Short Story of Soil

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Soil since Civilisation New Science Soil Science Seeing Soil

Short Soil Story

Have you ever wondered how did soil got here? Somehow a mixture of land, air and water? But how? It did not arrive by lorry, so must have built itself. If you believe that soil is a living entity it will have grown. And being a natural body, it must have evolved. Like the rest of life that would have been over many millions of years.

This is the first time that the evolution of soil has been spelled out in any detail. It is not easy trying to work out how soil evolved, as it rarely leaves a fossil (palaeosol) and has often been destroyed - by drowning, ice and volcanoes, but survived several 'extinctions'.

Here we try and see soil as a whole - how it functions along with the key characters and components interacting with each. There are the lumps of soils (peds) with their pores which house myriads of microbes providing food for larger creatures but still minute by animal standards. They help the plants grow that come back to earth to feed more organisms that recycle nutrients making the world go round.
That did not happen overnight; it took about 500 million years....

These hardy beasts, tardigrades, have been around for 500 million years, and are found in moss to this day

Snapshot of how soil got here

If we knew more about soil evolution perhaps we would treat our soil bettter
There were nitrifying and phosphate solubising bacteria over 500 mya, but many more processes have evolved since then. One main soil functions - the decomposition of plant and animal debris into nutrients, came about about in at least these waves, separated from each other by a hundred million years. There were nitrifying and phosphate solubising bacteria over 500 mya, but many more processes have evolved since then. One main soil functions - the decomposition of plant and animal debris into nutrients, came about about in at least these waves, separated from each other by a hundred million years. The first signs of soil probably came from mosses between 500-400mya. The first major soil processes, about 400-300mya were to do with roots, fungi and springtails transferring a substance that was only discovered in the 1990s and called glomalin. We are learning all the time about this substance and here I postulate it helps drive soil metabolism thanks to a process I call 'Glomalisation'. The first early signs of soil came about 50 million years later.

The next wave of decomposition - de-lignification by white rot fungi of dead wood - was between 300-250mya. Then soil took a long time to recover from the worst ever extinction and relied on its existing inhabitants to going on and support the development of lusher vegetation.

We hear a lot about dinosaurs but they needed vegetation which needed soil - and strong enough to withstand their footfall. There was much more of the decomposition we are used to - humification, thanks to the new arrivals - earthworms. Existing oribatid mites also adapted to a chewing and pooing life that produced humus, and humic substances that helped glue soil particles together.

Darwin talked about the rapid rise flowering plants and wondered how it happened. I think the answer lies in the soil. The flowers could be pollinated by insects which were able to fly thanks to having a new stage of growth - larvae in soil. And it was to be another hundred million years or more before we see nitrifying bacterial nodules inside plants; somehow they evolved from both soil dwelling nitrifying bacteria and mycorrhizal fungi that had been around for hundreds of millions of years. After the dinosaurs died out, the great grass prairies, with their fibrous roots flourished, with many birds eating the larvae of insects now finding a home in the soil.

500mya

There was no soil for the first 4000 million years of this planet till about 500mya. There would have been biofilms and bacteria like Azotobacter. Nor was there much in the next 100 million, although some mosses gathered on non-rolling stones. When they clumped together they housed some v small creatures like mites and springtails and unsegmented worms called nematodes. The springtails may well have arrived on films of water as they sprang along following their food, bacteria, emitting the universal 'earth smell'.

Click for Springtail springing

Click to see young tardigrade riding nematode

The soil process of mineralisation had evolved

400 mya

Over the next 50 million years (Late Devonian) the roots of mosses caught particles of weathered rocks. like sand silt or clay. Fungi grew in the moist infrastructure and their growth in the roots of plants provided one of the most important soil processes, called mycorrhiza. The fungi fed nutrients to the roots and in return the plants provided the energy. That energy was released from the fungi in the form of globulin, which now accounts for over a quarter of the carbon in many soils. The springtails fed on the globulin and pooed out soil proteins that helped stick the bits of root & particles together and make microaggregates. Some fungi and bacteria could extract minerals (like nitrates and phosphates) from organic matter, enabling early nutrient recycling. Together, they make the first signs of soil - the crumbly structure that distinguishes it. How soil crumbles is the first test of its quality.

Early - endomorph - springtail

Glomalin on mycorrhiza

The important soil process, I call glomalisation, had been established as a result of mycorrhiza and would help some aggregation

360mya

In the period we know as Carboniferous, most people are looking for coal, while we're looking for signs of 'early soils'. Great mud flats covered the Northern hemisphere to be followed by swamps that made coal. At the edges of the mudflats, four distinct early soils evolved, one on the levees, one around ponds, another in mudflats and another in swamp zones not completely waterlogged. According to the Royal Society graphic (right), this is the start of 'developed soil'. I believe it is when clay particles stopped being movable mud and mixed more with organic debris to create increasingly stable soil structures.Th

The existing mycorrhiza would provide better soil structure, particularly pores, for more creatures to run around, like springtails. They evolved into poduromorphs (right) which were adapting to darker conditions in the newly formed pores, by loosing their springtail, eyes and pigmentation. 'Moss mites', or 'lower oribatids', would also be finding more places to live, and enchytraeid worms (white unsegmented wiggly ones) would have dominated in the peat bogs, just as they do today. There was also a plethora of surface creatures by now including spiders, scorpions, and cockroaches, some feeding on small soil creatures.

Enchytraeid worms

Poduromorph

Lower oribatid

With clay particles and detritus interacting more the soil process of micro-aggregation becomes established

300 mya

Following on, between 300-250mya (Permian), trees grew very well and now on drier land. Many produced tap roots which could grow down and crack rocks to make crevices for creatures. The ability to break down their dead wood, the process of de-lignification became widespread due to the action of white rot fungi. This was the 2nd wave of decomposition and led to the improvement of carbon cycling. The recycling rate of the plant litter within the muchly forested habitat showed up in fossil soils of that time.

Some carbon went back to air, but other, bound in the detritus, provided food for other creatures. When we talk about 'soil carbon' we should remember much of it is running round in the dark. Here we see the first signs of beetles feeding on the degraded dead wood, and they provide the ancestors of modern insects.

White Rot Fungi

Early beetle

The fungi and beetles help add the second wave of decomposition - de-ligniification

250mya

This period of great growth was bought to an end by the greatest 'extinction' called EPE. We have to work out the consequences of these volcanic eruptions and their consequences impacted on soil.

Soil somehow recovered during the following Triassic Period 250 -200 Some soil must have been destroyed but some must have survived to provide habitats for all those 'living fossils' - creatures looking like their predecessors several hundred million years ago.

It seems that much of the earth surface could have been covered in a crust, and that it is this period when lichens come into their own - not earlier as many people believe. They weather rocks but do not produce soil, I would like to know the interaction between lichens and any soil crust. The resurrection took time yet soil survived. The dead wood was probably getting mixed with other particles to make more soil.

lichens

fly larva

There was now enough soil for beetle and fly larvae to live which introduced a giant step in insect evolution where adults could take off.

200mya

While most people associate Jurassic with dinosaurs, we looking at wheat they were treading on. Only now do earthworms, the great soil engineers, and 'higher' oribatids, the 'denizens of the dirt' make an appearance. Why now? It would seem to have a lot to do with their ability to decompose, to chew detritus and through the process of humification and fermentation. Their poo helped further aggregation and the soil to turn browner. How did the earthworms arrive - possibly as enchytraeids from existing soils, as they were endogeic - deep horizontal burrowers. The 'higher oribatids' evolved from lower oribatids, running round 100 million years earlier. They show all the signs of living off lignin in debris, resulting in their own colouration turning brown. Podzols emerged, these are soil types with very distinct horizons,

A new variety of mycorrhiza evolved first in this period called Ectomycorrhiza (EcM). This evolved in plants nearly 20X times (including oaks, beeches birches and oaks around 50mya) and the fungi ca 80 X later . They opened up the rhizosphere and also helped to develop macro-aggregates. These bigger peds enabled bigger pore spaces so the soil could go deeper, water retention was better and the chanels meant air could move along too so the creatures could live deeper.

Macroaggregate

Wireworm (click beetle larva)

The third of decomposition, humification, the ability to break down detritus and recycle nutrients and make bigger aggregates.

150 mya

During the Cretaceous period between 145 - 66mya flowering plants spread 'rapidly' (in geological terms). It was an ‘abominable mystery’ to Charles Darwin as to how they spread so rapidly and widely. Here we lay out several possible explanations, but I believe - to quote an old comedy character, - ‘the answer lies in the soil’. By looking at the soil evolution, with insect, mite and worm evolution, it opens the possibilities of how flowers got pollinated and the new tender flowering plants were consumed, fuelling more soil growth. In particular, and quite ironic when we think of Darwin’s great interest in earthworms, it may well be them that were responsible for dispersing the flowers' seeds through soil.

The third large springtail group - sminthurids- made an appearance. making use of the new tender leaf litter and their fungi

The reach of worms themselves during this period extended from deep horizontal burrows to surface dwelling and vertical digging versions (Anecic). The other key characters were oribatid mites - higher forms - who got into the small nooks and crannies, but also transformed into other forms changing their eating habits and hitching rides on other creatures.

100mya

The Russian scientist Ghilarov demonstrated that it takes millions of years to adapt from water to land, and insects did that in soil. In this period, they really took off. But in order to do that many spend many years in the soil as larvae, before taking to the air as adults and helping pollinate the flowers. Higher oribatid mites were now chewing and pooing their way through a lot of soil, and a group of mites called Astigmatids evolved further by hitching rides on other soil creatures.

While woodlice look ancient, there is no previous fossil evidence. It may be now that one of the few true terrestrialisations - going from water to land - occurred. There was now enough moist ground for them to move into without long term adaptations.

Woodlouse with young

There was also the appearance of nitrogen-fixing nodules on certain groups of plants - called legumes. It took till this period for this evolution of N-fixing bacteria to work with roots, and this may well be related with mycorrhiza. Two new forms of mycorrhiza also appeared. But how and why the N-F Bacteria, legume roots and fungi come together in this relatively late period, is the holy grail of many agricultural scientists, as it could solve some of the problems with nitrogen fertiliser use.

N-nodules appear in this period

Now all the soil processes, and most creatures, we know soil today were present. But then came the extinction that killed off most dinosaurs.

66mya to now

During this Cenozoic Era, the soil - once again - survived an 'extinction' and helped rebuild life on the planet. As the continents spread out some of the previous soil inhabitants evolved somewhat differently on the different continents - oribatids and earthworms evolved separately.
After the dinosaurs departed a new soil biome - under grassland - built up. Many of its habitants had been around for millions of years and moved in from elsewhere. These included earthworms and roundworms, along with the mites and springtails. There were some new insect larvae eating the grass roots, which are doing the same today and being pests. New insects that fed on the increasing number of smaller soil arthropods. As all their numbers grew, so did their predators, particularly the dinosaur descendants - birds, and newly emerging small burrowing mammals.

Other mammals, the herbivores, took to the grass forming a very important symbiosis that keeps the planet cool to this day. But for the symbiosis to work, the soil-dwelling dung beetles and eathworms recycled the nutrients via their poo to make it work.

This is the first time this level of feeding could occur - birds eating earthworms

and insect larvae (wireworms)

Some of you may think that this story has been around for ages. I have been waiting 50 years so decided to do it myself. Nobody has covered the ground like this before and it should throw light on many biological debates, both below and above ground.

Green links = internal, blue = external, brackets = academic reference

The events here are all verifiable from reputable, referenced, sources, the first time they have been put together like this. See New Science of Soil While based on peer-approved academic papers, it is a new way of seeing soil. There are many competing versions of several of these soil-related events and how they fit together. Hopefully this stimulates more debate.

When deciding on whether these events are true, we need to ask whether it each is possible, and plausible and then how is it provable. If you choose to dismiss, then you have to ask: 'how, when and where did that particular part of earth emerge, and does it fit with what we already know? Let's look at the challenge that faces us

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