Embedded Files
Shear said in his important review: "The first terrestrial ecosystems are now thought to have been based on plants of a moss-like grade of organization, mats of algae, and crusts of lichens and cyanobacteria" (Shear, 1991) This was pretty well accepted in the latter part of the last century as the main route to 'terrestrialisation'. But let's look closer at each of these candidates for early soil evolution.
Fungi
Fungi
Fungi used to be classed as plants, as they have a cell wall with chitin, but as they have no chlorophyll they were given a kingdom of their own from around 1960 onwards.
“Microfossils which represent the remains of the imperfect stages of terrestrial Ascomycetes, provide evidence for an origin of this group at least contemporaneous with the earliest land plants.” (Sherwood and Gray, 1985).
The defining feature of this common modern fungal group is the "ascus" ('sac'), in which nonmotile spores, called ascospores, are formed. But how do ‘nonmotile’ spores move? Springtails perhaps?
Prototaxites
Prototaxites
Prototaxites was a giant fungus and one of the weirdest organisms to ever inhabit this earth. Often over 8 meters high and a metre wide they would have stood out from the rest of the vegetation. They were first thought to be a conifer (hence ‘taxus’ = yew) but – after 150 years of wrangling - it is generally thought to be a fungus – one which is spore bearing (Honegger et al., 2017). They have disappeared by the end of the next period we explore.
Perhaps their long-lasting contribution to life on land is “the suggestion that sedimentary deposits of cyanobacterial or algal-derived organic matter from ephemeral water bodies were probably important substrates for the subterranean hyphal network of Prototaxites (Hobbie and Boyce, 2010). Could there be a connection between the demise of Protoaxites and the evolution of trees – using soil-dwelling fungal symbionts absorbing nutrients for the trees - as we’ll see later?
“Prototaxites lived between 420 million and 350 million years ago, at a time when millipedes were among the first creatures to make their home on dry land”
Role millipedes play
AMF
AMF
Increasingly we are finding that arbuscular mycorrhizal fungi (AMF), which we will hear much more about in the next period, are associated with bryophytes (below). “There are 55 new AMF taxa that are apparently unique early-diverging land plants (liverworts, hornworts, lycopods, and ferns).... We show every order of arbuscular mycorrhizal fungi colonizes early-diverging liverworts, with non-Glomeraceae being at least 10 times more common than in flowering plants. Arbuscular mycorrhizal fungi in liverworts were delimited into 43 novel sorts specific to liverworts. The discovery that early plant lineages are colonized by early-diverging fungi supports the hypothesis that arbuscular mycorrhizal are an ancestral symbiosis for all land plants". (Rimington et al., 2018) We will see also that they play a key role in the development of several key soil functions.
Lichens
Lichens
The oldest certain lichen fossil is from the Rhynie chert over 400mya. Lichen is a symbiotic relation between a fungus and an algae. They come in all sorts of combinations. There is a widely held view that lichens, covered the landscape earlier on. The fungal half of lichens are the drilling specialists, excreting acids that break down rock and enable the fungus to get a hold in micro-trenches, cracks, and small lens-shaped cavities formed by water. The acids are derived from the food that the algae provide to the fungus. Together they are found all over clinging to rocks.
Lichens grows on lots of rocks all over the world, causing ‘weathering’ - ie rock breakdown. Since the fungus can protect its algae, these normally water-requiring organisms can now live in dry, sunny climates without dying, until next rain or flooding, while storing food for the next drought period. The helpful habits of the algae capturing food and the fungi mining rocks for minerals provided a great vehicle to explain how the land may have been ‘conquered’, leaving behind organic matter for others to follow. The lichen-based communities would have - in the absence of disturbance - set up a positive feedback loop in which increased biological activity would have made the site even more suitable for life.
Do lichens create conditions for soil development? Soil is much more than weathered rock. There are unique soil structures, based on 'peds'- and pores. I believe moss (below) is a more likely plant candidate to kick off soil formation, as you can see here, lichens didn really have an impact for
Later...
Later...
“Lichen‐like associations are recognized as a component of early terrestrial ecosystems, although apparently with a limited abundance…Some of these were very simple and possibly they represent loose consortia of fungi and cyanobacteria rather than a proper mutualism. Earlier records of fossils assigned to the lichens lack credibility because details of anatomical structure are absent and they are plausibly interpreted as a variety of other things, ranging from inorganic sedimentary features to biofilms or early metazoans.” (Strullu-Derrien et al., 2018)
“They’re not as old as once thought. Contrary to conventional wisdom that lichens were some of the earliest arrivals on land, a study published in Geobiology adds to the case that lichens most likely made their way to land some 100 million years after vascular plants, such as ferns.”
From the Geobiology study: “Their poor preservation potential and the classification of ambiguous fossils as lichens or other fungal–algal associations have further reinforced this view. As unambiguous fossil data are lacking to demonstrate the presence of lichens prior to vascular plants, we utilize an alternate approach to assess their historic presence in early terrestrial ecosystems. Here, we analyse new time-calibrated phylogenies of ascomycete fungi and chlorophytan algae, that intensively sample lineages with lichen symbionts. Age estimates for several interacting clades show broad congruence and demonstrate that fungal origins of lichenization postdate the earliest tracheophytes” (Nelson et al., 2019). i.e. lichens followed ferns, not the other way round.
The study “determined that lichen-forming fungi first evolved about 250 million years ago, on average — long after those (vascular) plants were rooted on land. The timing varies though, suggesting that different fungi developed their algae-hugging habits independently, and didn’t inherit it from one main ancestor.”
Which of course raises a greater question. If lichens were not in at the start, what was? It certainly makes us think. Lichens can etch themselves in rock and may leave some organic matter around. But that offers little protection to other organisms. So what is the origin of soil? What other organisms were involved?
Known only from the Rhynie chert (410mya) is a group of plants known as nematophytes, whose bodies consisted of clusters of banded and smooth tubes. They seem to have been diverse, including the largest land organisms of their time with trunk-like structures up to a metre in diameter. They must have been components of early land communities and may be the first plants to make lignin-like compounds. However, the lack of a clear definition of the nematophytes has led to it being used as a ‘wastebasket taxon’
Bryophytes
Bryophytes
There were signs of the first ‘land’ plants – mosses and liverworts – over 400mya. Growing in and out of water, using light energy to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds. Bryophytes include moss, hornworts and liverworts and first appeared around 450mya
More
More
They could all grow hugging water lines, but did not have distinct roots, nor leaves or stem. They do not have their own internal water-holding (vascular) structures. You could think of them as creating thicker, more luscious carpets. Although there were alga, fungi, bacteria and other bugs that were about, together they did not make soil.
Let’s have a look at these bryophytes in more depth – as they would be around, whenever soils were formed. They would all be used to living in damp conditions, but with periods of time when it was dry or hot, when each found different ways to survive
Origin
Origin
“The origin of bryophytes during the upper Ordovician period (around 450mya) represents a notable event in the evolution of life, leading to the diversification of terrestrial organisms. From a mating systems perspective, the evolution of bryophytes resulted in sexual reproduction partially escaping the aquatic environment (Rosenthiel et al., 2020), as we’ll soon see in the mosses.
Liver & hornworts
Liver & hornworts
Liverworts are named after the shape of their ‘leaves’ - only they are not 'real leaves' – like a liver. Hornworts refer to elongated horn-like structure, which is the spore bearing part. Many liverworts are tolerant of repeated cycles of wetting and drying and this makes them particularly successful
More
More
Liverworts may have been around at this time, but they did not diverge (ie spread out) until several hundred million years later (Cooper et al., 2012)
This raises the issue throughout evolutionary biology that we may be able to point to the ‘ancestor’ but that tells us little about when the characters ‘radiate’ and ‘diversify’ impacting on the world much more.
Mosses
Mosses
Mosses, liverworts and hornworts are not all that closely related, being united only by sharing their peculiar life-cycle. Moss clumps make carpets found just about anywhere you choose to look. These mosses housed tardigrades and nematodes, probably the Earth's most persistant occupiers.
Carpet
Carpet
Tim Lenton, Prof of Earth Sciences at Exeter says: “What we are seeing are the first true plants – mosses, liverworts, bryophytes - entering what was previously Matworld. You could think of them as creating thicker, more luscious carpets…Once you have established Mossworld, you have a food source. You’d expect animal evolution to take advantage.”
Mosses are very resilient to all sorts of conditions and are found all over the world, mostly in moist conditions, but hanging on in dry conditions only to come back to life. They can reproduce from simple vegetation parts. They need only air and water for nutrients to survive, not soil. Perhaps that is the big clue to their role. Looking through a roof moss sample today gives an insight as to what may have been going on then. Clumps of moss roll down making bigger clumps that block my guttering. A sort of black silt forms that clogs up my homemade water collection system. Is that what happened all those years ago, with moss growing on rocks, rolling down and and clumping together to provide barrier to collect more and start making soil. In side a moss clump we find up roundworms, mites springtails, and those water bears.
Their living conditions creates the conditions for soil to form. Part of my soil evolution theory is my that mosses conquer the conditions and provides the silt from which characters in the moss create soil.
Moss clump showing with dead, un-decomposed, matter & fungal filaments, that could make basis for living environment - and ultimately soil.
It is commonly accepted by most botanists that mosses evolved from a simpler filamentous green alga. As the seas went up and down, they could have left filaments of algae on the rocks, some of which survived. Just a piece of moss can grown and replicate. "There is no evidence of mycorrhizal-like associations in mosses, likely due to their unique fungal-like multicellular rhizoids removing the need for symbiosis" (Rimington et al., 2018)
The earliest evidence of the presence of mosses on Earth dates back to around 460mya, during the Ordovician period. Rocks dug up when building the Douglas Dam in Tennesse, were found to host a ‘benchmark assemblage of early plants and fungi’ (Retallack 2019) This study may show that the Cambrian Explosion went beyond marine life but also includes first plant life ‘on land’..
Early moss - Takakia
She also has an Appalachian lichen named after her Japewiella dollypartoniana
“One of the newly identified fossil moss species, Dollyphyton boucotii, has been named for legendary singer Dolly Parton, whose Dollywood theme park is located a few miles away from the original rock deposit.” Dollyphyton has broad leaves like those of the living peat moss Flatbergium, considered the group to give rise to the large group present day mosses, Sphagnales (Shaw et al., 2010).
Funny names
Funny names
Talking about naming organisms, there is no international body - like for geological time periods - to control the nomeclature of classification of creatures. Instead there is just a series of recommendations laid out by the International Commission on Zoological Nomenclature. Curiously this new moss name reminds me of another ‘Dolly’ name, this time of a true bug. “British entomologist George Willis Kirkaldy gave a series of true bugs the suffix -chisme, meaning "news" but pronounced "kiss me". Starting with polychisme (Polly kiss me), he went on to name dolichisme (Dolly kiss me), ochisme (Oh kiss me), and many more, seemingly after his romantic conquests. Kirkaldy was post-humorously criticised for frivolity by the London Zoological Society in 1912”.
On rooves
On rooves
The organisms that gave the Earth its first breath of fresh, clean air and made life possible were mosses. Like lichens they produce acids that can weather rocks, producing cracking. But they do much more in terms of creating new conditions. The drama unfolded over 450 million years ago and went on for tens of millions of years. There are no surviving witnesses, but it may be very much the same now as all those years ago. We also need the testimony of fossils and molecules, along with computer models of the few spores preserved in ancient sediments.
Moss growing on roof tiles shows what may happen on bare rocks.
Static stones gather moss
Static stones gather moss
We can see in present-day conditions what may have been going on for hundreds of millions of years - on your roof. We seem to gather moss whatever we do. After a while those clumps fall off the roof, either clogging you guttering or dropping to the ground below. In so doing, they mix with other clumps to produce a ball of roots and leaves - but also a whole new growing environment.
Using present-day properties to help work out what went on in the past also extends to its inhabitants. Their structure creates an environment that harbours creatures like tardigrades, nematodes and protists which lived in the water film of the plants, while also hosting air breathing springtails. Nematodes, oribatids and springtails are the three most dominant animal groups in soil all over the world today. These all exist in mosses today in what may have been their ancestral forms from over 450 mya. All of the groups have means to withstand a wide range of circumstances, both wet and dry, cold and warm - just like moss
Loose moss could gather in lumps in a gullley
Moss breakdown
Moss breakdown
The primary decomposers of moss are microorganisms like bacteria and fungi., which would have been around for millions of years before These organisms secrete enzymes that break down complex organic molecules in the dead moss into simpler compounds.
Carbohydrates (like cellulose in the moss cell walls) are broken down into sugars.
Proteins decompose into amino acids, and eventually into simpler nitrogen-containing compounds like ammonia.
Lipids are broken down into fatty acids and glycerol.
This process produces carbon dioxide (CO₂), water (H₂O), and energy, which the microorganisms use for their own growth.
Proto Soils
Proto Soils
The accumulation of debris from these early plants provided the beginnings of soils when they mixed with other minerals, including clay, lying about.
Cryptogamic ground covers (CGCs), comprising assemblages of bryophytes (hornworts, liverworts, mosses), fungi, bacteria, lichens and algae, indicate that mosses make deeper surface layers than hornworts. "(up to ~ 7 cm), structurally more complex, and more organic-rich. We term these thin layers and profiles proto-soils....The evolution of more complex soils through the Palaeozoic (540-250mya) may have been driven by a shift in body plan of CGC-like organisms from flattened and appressed to upright and leafy." (Mitchell et al 2021)
Reaction with clay
Reaction with clay
There is a massive area of science dealing with the reaction of clays and organic compounds, much of it new. This will throw light on the sort of interactions going on 4-500mya when clays met cellulose, amino acids and glycerol.
"The concentrations of carbohydrates increased when the clay contents of soils increased from 0 to 5 and 10%, respectively, showing that the clay contents influence the capacity of soils for stabilization of carbohydrate" Rakhsh & Golchin 2018
"Basic (+ charged) amino acids were strongly adsorbed by two clay minerals. Neutral (uncharged) amino acids were taken up appreciably by montmorillonite, but little if any by kaolinite. Acidic (- charged) amino acids were adsorbed only by kaolinite. These appear to be related to electrostatic interactions." (Hedges & hare 1987)
Today
Today
Mosses do not just grow in lawns, but their 12,000 species are found all over the world in all sorts of conditions.
Racomitrium moss (right) grows on larva in Iceland and is 250 years old and can be 20-30cm deep
Moss in Antarctica goes further still. It can be several metres deep. Their survival properties are remarkable."Recent field observations of new moss growth on the surface of small moss clumps re-exposed from a cold-based glacier after about 400 years of ice cover have been accompanied by regeneration in culture from homogenised material"
" When they began to see the 1,500-year-old mosses start to regrow, it came as a real surprise." And not just to them. Imagine the impact on the environment of moss that can live this long providing a stable NEW environment.
BBC 'The Magical world of moss
This excellent programme missed out at the end when looking into the possibility of moss growing on Mars, rather than reducing desertification (link to anthropocene) ). Classic habit of looking at stars rather than soil for answers.
We can see today what may have gone on 400+mya. The Antarctic's moss ecosystems "are pivotal in terms of changes in the spatial extent of vegetated ground cover18, organic soil formation19 and higher plant colonisation20. The vertical accumulation of moss bank systems has tracked the long-term trend in multi-decadal warming in the region21,22,23, but major questions remain over the existence, continuity and controls on lateral spread of moss-dominated systems". Roland et al 2024
Sex
Sex
Mosses have a fascinating reproductive life cycle known as ‘alternation of generations’, which contributes to their ability to spread and adapt. The sexual phase, called the gametophyte generation, produces gametes, or sex cells, and the asexual phase, or sporophyte generation, produces spores asexually. Mosses sexual reproduction requires free-motile sperm to ‘swim’ with the aid of water across the terrestrial landscape to fertile females, a reminder of its aquatic origins.
There is evidence of mosses emitting scents, similar to those between flowering plants and insects, that moss-dwelling microarthropods are attracted to. "Our results indicate the presence of a scent-based ‘plant–pollinator-like’ relationship that has evolved between two of Earth’s most ancient terrestrial lineages, mosses and microarthropods. The model of ‘swimming sperm’ has led to the general view that sperm dispersal among bryophytes is quite limited, with most fertilization occurring within about 10 cm. However, recent research using the moss Bryum argenteum shows that moss sperm can be dispersed by microarthropods, specifically springtails and oribatid mite” (Rosenstiel, 2012, who we will come across shortly. Springtails could well have been spreading moss sperm around over 400mya.”
These primitive, low-growing mosses drew down carbon from the air, created some topsoil for later vascular plants, and in 50 million years or so reduced carbon dioxide and increased oxygen in the atmosphere to levels that endure today. These plants increased atmospheric oxygen to present levels by 400 Mya (Lenton et al., 2016) The presence of mosses this early may “demonstrated acceleration of chemical weathering that may have fuelled the Great Ordovician Biodiversification Event (GOBE)” (Harper, Zhan, and Jin, 2015)
As a scientific sleuth, you know that just because somebody has an hypothesis, does not mean it is true. You can check the moss or lichen hypothesis as we progress.
Mosses are my main contender for soil creation. They are clearly very widespread if they could affect the world climate as they did. They can grow over hundreds of years on rocks, and survive for even longer under frozen conditions. Their growth provides a thick matt of living matter that provides and protects a layer of organic debris, where creatures could live and evolve over tens of millions of years.
Page updated
Google Sites
Report abuse