A planet of lichens. Photograph by E. Roe.
Falling in love is what happens at Schumacher College. Satish says, “You come here to study…but you also come here to fall in love”.
Fall in love with the Earth: feel your body burn like a furnace as you imbibe her magic airpotion, and cast aside your sense of separate self as she entwines her heart with yours. She is Gaia who brings forth the world from herself. Our work as human beings is to heal the rift that we have created between us.
This essay is a grain of sand in the mortar that might fill a small gap in the larger rift. I’ve written it for the love of Gaia, because I want you to notice her clear, still eyes peering from crystalline rock, and her delicate tongue testing the quality of the woodland air: these are the lichens, which are Gaia’s sense organs, her medicines, her adornments, and her geological shape-shifters.
Lichens are found in a wide range of habitats, they can live for millennia, and they’ve been around for millions of years. It shouldn’t be surprising, therefore, to discover that they’ve played a significant role in the regulation of our planet’s climate and the evolution of the whole Earth system that is known as Gaia: organisms and their material environment coupled together in a self-regulating system.
Like the fungal hyphae that constitute the structure of the lichen, the relationship between lichens and Gaia provides the main body of this essay, and anchors it in the third module of the M.Sc. in Holistic Science. Splashes of colour come from brief explorations of other aspects of lichen life, which nestle, algal-like, in the tissues of the essay.
Learning about Gaia theory and the symbiotic nature of lichen life has deepened my appreciation of how we are embedded in a world of our own making, in relationship with other beings. In the final section, I reflect more on this.
I begin, however, with a light-hearted scene of lichen love, in which I hold a conversation with an algal cell who is about to become part of a lichen symbiosis
Xanthe: She’s in the Xanthophyta, yellow-green algae, which are occasionally found in lichens.
Asco: He’s a typical lichen fungus, a member of the Ascomycota.
Treb: This is short for Trebouxia, a green alga in the Chlorophyta, commonly found in lichen symbioses.
Hey, Xanthe, who’s that good-looking fungus I saw you dancing with, at the rock concert?
Asco? He’s really fit, isn’t he? You won’t believe it, but he’s asked me to move in with him!
What? After one date?
Well, we’ve been seeing each other for a few weeks, actually, but he wanted to keep it quiet because he already has a partner, a chlorophyte. Treb’s been living with him for years, preparing his food and enjoying the comforts of his home. They’ve even talked about having kids, but I get the impression she hasn’t been interested in sex for a while…
So, that’s where you come in?
I will admit a certain attraction…but I’ll make it clear to Asco that I’m not looking for a permanent relationship. I’m perfectly capable of living on my own and, as long as he accepts that I might move out if it suits me, we should get along just fine. He’s told me that he can’t bear to live alone without an algal partner, but he already has Treb to take care of his daily needs.
Well, I’m a bit worried about you getting involved with Asco, because I heard through the grapevine that, when he first met Treb, he attacked her, and she’s virtually a prisoner; the only way she could survive was to keep feeding him. Are you prepared to do that?
I’ll merge with him on a sunny day, so that I can impress him by photosynthesising enough polysaccharides for both of us, but he’s an expert at digging out tasty mineral snacks from the rocks, so we make a good combination. I think it’s in my best interests: all this talk of global warming and drought is a bit scary; I can’t tolerate drying out for long periods, so I’ll take my chances living with Asco. And I rather like the idea of one of my future cells floating off, wrapped up in a piece of his thallus…it’s not what you’d call sex, but it would take me to new places!
I bet your ancestors were illegal immigrants: your great-grandmother was probably a plastid that asked some unsuspecting prokaryote if she could stay for a few days, and never moved out.
Hey, don’t slander my great-grandmother…call her an endosymbiont, if you must, but parasite she was not!
Relax, Xanthe. We’re all the products of endosymbiosis. Co-operation is the way forward. So, go for it with Asco. Lichens are a crucial part of life on the planet and their influence is felt far and wide. In fact, the earliest lichens may even have triggered a snowball Earth, millions of years ago.
From what I’ve been hearing down at the waterfront, it sounds as though we could do with one of those right now. It seems like even the ocean is warming up.
You’re right about the rising temperatures…but I don’t think lichens can come to the rescue this time. Anyway, let me tell you the wondrous story of lichens and Gaia.
Gaia, in ancient Greek mythology, was the name for Mother Earth. The universe was brought forth from her, so all her children were formed of her substance. As Jules Cashford writes,
In contemporary terms, Gaia was a vision of the universe as one dynamic living whole.3
Aspects of this Gaian view can be found in ancient Greek philosophy as far back as Thales and Pythagoras in the sixth century BCE: these early scientists perceived the Earth as an organism, and their underlying cultural assumption was that the world was alive and intelligent.4
A significant divergence from this view occurred during the seventeenth century in Western Europe, when Cartesian dualism gave rise to the image of Nature as a machine designed by God, and running according to his immutable laws. From this philosophy arose the separation of spirit from body, and humans from Nature, who was no longer seen as a conscious being. This reductionist approach invalidated our direct perception and experience, and led us to consider as matter as dead, and living beings as insentient.
Three hundred years later, reductionism can still anaesthetise us against feeling the pain of the Earth when she is ripped open by gargantuan earth-diggers or poisoned by wastes spewed from our factories. Only when we perceive ourselves as embedded in a sentient world can we begin to love and respect the complexity of the systems which have evolved over billions of years and on which we rely.
The study of the Earth and her systems has become more integrated and holistic in recent decades through the work of James Lovelock, who has brought forth a new awareness of the Earth as a single, evolving, self-regulating system, which he calls ‘Gaia’.
Earlier in the twentieth century, the Russian scientist Vladimir Vernadsky founded the inter-disciplinary field of biogeochemistry, which studies the large-scale cycling of chemical elements through organisms and their environment, but biogeochemical models lack self-regulatory cybernetic feedback loops, which Lovelock emphasises in “The Revenge of Gaia”:
The key to understanding Gaia is to remember that it operates within a set of bounds or constraints. Gaia itself is firmly constrained by feedback from the non-living environment. Darwinists are right to say that selection favours the species that leaves alive the most progeny, but vigorous growth takes place within the constrained space where feedback from the environment allows the emergence of natural self-regulation.5
The original Gaia hypothesis put forward by Lovelock in the 1970s was that living organisms controlled or regulated the systems that supported life on Earth; further research has shown that the whole system evolves and is self-regulating and no single component is in charge. This is the Gaia theory, which is supported by evidence6 that an emergent property of the whole planet is its ability to self-regulate its temperature, pH of surface ocean waters and availability of chemical elements, within limits that life can tolerate, through feedback loops and tightly coupled interactions between the biotic and abiotic spheres. His continued use of ‘Gaia’, rather than ‘Earth system science’ means that we have Gaia as the name of our new – and old – story of the Universe.
Gaia did not begin at the first signs of life: she began when there was enough life on Earth for the first communication between biotic and abiotic to grow into a conversation. As Lovelock reflects, in “Scientists Debate Gaia”, this seems to have happened not long after life began:
Soon after its origin, life was adapting not to the geological world of its birth but to an environment of its own making.7
In other words, the earliest living organisms, which were prokaryotic (non-nucleated) cells brought about changes in their physical environment that made their living conditions more suitable for themselves, whilst evolving in response to changes in that environment.
Lichens enter the story a few billion years later, after a long period of bacterial evolution and the emergence of single-celled eukaryotic organisms. The lichen kind of association formed repeatedly during the course of evolution, but evidence for the earliest forms is in the shallow seas of the Neoproterozoic, about 600 million years ago.
These proto-lichens might have looked somewhat different from modern lichens, but their symbiotic way of life was similar. It’s likely that they were the first colonisers of the land, breaking down bare rock, creating soil, and providing micro-habitats where biodiversity evolved. The significance of lichens’ arrival on land is explored by Tim Lenton and Andrew Watson in their astonishing and informative book, “Revolutions that Made the Earth”8; much of what follows has been taken from this source.
My particular area of interest is their hypothesis of how early lichens liberated phosphorus from rocks, caused a rise in atmospheric oxygen, reduced the level of atmospheric carbon dioxide, and cooled the planet to such an extent that she was plunged into a ‘snowball Earth’ scenario. How could such small and slow-growing creatures affect the global climate to this extent, “upsetting the steady state that had maintained comfortable temperatures throughout the Proterozoic”9?
[Proto-lichens] began to accelerate the weathering of continental rocks, and this would have had two fundamental effects on the atmosphere: increasing oxygen, and reducing carbon dioxide concentrations.10
Most of the Earth’s crust is made of granite, which is a silicate rock. This can broken down physically into small particles, but the rate of weathering is increased greatly by the action of living organisms. Figure 1 shows lichen, mosses and other plants growing on a granite tor, as an example of biologically-assisted silicate weathering.
Fig. 1 Bench Tor, Dartmoor
Lichens are particularly skilled at weathering rock. They do this in several ways: one, by producing lichenic acids which dissolve rock; two, through respiration, producing carbon dioxide and increasing the concentration of carbonic acid in surrounding water; and, three, with the growth of fine fingers of hyphae that reach into tiny cracks in rocks. These hyphae produce polysaccharides which swell when wet, micro-fracturing the rock.
Lenton and Watson found that there was a significant increase in atmospheric oxygen at the same period in geological history as the extensive silicate rock weathering by proto-lichens. An explanation for the rise in oxygen is that an increased amount of phosphorus was released from the rocks by lichen activity: while some stayed on the land, much phosphorus was washed into the ocean. This would have increased the biological productivity of the ocean’s cyanobacteria and algae, increasing photosynthesis and releasing more oxygen.
However, Lenton and Watson point out12 that an overall rise in oxygen occurs because there is increased burial of reduced carbon from atmospheric CO2. Carbon burial increases because, as described above, biological production in the ocean rises; when cyanobacteria and algae die, their carbon-rich bodies are buried in the sediments, and free oxygen is released.
Figure 2 shows this as part of a feedback loop which I’ll complete later (in Figure 4).
Fig. 2 Lichen activity leading to a rise in oxygen levels. Solid arrows indicate direct relationships.
Moving to the next part of the story, decreased levels of carbon dioxide from silicate weathering can be explained as follows:
When granite is weathered, water and carbon dioxide can react with silicate minerals in the rock. This reaction is represented by
CaSiO3 + 2CO2 + H2O = Ca2+ + 2HCO3- + SiO2
silicate mineral + carbon dioxide + water = calcium ion + bicarbonate ion + silica
This story is set in a time long before the origin of coccolithophores, which are exquisite marine organisms that combine the above ions to make their chalky external plates,
[b]ut in the heyday of Gaia’s infancy, some 3,000 million years ago, huge bacterial communities (the stromatolites) laid down vast crusty platforms of limestone13.
This is how Stephan Harding, in his enlightening and heart-filled exploration of Gaian science describes the role of early organisms in the control of calcification of the ocean.
The production of limestone (calcium carbonate) in stromatolites can be shown as
Ca2+ + 2HCO3- = CaCO3 + H2O + CO2
This would have released carbon dioxide…but only one molecule, compared with the two molecules trapped in silicate weathering, so the net effect would still have been a reduction in atmospheric CO2.
Gaia emerges in this picture when we add that the rate of silicate weathering is temperature dependent: it speeds up as the surface temperature goes up, and it slows down as it cools14.
Figure 3 illustrates how atmospheric temperature regulation emerges from these interactions through a negative feedback loop.
Fig. 3 Cybernetic diagram showing an overall negative feedback loop. Solid arrows show direct relationships; dashed arrows show inverse relationships.
When the rate of weathering increases, the level of carbon dioxide decreases. This reduces the greenhouse effect, lowering the atmospheric temperature. This, in turn, reduces the rate of silicate weathering which causes a rise in CO2 levels. The greenhouse effect increases, the temperature rises, which speeds up silicate weathering…and so on.
Imagine the Earth in the Neoproterozoic, 600 million years ago: proto-lichens are clinging to bare granite, their tiny algal eyes looking out into the cosmos, while their fungal hyphae dig in the dark like archaeologists, searching grain by grain for rare phosphorus. Silicate rock weathering increases as the proto-lichens colonise the rocks, decreasing atmospheric CO2 levels and lowering the temperature further.
Ice caps begin to form.
The ice has a high albedo, reflecting sunlight and cooling the planet even more, a positive feedback loop known as the ice-albedo effect. This takes place too quickly for the negative feedback of silicate weathering to have an effect, so proto-lichens continue to weather rock in warmer areas and more CO2 is removed from the atmosphere, causing the temperature to keep dropping which makes the ice caps grow bigger, reflecting more sunlight.
As the ice sheets creep over the Earth, they pass a point of no return, a tipping point15, around 30° from the equator: the ice reflects so much sunlight that the ice-albedo positive feedback runs away and cannot be regulated. Earth plunges into a snowball state.
One scenario described by Lenton and Watson16 allows for pockets of proto-lichens and photosynthetic algae to have survived this glaciation. When some of the ice melted, perhaps from volcanic activity, the albedo effect went down, and temperatures rose. Proto-lichens then re-colonised the continents, increasing silicate weathering…and once again Gaia became a snowball Earth.
However, the cycle of glaciations and warmer periods did not continue during the Neoproterozoic, perhaps due to the decline in proto-lichens. Here’s one idea of how that might have occurred:
Gaia’s atmosphere had become enriched with oxygen by the activity of proto-lichens. Oxygen inhibited lichen photosynthesis by competing with carbon dioxide for the enzyme Rubisco which catalyses the reactions. CO2 removal from the atmosphere decreased, and the temperature rose. Figure 4 summarises the links between proto-lichen activity and the ratio of carbon dioxide to oxygen.
Thus, Gaia self-regulated her temperature through evolving relationships between the biotic and abiotic manifestations of her being.
One more astonishing influence of early lichen life can be seen as we move from the Neoproterozoic, which marks the end of the Pre-Cambrian, into the start of the Cambrian: an extraordinary eruption of multicellular life-forms can be found in the fossil record of 540 million years ago. Perhaps the proto-lichens had made conditions so cold that the only way for single-celled eukaryotic life to survive in isolated pockets of the ocean was to co-operate and pool resources. The Cambrian explosion gave rise to all the existing body plans that we find in today’s animals. It’s worth pondering that we might have the early lichens to thank for the emergence of our ancestors.
This essay has been a scientific exploration of the relationship between early lichens and Gaia…but I also have a personal relationship with lichens, who draw me into a deep experience with the ancient Earth.
Infinite and immortal, they grow timelessly across wind-rounded rocks and clothe the limbs of ancient trees. They are artists’ palettes spilled on sea-soaked boulders and red-daubed jam tarts laid out on granite plates. They angle their satellite dishes outwards to detect the language of a far-off place and time, and enfold the secret messages within their tissues.
Stephan Harding writes,
Gaia perception connects us with the seamless nature of existence, and opens up a new approach to scientific research based on scientific intuitions arising from scientists’ personal, deep ecological experience16.
Studying Gaia in this module has awoken childhood memories: of crustose Lecanora gazing calmly at me from rain-battered granite outcrops, asking me why people are adrift from the Earth; of Usnea lacework filtering pale sunlight in hazel woodlands, enticing me to enter their mysterious world; and of scarlet-tipped Cladonia inviting me to sip from their dew-filled cups.
I am now drinking from the cup of Gaia, and I accept her invitation to enter a deeper relationship. I’m also trying to answer her question about why we cut ourselves off from the source of our sustenance.
Lichens have much to teach us. In symbiosis, they live longer, grow more slowly, and utilise a wider range of substrates and materials for energy than the separate fungus and alga. This shows us how we, too, could live in co-operative relationship with other beings, to create a society which appreciates slow growth, re-cycling of materials, and diversification of sources of energy.
Both partners in lichen symbiosis take risks in their relationship: the fungus commits itself to a way of life in which it longs for an algal house-mate and cannot live alone; the alga is vulnerable in the hands of its larger and stronger partner, but chooses to participate in the collective harmony of lichen life. Together they are more resilient and know themselves differently. We, too, can step out into the open and let ourselves be vulnerable in Gaia’s hands, abandoning our misconception of separateness from nature. This will make us more resilient and allow our human species to know itself in a new way.
Satish Kumar is one of the founders of Schumacher College. On 11 January 2012, he met the M.Sc. Holistic Science students and said these words about falling in love.
Lichens are living beings which arise from a symbiotic relationship between a fungus and a unicellular photosynthesising organism, such as an alga or cyanobacterium. Both partners benefit from the association. Lichens can be found throughout the world in many different habitats, but this essay focuses on rock-weathering lichens that grow on silicate rock.
This is from background notes provided by Jules Cashford: “Gaia: From Story of Origin to Universe Story”, as part of Module Three on the M.Sc. in Holistic Science.
Scofield, B. (2004). Gaia: The Living Earth – 2,500 years of precedents in natural science and philosophy. In: Scientists Debate Gaia: the Next Century. Schneider, S.H., Miller, J.R., Crist, E. and Boston, P.J. (eds.) (2004). London: MIT Press, p. 152.
Lovelock, J. (2006). The Revenge of Gaia. London: Penguin, pp. 26-27.
Lenton, T. and Watson, A. (2011). Revolutions that Made the Earth. Oxford, OUP, p. 139.
Lovelock, J. (2004). Reflections on Gaia. In: Scientists Debate Gaia: the Next Century. Schneider, S.H., Miller, J.R., Crist, E. and Boston, P.J. (eds.) (2004). London: MIT Press, p. 3.
Lenton, T. and Watson, A. (2011). Revolutions that Made the Earth. Oxford, OUP.
Ibid. p. 270
Ibid. p. 268
Harding, S. (2006). Animate Earth. Dartington: Green Books, p. 118.
Lenton, T. and Watson, A. (2011). Revolutions that Made the Earth. Oxford: OUP, p. 110.
Ibid. p. 270.
Ibid. pp. 277-278.
Harding, S. (2010). Gaia Theory and Deep Ecology, p. 48. In: Green Spirit: Path to a New Consciousness, McCain, M. (ed.)
Ingold, T. (2011). Being Alive. New York: Routledge, p. xii.
“Why do we acknowledge only our textual sources but not the ground we walk, the ever-changing skies, mountains and rivers, rocks and trees, the houses we inhabit and the tools we use, not to mention the innumerable companions, both non-human animals and fellow humans, with which and with whom we share our lives?”17