Change in the context of Deep Time

Putting deep time on a familiar scale helps us to understand the rapid pace of today’s changes. The expanse of deep time still surprises me every time I look at it, hopefully it will impress you too.

This photo of a road cutting near where I live shows layers of old red sandstone that were laid down in the Emsian stage of the Lower Devonian between 393 and 407 million years ago. At the time this piece of England was at a tropical latitude of 17º south (52º north today) with a warm or hot semi-arid climate to match. The area would have resembled Death Valley with the decaying Caledonian orogeny feeding the sandstone across a desert from the mountains stretching across what’s now Scotland, Ireland and north America. There were no land animals and the forests were only inches tall and restricted to shorelines and estuaries. But how long ago is 400 million years, is that a lot?

In discussing paleoclimate, time periods like 125 thousand, 3 million, even 1.4 billion years and so on are often quoted. They are however very difficult for our minds to comprehend. We have not evolved to deal with time on this scale. In fact, as I get older, even the concept of ten years has changed significantly since I was a teenager. I’m convinced my 20s lasted at least three times as long as my 50s.

A common way of dealing with geologic time is therefore to apply it to a scale that we are more used to. A day or an hour are just too small for this task, but applying geologic time to a calendar year works pretty well, and allows us to visualise eons, eras, periods, epochs and ages.

To paraphrase Douglas Adams, the Earth is old, very old.

The earth formed 4,570,000,000 (or 4.57 billion years) ago. This marks 00:00 on January 1^st of our calendar year. The moon was formed following a collision between the proto-Earth and a smaller proto-planet on the morning of January 5^th. The first life is thought to have emerged by March 3^rd but it wasn’t until August 10^th that larger complex cells evolved. The Cambrian explosion of complex life happened between November 19^th and 20^th but many of the previous lifeforms such as sponges had been about since the start of November. Mosses and plants came out of the water from November 26^th and on November 30^th lungfish crawled out of the water, followed by the first amphibians on December 4^th. Lizards first appeared on December 12^th. Over the following weeks dinosaurs and mammals co-evolved and dinosaurs ruled the planet until the famous asteroid impact ended their reign, leaving only the birds from their line on the afternoon of December 25^th. They ruled for so long that by the time Tyrannosaurs evolved, Stegosaurus had already been extinct for nearly 80 million years (6 days).

What we consider as ancient history didn’t start until the closing minutes of December 31^st. Homo Erectus first used fire at 8:21pm, humans moved out from Africa at 11:49pm, establishing the oldest known settlements ten minutes later at 11:58pm. Julius Caesar came to power just 14.3 seconds before midnight and man landed on the moon just 0.37 seconds before the fireworks mark the new year.

On this timescale the universe came into existence almost exactly 3 years before our earth time scale starts. The earth has therefore seen a quarter of the age of the universe.

Ice Ages

It’s interesting to look at the time scale of the current ice age on our calendar year. The ice age started 2.54 million years ago or at 19:12 on December 31st, although the Antarctic ice sheet started to form on East Antarctica much earlier, in the early morning of December 28th (35 million years ago).

For the first part of the Pleistocene the glacial cycles were rapid only lasting 40,000 years on average (4 minutes and 35 seconds) until they switched to the longer 100,000 year glaciations around 780,000 years ago marking the start of the middle Pleistocene age (22:30 on Dec 31st).

The previous five interglacials before the upper Pleistocene and Last Glacial Maximum happened at 23:05 for the Anglian, 23:14 for the Hoxnian, 23:24 for the Purfleet, 23:32 for the Averley and 23:46 for the Eemian just 126,000 years ago.

The Last Glacial Maximum when an ice sheet stretched from Scandinavia across the North Sea and over much of the UK to within 20 miles of where I live in the west Midlands was at 23:57 and 21 seconds on December 31st. Shortly after the Earth’s orbit dragged us out of the glaciation. There was a hiatus at 23:58 and 32 seconds known as the Younger Dryas when the melting Laurentide ice sheet, which covered Canada and much of North America, melted, disrupting Atlantic currents, cooling the northern hemisphere briefly (for about 9 seconds). After that the Holocene emerged at 23:58 and 39 seconds to midnight.

The fastest warming was between 16,000 years ago and the start of the Younger Dryas northern cooling at 12,900 years ago. In that time, global temperatures rose by 6ºC. The warming rate was therefore 0.019ºC per decade. Today’s warming rate is 0.27ºC per decade - 14 times faster!

Fossil fuel deposits

An important insight this scale provides us with relates the laying down of fossil fuels and their subsequent extraction and burning by us. The Forest of Dean is close to where I live, and was a major coal area back in the day. The coal was laid down during the aptly named Carboniferous period between December 2nd and 7th, a time span of 60 million years.

The coal measures are separated by layers of marine limestone. At the time, the earth was within another ice age, but due to the position of the land around the equator at the time, the local effect of the glaciations and deglaciation was on sea level. Just like the current ice age, the Earth’s orbit provided cooling and heating on a roughly 120,000 year cycle. During long (100,000 year - 12 minutes) cold periods, sea levels dropped to allow the land in the Forest of Dean to emerge as a tropical coastal swamp with seasonal rains allowing a dense forest to thrive. Fallen trees sank into the swampy mud, locking away the carbon they had taken from the environment to grow. During the shorter (20,000 year - 2 minutes 25 seconds) warm periods, sea levels rose over the forest, allowing a marine deposit of limestone to cover the area, trapping in the stored woody remains. Over the following hundreds of millions of years, the woody deposits were mineralised into coal. The forest of Dean has 13 such layers of coal, suggesting 13 glacial cycles, but other fields across the UK had many more . This process accumulated roughly 1.5 million years of gently and gradually sequestration of carbon from the ancient atmosphere and store away the solar energy used to create it. On our time scale this is a total of 3 hours.

Although artisanal mining had been in progress since the Roman times, serious mining ran between 1820 and 1965, ending when it was all economically extracted. On our timescale it therefore only took humans 1 second to extract and burn what nature had taken 3 hours to sequester.

The whole period used by the IPCC to describe the post industrial world started in 1850 and runs through to today. That’s from 23:59 and 58.8 seconds to midnight. The last 1.187 seconds of our year.

This is just a tiny local coal field, affected by the glacial cycle. Appalachian fields for example were laid down continuously for much of the Carboniferous spanning days on our time scale. It has still taken us just the 1.187 seconds to extract and burn it though.

Oil and gas are no different, they just come from different sources. They are mainly laid down as deposits of plankton bodies that have sunk to the bottom of seas and been subsequently buried by overlying deposits of rock allowing them time and elevated temperature to degrade to oil and gas. The time spans are similar. The Permian basin in Texas, the source of half the worlds petroleum from the epoch, is a complex structure that accumulated marine carbon deposits over a period of 67 million years from the 5th to the 10th December, 5 days. But it has still only taken us just 1.187 seconds to extract and burn a great deal of it.

This is the driver behind the current Carbon Pulse. The unprecedented release of carbon from the mineral earth that was stored away over very long time periods. The only natural equivalents are massive volcanic eruptions. How do they compare?

Natural Carbon Pulses

There is a natural ebb and flow of carbon within the geologic system, often simply called the carbon cycle. Tectonic and natural processes both release and absorb carbon, usually in the form of CO₂, through volcanic activity, rock weathering and biogenic processes such as photosynthesis and decay. Limestone for example contains a great deal of carbon in the form of calcium carbonate. This is because trillions of tiny marine creatures use the mineral to create their tiny shells, when they die, the shells drop to the ocean floor where they accumulate storing away the carbon used in their creation. The white cliffs of Dover like many others around the world are piles of tiny shells accumulated over millions of years and buried away, storing the carbon with them. When limestone comes into contact with even mild acids, carbon dioxide fizzes out of the rock. That’s why you shouldn’t cut lemons on your marble worktops - marble is highly compacted (metamorphic) limestone rock.

Tectonic and volcanic processes emit the most carbon dioxide. Huge eruptions have occurred in the past called large igneous provinces. The map below from the much cited Bond & Grasby paper¹ shows their extent. The most infamous is the Siberian Traps.

The Traps are a huge area of basalt lava (4 million cubic kilometres) that erupted over a period of 2 million years (4 hours) spanning the Permian and Triassic boundary 252 million years ago, on the evening of December 10th.

The pulse of carbon dioxide was made worse by the erupting lava burning through a huge coal deposit releasing this store of carbon in addition to the volcanic discharge. Atmospheric CO₂ concentrations rose from approximately 610ppm in the Permian up to between 840 and 1,200ppm at the start of the Triassic. This created a pulse of warming, increasing mean temperatures by 8ºC and caused the greatest mass extinction event in Earth’s history, the Great Dying.

Looking at the timing more closely. Although the Traps erupted over a 2 million years period, (4 hours) The peak emissions and temperature rise was over just 60,000 years (6 minutes and 51 seconds). Our current rate of temperature rise to 1.45ºC in 125 years is therefore 86 times faster than the rise that caused the greatest mass extinction in Earth’s history. That’s being a little generous since the warming hasn’t been linear since 1900. Todays decadal rate is 0.27ºC per decade, so a little over 200 times faster!

It took complex life 8 million years to recover to the same level of biodiversity, that’s 16 hours on our timescale. Part of the reason for this was the very long time it took the natural system to sequester the additional carbon, believed to be about 5 million years (10 hours). A new paper² suggests this was due to the forests of the time passing a collapse tipping point, wiping them out and removing their ability to sequester the CO₂ from the atmosphere. Coupled with the 97% loss of marine species, natural carbon sequestration collapsed leaving the CO₂ in the atmosphere for far longer than it would otherwise have been. A poignant reminder of the importance of the current rain forests and marine ecosystems that provide the same services today, but are under threat from our actions.

One of the most interesting warming pulses in the past was the transition between the Paleocene and the Eocene 56 million years ago at 13:21 on December 26th. This is known as the Paleocene-Eocene Thermal Maximum or PETM. This is the fastest prior warming in Earth’s history and is believed to have been caused by a huge release of CO₂ from the North Atlantic large igneous province as the continents of North America and Europe split apart, opening the north Atlantic Ocean.

Temperatures rose by 5ºC over just 5,000 years (34 seconds of our year). This is still over 27 times slower than our current rate of warming though. It took 200,000 years (2 minutes and 20 seconds) for the carbon pulse to be absorbed through natural processes returning the climate to its previous state.

Estimates vary but range from 2,000 to 7,000 gigatons of carbon being emitted during the PETM, driving the temperature spike. This gives an emission rate of between 0.4 to 1.4 GtCO₂/year. According to the Global Carbon Budget 2024³ published in March. Human emissions in 2024 totalled 40.6 GtCO₂. We are therefore currently emitting CO₂ between 30 and 100 times faster than caused the PETM, the fastest warming period in Earth’s history, and also by the way, a mass extinction event.

The graph below puts our current predicament into context. From a geologic perspective, our current warming is literally off the scale.

A 6th mass extinction

The scientific definition of a mass extinction event is a 70% species loss within a period of 2.5 million years. 2.5 million years is 4 hours and 48 minutes on our timescale. The current human assisted extinction event started just 15,000 years ago (1 minute and 46 seconds), so we are only 0.6% of the way through the allotted time. We’ve made a strong start though.

In this time for example, we have successfully wiped out most northern American and European magaforna with only the exceptions of bison, moose and reindeer. The Mammoths, Mastodons, Giant Sloths, Wholly Rhino, Dire Wolves, Giant Elk, Sabre toothed cats, northern Lions, European Hippopotamus and horses which made it through the previous warmer interglacials are all gone. (What we think of as wild horses are all from a single line of domesticated animals from Asia, all previous global species have been eliminated.)

We’re speeding up though, the current extinction rate is 1,000 times above the natural baseline. It’s the rate of environmental change that is driving this rate. Plants and animals need time to evolve into new niches and changing circumstances. This often involves moving to more suitable regions. Lower latitudes during cooling and higher latitudes during warming. This is particularly evident with fish stocks and marine creatures currently since their metabolism is controlled by their surrounding water temperature. Species don’t just pack up and move through. They slowly expand into suitable ranges over generations often with evolutionary changes on the way, and die out in less suitable ones if they can’t adapt. This takes time though and this is what makes the current, unprecedented rate of change so destructive.

What about the future?

1 Second passed midnight

Let’s start with a tiny jump, just 1 second into the future. The year will be 2180.

By then the results of the current policy turmoil will have played out. There is obviously a range of outcomes, but I’m prepared to bet that the likely temperature will be above +3ºC. This is because the current level of acceleration and growing Earth Energy Imbalance suggests a high climate sensitivity to greenhouse gases. It is also very unlikely that carbon capture, both naturally based or technological, will have been successfully scaled to the point where it can start making a difference.

We may have achieved significant emissions reductions, possibly even net-zero, but through a combination of global economic collapse and panic based closure of fossil fuel infrastructure, rather than an orderly policy based approach.

The world will look quite different, not just through the rise in sea levels which will probably be 2m or more and rising at 10-30mm a year, but from spreading deserts in the sub-tropics with some forest expansion at higher latitudes.

It doesn’t have to be like this though. If we take decarbonisation seriously we may have capped temperatures closer to +2.5ºC and only have 1m of sea level rise. The mass human exodus from the tropics and sub-tropics could also have been largely averted, but only if we act decisively in the next quarter of a second.

A number of tipping points are likely to have been crossed. Tropical coral ecosystems will certainly be extinct, that will happen within the next quarter of a second regardless of our actions now. The Amazon will probably have passed it’s tipping point and be well on the way to being a savanna. The AMOC, the Atlantic current that brings warm conditions to western Europe will be significantly weaker and may even have started to collapse. Once its tipping point is reached, it will take 50-100 years to completely collapse, so there is a fair chance it will be at least 75% reduced. The chaos this will cause in Northern Europe and the tropical rain belts will be tremendous.

The other possibility is that we have started geoengineering the atmosphere through stratospheric aerosol injection, forever increasing it year on year to balance any continued emissions and fight feedbacks triggered by tipping elements. Changing global weather patterns and water resource changes may have triggered regional wars or worse. The world may live in fear of the termination shock when the geoengineering is no longer affordable.

Our behaviour in the next 10-15 years (0.07 to 0.17 seconds) will have a huge effect on the next second of Earth’s history.

1 minute into January 1st

Next we take a big jump of 8,695 years. This is an interesting jump because without human caused emissions and climate change, the world would be cooling and heading into the next phase of glaciation, dictated by the orbital wobbles known as the Milankovitch cycles.

We have already cancelled this event however. A large enough proportion of the CO₂ and NO₂ already emitted will still be in the atmosphere, keeping temperatures high enough to prevent the regrowth of the ice sheets.

Not only that, but during the minute of elevated temperatures, both Greenland and the West Antarctic ice sheets together with all the world’s glaciers will have completely collapsed and melted away. The East Antarctic ice sheet will still exist but will be in serious decline. Sea level rise may be as high as 40m by this time. Re-starting glaciation from scratch will require a higher orbital forcing or a significant reduction in greenhouse gas forcing. Such an orbital cycle linked to greenhouse gas natural sequestration may allow a glaciation to start after 200,000 years or so (30 minutes).

Our current civilisation will have completely disappeared. Humans are likely to survive in pockets but not in the tropics. Depending on how gracefully our civilisation collapses, nuclear fall out from either war or nuclear power accidents caused by neglect, may have rendered wider areas also uninhabitable.

Alternatively we may have mastered global carbon and atmospheric management. We may have developed a fully sustainable circular economy with zero waste that exists on clean power and responsible management of the ecosystem, including human population, even limiting sea level rise to less than 10m.

Our behaviour in the the next century and a half (1 second) will also have a huge effect on the next minute of Earth’s history.

1 hour into January 1st

Now we jump over half a million years to 521,689 years ahead. By this time, natural processes will have scrubbed the air clean of our emissions and the world will have largely forgotten we existed. Enough greenhouse gas will have been removed from the atmosphere that the Milankovitch cycles can re-take control and re-establish the ice age. It will likely be a slow start with little or no ice cover on Antarctica, so potentially a long period of short glacials just like the early Pleistocene.

The ecosystem should also have stabilised with new plants and animal groups starting to evolve into the newly created niches. The beginning of the end of the 6th mass extinction if it’s lucky.

Other changes will have occurred. It’s likely that Africa will have moved northward closing the Mediterranean and cutting it off from the world’s oceans. It will have started to evaporate becoming highly saline and descending to a canyon system fed by rivers to a large saline lake with gypsum deposits. Life in the sea will likely die out except for saline tolerant bacteria.

The Yellowstone volcanic system may also have erupted in this time, flooding the area with basalt lava and emitting significant quantities of CO₂. Perhaps enough to continue the de-glaciated state, even tipping the world out of the ice age all together and into a new hot house regime. This could continue and deepen the 6th mass extinction event.

January 2nd

One full day into the future is 12.5 million years. Our plastic and concrete layer will be part of the strata with some plunging deep into the earth to be recycled. North Africa will be subducting under Europe finally eliminating the Mediterranean, which is actually the last vestiges of the ancient Tethys Ocean. A new mountain range will be growing in it’s place.

Australia will have moved further north, starting to raise a plateau across Indonesia, the start of an another new mountain range. Antarctica will be closing the gap with south America. Once closed, the great southern ocean circulation will cease allowing warmer conditions on the continent, finally melting the ice sheet and ending the ice age.

Other plate movements are harder to predict. When India split from Madagascar and started moving northwards, the pace was gentle. In fact at its original speed, it wouldn’t have hit Asia even now. It would be an Island surrounded by ocean with a unique ecosystem of its own. In reality it was accelerated by a huge mantle plume which shot it across the Ocean to collide with Asia and raise the Himalayan and Tibetan Plateau 20 million years early at 10am on the 29th December.

On a rough average, the Earth seems to form supercontinents in a 250 million year cycle. We’re at the halfway point currently, but the next one may have started to form by January 2nd. The African collision could open a tear in the Atlantic starting its closure from the East, raising a new mountain range up the west African coast. Spain may rotate clockwise, closing the Bay of Biscay.

One thing is for sure, even if we have started a 6th mass extinction, by this time life will have recovered, producing new and beautiful systems that we can’t imagine.

I like to think that birds will rise to supremacy. They are amongst the most intelligent and adaptable group on the planet today, recently thriving in every corner before we interfered. It’s a nice thought that the Dinosaurs, left with just one lineage after the asteroid impact, may once more rule the world, suffering only a brief pause when an unruly offshoot of the mammal group stuffed it up briefly, then handed back the dice a few seconds later.

The deep future

January 8th to 20th

One week into the new year is 87.9 million years into the future and significant plate tectonic movements will have occurred. The new supercontinent will be well on its way to formation. The world map will feel familiar but oddly different. In a 2020 paper, Hannah Davies et al⁴. suggested four potential future supercontinents, derived from different plate tectonic processes, with different oceans opening and closing. All are possible and there is no way of us knowing which, if any are correct. It’s an interesting perspective though. Here are the four scenarios at 1 to 3 weeks into January.

Next year

Towards the end of the year, the Sun will start to run out of hydrogen fuel and start to burn helium. The increased solar radiation will burn off the Earth’s atmosphere completely, ending the great experiment of life on Earth. In about 15 months time (6 billion years), the sun will transform into a red giant pushing the habitable zone out to Jupiter and eventually engulfing the inner planets, including the Earth. After a period of rapid Helium burning, this too will run out and a beautiful planetary nebula will form as the sun’s core collapses into a neutron star, expelling the outer layers into space. Every atom you are made of and are surrounded by will be blown out into the cosmos in the form of interstellar dust like the Hubble Space Telescope image below.

In future years the cloud may be merged into a new solar system, with a new sun, planets and maybe even life.

1. David P.G. Bond, Stephen E. Grasby, On the causes of mass extinctions, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 478, 2017, Pages 3-29, ISSN 0031-0182, https://doi.org/10.1016/j.palaeo.2016.11.005

(https://www.sciencedirect.com/science/article/pii/S0031018216306915)

2. Xu, Z., Yu, J., Yin, H. et al. Early Triassic super-greenhouse climate driven by vegetation collapse. Nat Commun 16, 5400 (2025). https://doi.org/10.1038/s41467-025-60396-y

3. Friedlingstein, P. et al. Global Carbon Budget 2024, Earth Syst. Sci. Data, 17, 965–1039, https://doi.org/10.5194/essd-17-965-2025 , 2025.

4. Davies, H., Green, M., & Duarte, J. (2020). Back to the future II: Four views of future tides. Earth system dynamics, 11(1). https://pure.bangor.ac.uk/ws/portalfiles/portal/28554742/esd_11_291_2020.pdf