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My friends
My friends
It is curious that others have not asked the same question: 'How did that soil get here?' Most people take it that soil has always been there.
When we ask people interested in soil, how they think soil came to be here, they come up with a mixture of things
Some say something about mixing and mashing over millions of years. They think minerals and debris were mixing up and mashed, like potato, into some sorts of clods. That is because we only see soil as brown lumps.
Quite a few people feel it has been washed down from the hills and collected round river beds. The mountains erode and the debris is washed off the hills. But that would be sand, silt, mud and clay - not a structured living complex or soil civilisation. Clearly moving water has something to do with it, but ‘washing’ or 'weathering' does not explain the soil structure.
One soil scientist friend of mine said he had just presumed there were pores in the debris of rock breakdown, and life lived in these. But it doesn’t take a moment to realise that pores between particles of rocks, sand and silt only provide a house until the next storm comes along. It is the soil - the aggregates and pores - that provides the stability of the structure and space for survival.
Scientists
Scientists
Somehow the soil has moved here by many organisms and processes. Right under our feet, it somehow got here. It could not have dropped from the sky. So which way did to come?
Darwin explained evolution, but not that of the soil. Did he think it was static too?
Evolutionary biologists should know better, but most also take its formation for granted. However, there is some mentions.
Montgomery in Dirt:Erosion of Civilisation has a go, saying soils probably developed when rivers flooded and the silt was spread over the rocks. He predicts a time of “a suite of adaptations necessary for survival in harsh terrestrial environments.”
In 'Early evolutionary stages of soil ecosystems": “Worms and arthropods emerged onto the land and into inland water reservoirs in the Cambrian period; they mixed organic matter with mineral earth and thus enhanced the soil-forming process. Modern soils were formed in the Devonian period after the dispersal of higher plants, which replaced the mats from shallow waters.” Ponomarenko 2015
Just like that! I think there is a lot more to it than that. After all what is 'the soil-forming process'? Did soil form once or many times?.
Co-evolution of soil & plants
Co-evolution of soil & plants
“One of the most significant outcomes of biological evolution has been the co-evolution of soil and terrestrial ecosystems. This co-evolution was initiated during the Devonian era, approximately 350mya. Plants spread across upland continental regions during the explosion of life that led directly to today’s soil. During the Devonian, the early forest ecosystems became complex, containing large seed-bearing trees that were deeply rooted. As ecosystems affected and were affected by an increasing depth and volume of soil, respiration from roots and microbes increased the concentration of Carbon dioxide in soil atmospheres, weathering underground rocks via carbonic acid dissolution and releasing nutrients for subsequent root and microbial uptake. “ (Richter et al 1995). We want to know more about 'led directly to today’s soil'
The British Natural History Museum has examined early soils to try and understand how "first soils co-evolved with biological components such as fungi and plants. Coevolution may have occurred with chemical signalling and micro-organisms (Blouin 2018), while Occhipinti (2013) sees coevolution - a tight ecological interaction between two or more species - where soil animals are the plants' 'enemies'. terHorst & Zee 2016 examined the potential for eco–evolutionary dynamics in plant–soil feedbacks (PSFs).
Japanese version
Japanese version
Fujii Kazumichi "a unique soil researcher who won the Kawai Hayao Award" wrote "the amazing history of soil and humanity" and spells out "500 million years of coevolution of organisms and the soil. Plants give rise to soil and soil nurtures plants and animals".
But only those animals above ground it would seem! Where are the worms, larvae, springtails and mites?
Thanks to Kaede for translation and find!
Lichens
Lichens
The Earth ’ TV series hosted by Chris Packham, cite ‘lichens’ as the first possible soil. This programme set out to show "how plant life turned the Earth from a barren rock into a vibrant green world" The only mention of the role of soil in this programme is about lichens at this point in time.
Dear Chris P,
Could you persuade the Beeb to make a final Episode 6 on 'How Soil made our Earth'. You could use this site to do so. There is another 450 million years of soil evolution after your lichens.
Cheers Charlie
If none of the above explain how soil came to be under our feet - if soil did not drop down, get mixed and mashed, was not mined in a rock somewhere or get blown along or be washed down, then where did it come from? It must have come from somewhere, and then somewhere before that. Has it evolved more or less where it is now? Underneath our feet. But how could that happen all over the world - producing remarkably similar stuff?
You may see 'soil evolution’ referring to pedogenesis, which takes hundreds of years But here we refer to hundreds or thousands of years, whereas here we are talking about what would have been millions of years to bring the various parts and processes together in the making of soils
I spent three years doing my PhD looking down a binocular microscope counting and identifying half a million small soil creatures. I realised that most were ‘primitive’ forms in terms of evolutionary development, so most of the soil evolved BEFORE advanced forms, like insects. More advanced forms of creatures are there, but infrequent and often don't fit within the small-pore soil structures. There are some insect larvae and occasional they can become pests, but usually soils are dominated by smaller more primitive arthropods like springtails and mites. So I kept asking myself – why is that? When did these small soil animals inhabit the soil, and did they help form that soil civilisation. That was 50 years ago, and I kept waiting for somebody else to have a go at working out soil evolution, Despite lots of discoveries in the ensuing time, there is no overall theory as to how soil came about. So I feel it is time for me to have a go.
Throughout the evolution of soil, we have to remember that good old law – the second one of thermodynamics. It says that all matter tends towards disintegration – towards a high entropy. There we can easily move things around to maintain shape – like a mound of sand. A low entropy – as found in soil – cannot be easily around to maintain the same shape. It means energy must have gone into the system at all stages to counteract the move towards high entropy and disintegration. How does soil manage to get that energy over millions of years? The energy going into the soil must come from somewhere and be maintained somehow, now as metabolic processes.
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