The Deep Time Walk

This is an account of a Deep Time Walk with Stephan Harding that I was part of in 2011. I post it now because it give a clear picture of the evolution of Gaia as a living organism. In his teaching of Gaia theory Stephan has designed a series of experiential activities, which are intended to help people get in touch with living Gaia, the age of the Earth and its ancient process of evolution. The Deep Time Walk is one of these.

All those who learned from Stephan are deeply saddened by his death in September 2024. Read my tribute in the Guardian Other Lives

We start our walk on the cliffs of south Devon where signpost marks with the acorn sign of the National Trust points the way over a style down to the coastal path.  Stephan calls us into a huddle around him. He stands in front of us in his waterproofs and boots, blue woolly hat pulled over his ears, leaning lightly on his thumbstick. He gathers the group together, looks round eagerly at them to engage their attention, and launches off into words that leap between the discoveries of science and the mystery of anima mundi.  Neither takes priority: facts, figures and theories are expressed in the context of love for the living planet.

The start of a Deep Time Walk

We are here to experience the deep age of our planet.  Many of us know this theoretically, but today we are going to take a walk through deep time from Earth’s very beginnings up to the present moment.  Are you all up for that?

There are cheerful mutters of assent, and people huddle closer so as to hear better.

The Earth was formed 4.6 billion years ago.  Can you get a sense of how long that is? It’s really difficult, isn’t it? Now, it is 4.6 kilometres from here along the coastal path into Dartmouth, and we are going to walk it.  This means that every stride you take is about equivalent to half a million years.  Every millimetre is a thousand years.

Stephan gets out his rule and shows everyone what a metre looks like and measures it against his stride to show what he means. 

And this isn’t just theoretical—every stride you take is a stride on the surface of our actual planet.  I want you to feel the reality of this, that you are walking on our sacred planet that is 4.6 billion years old.

I look down at the mud and gravel and dirty puddles of the car park, which doesn’t feel particularly sacred just at the moment. I know what he means, but it’s not real for me yet.

OK.  Are you ready?  We begin here, 4.6 billion years ago.  Our planet has just formed as a molten ball swirling round the sun in space.  Everything is either molten rock or gas.  Nothing else.  And the sun is about 25% cooler than it is now. So follow me, remember every stride is about half a million years.

Along the Devon Coast

We follow Stephan over the style and down a muddy track toward the sea. People jostle together getting over the style, but soon string out along the path, some walking faster than others, some lingering to look at the scenery, some chatting. I walk in silence, counting my strides.  It is difficult to imagine this earth and the vast expanse of time.  I keep flipping into the present, noticing the slippery mud underneath my feet, the rusty barbed wire fence each side of the path, my muscles as they begin to stretch with walking.  Soon I lose count and start over again.

A little way down the path we climb over another style onto the coastal path proper. Stephan stops and we gather round to listen.

We have walked about 400,000 million years. Not much has happened.  The Earth has cooled a bit and something of a crust has formed, that’s about it.  Now, I suggest for the next section we walk along in silence, don’t allow ourselves to be distracted by the chatter.  Pay attention to each step as you take it as about half a million years.

I am relieved he has asked everyone to be quiet. I can get very cross with people chattering on walks like this. It is so easy to get into social chit-chat, or indeed discussions of what seem like important issues of sustainability. It is far more difficult to let oneself sink into this experience of deep time. How can I listen to Gaia if people are chattering around me?

We are now walking high up along the cliff top. To the west, Start Point reaches out into the Channel, long and green, fringed with rocky cliffs, punctuated at the southern end with its white lighthouse.  To the east we can just make out where the Dart Estuary tucks in behind Combe Point. The cool northerly breeze is countered by a surprising amount of warmth in the January sun. The sea is quiet, and smoothly reflects the clear blue sky. I can just hear the little splash of the waves as they kiss the rocks at the foot of the cliff. I walk along the short grass of the cliff top, one moment taking in the scenery and the next contemplating the millions of years as they pass underfoot.  How odd that this world we live in now was once a molten ball.

Stephan stops us a couple of times to explain key points in the early development of the planet.  He tells us how the moon was formed through a gigantic collision with another planet in very close orbit with the Earth.  And how the existence of the moon is essential for the development of life as we know it because it stabilizes Earth’s axial tilt, creating regular seasons.  He tells us how meteors from outer space collided with Earth bringing water—combinations of hydrogen and oxygen atoms formed in the explosion of early stars.  And as we walk on for another half kilometre or so, each stride half a million years along the cliff top, we experience millions of years in which the earth gradually cools and accumulates water, but no substantial changes happen.

We stop again at a high point where the path goes through a farm gate.   We wait for the stragglers to catch up, then Stephan talks to us again.

This is about 3.5 billion years ago. We have an Earth now with lots of ocean, delivered to us mostly by ice meteors.  We have a few volcanic islands, but no big continents at all.  And we have an atmosphere that is mostly carbon dioxide. If we were parachuted into the earth at this stage, we wouldn’t be able to breath and we would die.

We are all breathing deeply from our walk.  The effect of oxygen on our lives is very visible in pink cheeks and red noses. I notice the cold air as it goes through my nostrils.  Somewhere in the back of my throat I don’t notice it anymore, I have taken it in, and it is part of me.  Or am I part of it?  An Earth on which we couldn’t breath would not be our Earth.  But Stephan is still talking to us.

Now something quite remarkable happens when we walk through that gate.  That gate signifies the point where life begins.  The first life forms, we are pretty sure, were bacteria, still with us today.  Tiny little creatures that began to change the atmosphere of the earth.  But before we get into bacteria, let us first say good-bye to the pre-bacterial dead Earth that we have been walking on until now.

I look back in the direction we have come, about a kilometre with no life; and then forward toward Dartmouth.  There is a long way to go yet.

 When you go through the gate, see if you can allow yourself to feel something exciting, for something really new has come to pass on the earth: the appearance of life.

He looks round the group to make sure everyone gets the point.  His eyes slightly magnified by his glasses, Stephan has an open, engaging look when he is teaching like this.  He knows this stuff inside out and he clearly loves it.  His enthusiasm is infectious, so when he tells us we can experience the beginning of life, he give us permission of experience our world in a different way. We are almost inclined to believe him. 

And remember, throughout this whole walk, we are not talking about abstract academic ideas or computer modelling.  We are actually experiencing this very Earth herself. That’s who we are talking with.  She is right in front of us, right under our feet at this moment. This is her history, her story.

Follow me through the gate. Here we go, we are getting closer and closer, and then suddenly, life appears!  Can you feel the difference? Now there are bacteria. 

We bunch around him at the far side of the gate.  I suspect we are all wondering if we really experienced anything or whether it was just in our imagination.  But no matter, we are swept up in Stephan’s enthusiasm again.  He tells us about bacteria and the beginning of Gaia.

We don’t know how they first got going; there are lots of theories.  Bacteria are very complex beings in their own right, very adaptable, by no means simple. They needed hydrogen, and developed photosynthesis early on using sunlight to split hydrogen from sources like hydrogen sulphide gas. But this meant they were very limited in their distribution. Eventually they evolved to get hydrogen from water—a very difficult thing to do but once they learned how to do it the knowledge spread very quickly though swapping DNA.  And this released oxygen into the atmosphere, allowing the bacteria to spread all over the watery planet.  And that moment when bacteria cracked oxygen-producing photosynthesis I would say is the moment when Gaia was born. Some bacteria began to extract carbon dioxide from the atmosphere, and this of course began to cool the earth.  Others learned to decompose the dead bodies of the photosynthesisers, releasing methane into the atmosphere, thereby stopping the planet from freezing.  So you can see already life is adjusting the temperature of the earth through its interaction with gases in the atmosphere.

So now we are into Gaia.  A bacterial Gaia.  Still no continents, only oceans and volcanic islands. Little free oxygen, an atmosphere mainly composed of methane.

Stephan’s passion is for Gaia theory, how life profoundly affects the non-living environment, such as the composition of the atmosphere, which then feeds back to influence the entire living world. He describes this as a “tight coupling” between life and non-life out of which arises the ability of Gaia, of the earth system as a whole, to maintain key aspects of the global environment, such as global temperature, at levels favourable to life over billions of years, despite shocks from both within and outside itself.

Stephan teaching Gaia Theory on Dartmoor 2003

It strikes me how more complex the planet has suddenly become as we have walked through the gate.  Before the beginning of life, the Earth system was a relatively simple, non-living system, running down toward equilibrium according to the second law of thermodynamics.  Now a living planet is building toward a non-equilibrium state by drawing on the energy of the sun to build what scientists call a biogeochemical entity, or ‘one grand organic whole’ as Alfred Russel Wallace put it in the late nineteenth century.[2] 

I notice how the drama of walking symbolically through the gate has stimulated my imagination.  I feel my mind both reaching back in time and rooted in the present.  I see and enjoy the scenery and the experience of the walk, and at the same time this bacterial world has caught my imagination.

I walk on, thinking to myself, now life has arisen, things will move more quickly, we will see different life forms evolve.  How wrong I am. We walk on and on, down steeply toward the sea and then up again along a narrow path with dark thorn bushes on each side.  Some people start to talk again, but I try to keep my mind focussed on a million years for each stride through this bacterial world.   We walk about a kilometre before Stephan stops us next to another gate.

That was a thousand million years.  And all that time we had just bacteria.  We are now around 2,500 million years ago now when three important things happen.  One is that the bacteria start to get together to form a new kind of cell, the eukaryotic or nucleated cell.  They did this by co-operating with each other—they came together and melded into each other to create this new kind of cell—notice that most evolution occurs through co-operation, not competition.  These cells are what make animals like you and me, and plants, fungi and those others like amoebae. Two, as a result, photosynthesis became much more effective.  Oxygen began to accumulate in the atmosphere, not as much as today but enough to power up the whole biosphere. And the third thing that happened was that the first granite was formed and continents began to appear.  So there were large pieces of continental crust floating around, what we call plate tectonics started. So you get the picture?  We are in a two-cellular world now, bacteria and eukaryotic cells like algae, both of which of course are still around today.

Stephan explains that there is still a long way to go before we get the first multi-cellular organisms in the fossil record, but he points out that all the time the biotic world is getting more complex, and probably better at self-regulation.

So, when you go through that gate, again you can feel a rapid acceleration in the psyche of Gaia.  Suddenly she has discovered this new psychological possibility—eukaryotic life, with all the possibilities and innovations that brings with it, and maybe she’s aware that one day there will be intelligent life, lumbering around, doing a walk like this.

Remember, it is not some abstract Earth, it is this Earth we are talking about

And so we walk on, and then on more.  The path takes us up another rise, and the steeply down to a rocky patch just by the sea.  A wooden bridge takes the footpath over a long split in the rock, and even with today’s tiny waves the sea surges up and breaks in a cave at the end with a roar that echoes around the rocks.  We begin to crowd around Stephan to hear the next phase of the story, but he tells us we are just stopping for a rest. 

Nothing much has happened, just bacteria and single celled eukaryotes. Maybe they are beginning to colonize the land.  But no other significant changes.

The winter afternoon is drawing toward its close.  The sun is dropping and with it the blue of the sky is deepening. The horizon strikes a sharp line across the world. As the sun drops toward the horizon in the west. We can see across the mouth of the estuary of the Dart now, and above the cliffs on the far side the nearly full moon is rising in the evening sky, vast and pale over the fading green fields.  We tease Stephan that his animist thinking has brought us to this spot where we can see moonrise just at the right moment.   “So that moon,” I think to myself, “is not just wondrous, not just influencing the tides, as I have always known, but is part of the stability of the Earth.”

And we press on again.  Still every stride is half a million years.  Still only bacteria and single celled eukaryotes. All this time. Still no plants, no animals, no fungi.  Maybe a smear of green photosynthesising algae around the fringes of the land masses. Very little oxygen.  Stephan again urges us to walk in silence and to feel that this is the history of the actual palpable earth beneath our feet.

We pass the point of a billion, a thousand million years ago, and walk on, and on for another 400 million years, turning inland as the path winds along the estuary, the moon now hanging higher and brighter in the sky to our right across the water.  The rough going of the coastal path gradually gives way to more urban pedestrian footpaths through more park-like surroundings.  We drop down through woodland toward the river, down steps and onto a paved area outside Dartmouth Castle. The castle was originally built to guard the entrance to the river but is now a teahouse. Stephan calls us together.  

At this point, something very important happens. Come on, gather round… This is the tea-room at the edge of the Cambrian explosion,” he jokes. “At this point there is a dramatic increase of biodiversity in the fossil records. We just passed a major ice-age, a snowball earth, but here around six hundred million years ago all over the planet we find hard-bodied organisms as fossils: multi-cellular creatures, animals like the famous trilobites.  And from now on, things are going to happen very, very fast.  No plants yet:  the basis of the food chain is still unicellular algae and bacteria.  And very important, at this point because a lot more carbon was being buried the oxygen level goes up to maybe 15%.

There is a lot of excitement as this part of the story unfolds. People ask lots of detailed questions about why this happened at this point. We walk on again, but only a couple of hundred strides before Stephan stops us again. 

480 million years ago, lots of things happen, including the first fish and the first land plants, which are still with us today – they are the mosses, and they began to weather rock very effectively and that in turn helped to regulate the climate of the Earth—if you weather the right kind of rock you take carbon dioxide out of the earth’s atmosphere.

I remember earlier stories from Stephan about how biologically assisted rock weathering increases the rate of carbon sequestration significantly. He reminds us that that the sun has been getting hotter throughout the history of the earth, and in present time is some 25-30% hotter than when earth first formed.  This, he says, shows the extraordinary feature of Gaia’s self-regulation—that through the interaction of living beings and the material world the temperature has stayed within the limits appropriate for life.

We walk on and developments come much faster. We pass the point where ferns develop and hear how the biodiversity of land plants and fish in the ocean starts accelerating. We walk through the Devonian period 400 million years ago, when the rocks of this area of England were laid down. We go on through the Carboniferous period, when amphibians moved onto the land and plants developed wood.

Stephan pauses longer here to emphasize a point about Gaian self-regulation.

The evolution of wood created a very serious problem, a significant dip in global temperature. Creating wood sucks carbon dioxide out of the atmosphere, and at this stage nothing could break it down.  So when the trees fell into swamps they didn’t rot, they were crushed into rock, which is where coal comes from. So life could have frozen itself close to death by extracting so much carbon dioxide from the atmosphere that it would have set in train a snowball earth episode, a massive global ice age.  In the end it was the fungi that cracked the secret of breaking down wood, release carbon back into the atmosphere thereby saving the earth from freezing to death. This is a classic Gaian situation, where Gaia teeters on the edge of catastrophe from the impact of one of her life forms, and then another life form comes in and rescues the day at the very last minute.

We are walking along the road into Dartmouth now, pausing now for updates every 50 yards or so. We go through the lower Permian, 300 million years ago, when the continents came together to create the mega continent Pangaea; through the Permian mass extinction some 250 million years ago, probably caused by the supercontinent itself; on to the upper Triassic, the beginning of the age of reptiles; through the lower Jurassic, when Pangaea begins to split up into the continents we are familiar with now. At 136 million years ago we enter the lower Cretaceous, when the land burst into colour and perfume with the appearance of the first flowering plants and a new pollinatory symbiosis with the insect world.

In comparison with the earlier period walking along the cliff top—which feels so distant now—when nothing changed for millions upon millions of years, now development piles on development, as evolution creates new life forms which in turn influence the ecology of the planet as a whole. We keep pausing for updates, even though Stephan is now only picking out the key points.

We make a longer stop at 65 million years ago. 

This is an important moment. This is the last great extinction, when the dinosaurs disappeared, almost certainly because of a ten kilometre meteorite hitting the earth. It wiped out about 65% of all the life forms, probably over a few centuries through changing the climate. The little pipsqueak mammals that were running around the toenails of the giant dinosaurs suddenly had the whole world to themselves, and they diversified to create the life forms we have today.  And we still have some of the direct descendents of dinosaurs around, of course, in the birds.

We walk another few hundred yards along the river bank, to where Stephan stops on a slipway down to the river.  It is almost dark.  The streetlights are beginning to envelop us in their orange glow.  Out on the river one or two boats are moving. I watch the red port and white steaming light of a fishing boat appear round the headland where the Castle nestles next to the river.  It is a calm and quiet evening in the early twenty-first century. Stephan squats down on the ground, pulls out his tape measure again, and lays out just 30 centimetres of it on the ground.  It seems unbelievably short.

Stephan demonstrating the last 300 thousand years

Now we have the last 30 centimetres – the last 300 thousand years.”  He gestures to the far end of the rule.  “Back here is when we have the oldest remains of Homo sapiens. Here at 1.3 centimetres, 13,000 years before the present, that’s the end of the last ice age.  Then at about eight millimetres, 8,000 years ago, we have the start of the farming revolution.”  We are all peering down, trying to make out the tiny intervals he is pointing to on the rule. “Then six millimetres, 6,000 years ago, the beginning of civilization in Egypt and Mesopotamia. 2,000 years ago, two millimetres from the end, that is the beginning of the modern calendar, and then about 300 years ago, with is 3/10 of a millimetre so you can’t see it, we have the industrial revolution. From this point human beings began to change the climate of the Earth in a very serious way; and also began to destroy the huge diversity of life that has been building up over hundreds of millions of years.  Welcome to the present moment!

Photo: Jan Van Boeckel

We gather together by the riverside in a moment of silence to notice the length of the walk, the huge expanse of time which we have traversed in our imagination, the massive age of the earth.  Stephan asks us to think back to the beginning of our walk when there was no life; then to remember the long period where there was only unicellular life; and how when we reached the teahouse at the Castle there began an explosion of multi-cellular life.  He reminds us of the challenges Gaia had faced, the ice ages, the extinctions, the sun forever getting hotter. And he asks us to see just how recent is our own industrial civilization. 

Take a moment in silence to connect with the immense age of the Earth—and remember that we are connecting with this Earth.  Notice the intelligence that has been developing over geological time. Gaia has become more skilful at handling the sun, at regulating her surface through the interaction of life, rocks, atmosphere and water. The ancient biosphere is still with us in our guts, and in the soil; it is still with us in our mitochondria.  You might then feel a sense of reverence to this vast being you are a part of.

It is quite dark now.  I stand looking out over the water with my mind divided. In part I am just loving present moment, the fresh evening air, the physical exhilaration of a good hike, the way the quiet flow of the river reflects the lights of boats and the moon.  I am appreciating the company of my fellow walkers, all of whom seem to be deeply engaged in the story we have shared. But in part I am left behind, in that incredible period of time, walking on and on along the coastal path, treading half a million years with each stride, when there was nothing living on earth but bacteria and eukaryotes.  And in part I am contemplating that last bare 30 centimetres which brought us to the present time: how the drama of human history, and all these roads and houses and boats, the carbon fuels, the plastics, the electricity, are crammed in the last fractions of a millimetre.

I had some sense of this vast expanse of pre-history, but walking it took it more deeply into my bones.

For more information visit the Deep Time Walk website, and Deep Time Community which includes Deep Time Cards and other training materials that unpack a history of our Earth. The Deep Time App enables anyone, anywhere to experience a walking audio history of the living Earth. As you walk through time, the dramatised audio narrative combines scientific evidence with poetry to tell the story of Earth’s formation.

Stephan Harding and Robert Woodford have written a paper on the experience of the walk in the Journal of Sustainable Education: The Deep Time Walk – How Effective Is It?

Listen to the spoken version of the Deep Time Walk with Stephan at Outrage and Optimism

POSTSCRIPT. You don’t have access to the Devon Coast to do a Deep Time Walk. This map shows the route taken around St James and Green Parks in Central London by Deborah Colvin and Sara Mark, with the at St James’s Church Piccadilly Eco-contemplative group

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[1] Harding, S. P. (2009). Animate Earth. Foxhole, Dartington: Green Books.

[2] Quoted in Crist, E., & Rinker, H. B. (Eds.). (2010). Gaia in Turmoil: Climate change, biodepletion, and earth ethics in an age of crisis. Cambridge, MA: The MIT Press, p.3