to new pore spaces by the presence of a fungal hypha? 

How does drying and rewetting soil, and the moving and growing microorganisms, affect the spatial arrangement of the chips’ pore space? 

To answer these questions, electronic chips have been made to replicate the pores. "Both soil microbes and minerals enter the chips, which enables us to investigate diverse community interdependences, such as inter-kingdom and food-web interactions, and feedbacks between microbes and the pore space microstructures.
"Our experiments show that water and nutrient conditions mainly affect water-dwelling organism groups of bacteria and protists, while the shape of the microstructures has an effect on fungal dispersal. Fungal hyphae strongly enhance the colonization success for both bacteria and protists in an initially dry pore space via increased pore wetting. The chips also reveal spatiotemporal changes of microhabitats: hyphae both open up new passages in the pore space system and block them for both organisms and abiotic soil components. Water movements, triggered by drying and rewetting the soil, lead to the development of preferential water pathways that differentiate microhabitats further" (Mafla-Endara et al 2021). 

To have pores, there has to be a structure. "Across the DFS (distributive fluvial system)  there is evidence of plant-sediment interactions in the form of vegetation-induced sedimentary structures, rooting features, and accumulations of plant debris. Plant remains are also found in nearshore facies adjacent to the DFS, attesting to the development of a novel non-marine/marine teleconnection from the production and export of new biological sedimentary particles. The Hangman Sandstone Formation is illustrative of the revolutionary power of cladoxylopsid trees as biogeomorphic agents, forming densely spaced forests and shedding exceptionally abundant plant debris, whilst also impacting local landforms and sediment accumulations and profoundly changing landform resilience against flood disturbance events. These findings provide evidence that the Eifelian Stage (393.3-387.7 Ma) marks the onset of tree-driven changes to physical environments that would forever change Earth's non-marine landscapes and biosphere...The debris thus appears to be a passive accumulation of shed woody material of uniform taxonomy of the former sediment substrate, with limited interaction with classic sedimentary particles and having nit experienced orientation of flowing water. ". Davies 2024 

"Clastic sediments are predominantly clay minerals and quartz particles, with minor amounts of Feldspars, micas, and heavy minerals. Porosity results from the space between the grain particles that is not filled with cement or clay. Porosity is usually in the range from 10% to 30% depending on the grain sizes, compaction, and the amount of cement present between the pores. Permeability, which is the property that permits fluid to flow through the pores, is controlled by the amount of cement, the degree of compaction, and the magnitude and variation of grain sizes." Aminzadeh 2013 

We now know the litter layer has been here for that time. When I say ‘litter layer’ than can be quite thick. It could include peat like substances. You could imagine mosses on peat – much like sphagnum moss on peatbogs today. Basically the ‘soil’ then is the equivalent of what we now call Horizon O. That litter and plant cover would start to protect what is going beneath. Many other developments of soil must have happened below that litter – without affecting it. Which is handy, as it means we can look at what a litter layer or peatbog is doing now, to predict back to earlier times.

This thin skin of litter is what starts to makes lumps of life, not sand, silt or clay. It is a magical mix of minerals and matter, created by life forces. This is the stable environment, that survives extremes, even mass extinctions, to protect soil development below.