The Anthropocene

Foundations

Start with the verdict

In March 2024, the International Union of Geological Sciences confirmed that the proposal to add an Anthropocene epoch to the geological timescale had been rejected.

It had got a long way. A working group had been running since 2009. It had voted in favour of a formal epoch. It had chosen a candidate golden spike: a small, deep, exceptionally still lake in Ontario whose sediments lay down clean annual layers. The papers were written and the case was made.

The parent subcommission voted it down, and the rejection was confirmed. Some members of the working group disputed the procedure, and that dispute was reported alongside the result.

So: we do not live in the Anthropocene, formally. We live in the Holocene epoch, as we have since the last glaciation ended.

And here is the sentence this lesson exists to deliver: not a single piece of the underlying evidence changed.

That combination is worth sitting with, because it is a clean example of something this course keeps returning to. Evidence and classification are different things. A vote can change what we call something. It cannot change what is in the sediment.

What the evidence actually is

The case for a stratigraphic signal is strong, and it does not depend on the vote.

The bomb spike. Between 1952 and 1963, atmospheric thermonuclear testing put plutonium-239 and a doubled radiocarbon signal into the whole atmosphere. It came down everywhere, within a few years, and it is in sediments and ice from the Arctic to Antarctica.

For stratigraphy this is close to ideal. Plutonium-239 has effectively no natural source. The rise is sharp, the peak is dated, and the decline after the 1963 test-ban treaty is equally sharp. It is the most globally synchronous marker in recent sediments, and it will be detectable for a very long time.

Fly ash. Spherical carbonaceous particles produced by high-temperature fossil fuel combustion, distributed globally by the atmosphere, and geologically distinctive.

Technofossils. Concrete, of which humanity has now made enough to cover a substantial area of the planet’s surface. Aluminium, which essentially does not occur in metallic form naturally. Glass. And plastics, which are geologically novel, are now found in deep-sea and polar sediments, and do not degrade on any timescale that matters here.

Nitrogen isotopes. Lesson 8.4’s Haber-Bosch reaction has an isotopic signature, and it shows up in the sediments of remote lakes that never saw a fertiliser bag.

Fossils. The domestic chicken is now the most numerous bird on Earth by a very large margin, its skeleton is unlike any wild ancestor’s after decades of selective breeding, and its bones are being deposited in enormous quantities. Future palaeontologists will find a chicken horizon.

Add the carbon isotope shift from burning fossil carbon, the sea-level and temperature records, and the extinction signal, and the sedimentary record of the mid-twentieth century really is different in kind from anything below it.

So why was it rejected?

Three reasons, and only the third is about the science being wrong — and it is not exactly that either.

It is very short. Epochs are typically hundreds of thousands to millions of years long. The proposed Anthropocene would be about seventy years, sitting inside the Holocene, which is itself only about 11,700 years. Some stratigraphers regard a unit shorter than the resolution of much of the geological record as a category error.

It truncates the Holocene. Formalising the Anthropocene ends the Holocene in 1952, which is a substantial change to a well-established unit made on the basis of a very thin sliver of section.

Human impact is not synchronous. This is the strongest argument, and it is Gibbard and colleagues’. Farming began at different times in different places over thousands of years, as chapter 7 described. Deforestation, extinction and land conversion are spread across millennia. Picking a single global base date makes the change look like an instant when the evidence says it is a process with a long and uneven history.

Their alternative is that the Anthropocene should be treated as a geological event.

Event versus epoch, and why this is not a demotion

This distinction is the intellectual payload of the lesson, and it is routinely misreported.

Geology uses both categories, and events are not lesser.

Lesson 5.4 was about the Great Oxidation Event. That is not an epoch. It has no golden spike. It is one of the most consequential transformations in the history of the planet, and it changed the atmosphere permanently. Nobody thinks its status as an event makes it small.

The Cambrian Explosion of lesson 5.6 is likewise an event, not a formal time unit.

An event is a described happening with a duration and a set of consequences. An epoch is an administrative container with a defined base, used for correlating rocks between continents. Calling the Anthropocene an event says it is real, global and consequential, and that it does not have a single clean starting line.

Which is, on the evidence, true.

The dates that were on the table

Because the choice of start date is not a neutral technical matter, and Lewis and Maslin made this explicit.

1610, the Orbis spike. Antarctic ice records a dip in atmospheric carbon dioxide around 1610. One proposed explanation is the American depopulation of lesson 8.1: tens of millions of deaths, farmland reverting to forest, and that regrowth pulling carbon out of the air. The attribution is debated, and other contributors have been proposed.

Choose this date and the Anthropocene begins with colonialism and a demographic catastrophe.

1964, the bomb spike. Choose this and it begins with industrial and nuclear modernity, and the responsibility looks different, and more recent.

Both are defensible stratigraphically. They tell different stories about what this period is, and about who did it. That is a good example of a general principle: where a boundary is drawn often encodes an argument, and it is worth asking whose argument.

The extinction question, stated honestly

The extinction evidence is frequently overstated in both directions, so here it is with its uncertainty attached.

Current extinction rates are estimated to be far above the background rate inferred from the fossil record. Different methods give different multipliers, and the estimates are sensitive to assumptions about how many species exist and how many undocumented extinctions have occurred.

But the losses documented so far have not yet reached the magnitude of the five great mass extinctions. Those events removed roughly three-quarters or more of species. We are not there.

The finding in the literature is conditional: if current rates continue, that threshold is reached on a timescale of centuries. That is a projection with an if in front of it, and the if is the entire point.

Which is exactly why lesson 8.4 ended on curves that bend. The projection is not a prophecy. It is a description of what happens if nothing changes, offered so that something can.

What this chapter has actually been about

Five lessons, and one shape underneath all of them.

Lesson 8.1: two biological worlds collided and the exchange remade every continent’s food supply, while disease removed most of the population of one hemisphere.

Lesson 8.2: a procedure for testing claims was assembled from four continents and made binding, and knowledge started to accumulate instead of resetting.

Lesson 8.3: a stock of buried sunlight replaced an annual flow, the ceiling on energy came off, and one region industrialised while another was deindustrialised.

Lesson 8.4: after 1950 everything steepened at once, with real gains — food, medicine, life expectancy — bought against stocks that are not being replaced.

Lesson 8.5: the mark is in the sediment, and the argument about what to call it is smaller than the mark.

The common thread is acceleration bought on credit, and a species that got very good at drawing down stocks before it got good at noticing it was doing so.

The last chapter of this course asks what happens next. It will apply the same rule as every chapter before it: say what is measured, say what is modelled, say what is guessed, and never let those three blur together — least of all when the subject is the future, where the temptation is greatest.

Deeper

What a GSSP is and why it is demanding

A Global Boundary Stratotype Section and Point is a physical marker, driven into a specific outcrop or core, that defines the base of a time unit for the entire planet. The requirements are strict: the section must be continuous across the boundary, contain a primary correlation marker identifiable worldwide, have secondary markers, be accessible and protected, and be unlikely to be destroyed. Crawford Lake was chosen because it is meromictic — its deep water does not mix with the surface — so its sediments are undisturbed and laid down as annual varves, giving year-level resolution and a clear plutonium signal. The site is scientifically excellent. What the vote rejected was the case for creating the unit at all, not the quality of the section.

Why plutonium works and carbon-14 works differently

Plutonium-239 has a half-life of about 24,100 years and effectively no natural terrestrial source, so its presence in a sediment layer is unambiguous and will remain detectable for tens of thousands of years. Bomb radiocarbon is a different kind of marker: atmospheric testing roughly doubled the ¹⁴C content of the atmosphere, and the subsequent decline as that carbon was taken up by oceans and biosphere produced a curve that dates recent material to within a year or two. Its usefulness is temporary — the excess is being drawn down — whereas the plutonium is a permanent horizon.

The Holocene truncation problem

The Holocene has its own GSSP, in a Greenland ice core, and was subdivided in 2018 into three ages. Inserting an Anthropocene epoch at 1952 does not just add a unit; it terminates the Holocene and orphans the upper part of its youngest age. Stratigraphers who opposed formalisation argued that this is a large disruption to a functioning classification in exchange for a unit that is, at present, thinner than the sampling interval of most sedimentary records.

How extinction rate estimates are made

Background rates come from the fossil record, usually expressed as extinctions per million species-years, and are themselves uncertain because the fossil record is biased toward marine, mineralised, widespread taxa. Modern rates are estimated from documented extinctions of well-studied groups, principally vertebrates, extrapolated with corrections for undocumented losses. Ceballos and colleagues deliberately used conservative assumptions in order to argue that even a generous background rate leaves the modern rate far higher. Barnosky and colleagues compared cumulative losses against the magnitude criterion for mass extinction and concluded the threshold has not been crossed. These are compatible findings: a very high rate that has not yet run long enough to produce mass-extinction magnitude.

Frontier

Whether the event framing will be formalised

Treating the Anthropocene as an event does not require ratification in the way an epoch does, and the term is already in wide use across the sciences and beyond. Whether a formal proposal returns in some other shape is open, and the working group’s own position is contested.

What the boundary will look like in ten million years

Sedimentologists studying analogous past intervals expect the mid-twentieth-century horizon to survive as a thin, sharply defined layer with a distinctive geochemical and technofossil assemblage, in the way that the Cretaceous-Palaeogene iridium layer of lesson 5.7 survives. What is not known is how much of the current biosphere’s signature will be preserved, since preservation is strongly biased and most of the present will not fossilise.

Transcript and shot list

Target runtime about 9 minutes. Built as verdict first, then the evidence that lost, then the distinction that explains why both can be right. Shot types: ANIM is rendered from code with Manim, AI is a generated shot from Higgsfield with the shared style reference, REAL is agency imagery with credit, CAM is the narrator.

[00:00] S01 · CAM · Narrator direct to camera.

You have probably heard that we live in the Anthropocene, the age of humans. We do not. Not formally. In March 2024 the proposal to add it to the geological timescale was voted down, and the rejection was confirmed by the body that ratifies these things.

[00:20] S02 · ANIM · The proposal’s progress: working group from 2009, a vote in favour, a candidate golden spike selected in Ontario. Then the parent subcommission voting it down; the IUGS confirming; a procedural dispute noted in the margin.

It had got a long way. A working group running since 2009. A vote in favour of a formal epoch. A candidate golden spike chosen: a small, deep, exceptionally still lake in Ontario that lays down clean annual layers. Papers written, case made. The parent subcommission voted it down, and the rejection was confirmed. Some members of the working group disputed the procedure, and that dispute got reported alongside the result. So formally, we still live in the Holocene, as we have since the last glaciation ended.

[00:55] S03 · CAM · Narrator direct to camera.

And here is the sentence this whole lesson exists for. Not one piece of the underlying evidence changed. Sit with that combination, because it is a clean example of something this course keeps coming back to. Evidence and classification are different things. A vote can change what we call something. It cannot change what is in the sediment.

[01:20] S04 · ANIM · A sediment core rising through frame, with the mid-twentieth-century horizon marked. Each marker will be added to this core as the section proceeds.

So let us look at what is in the sediment, because the stratigraphic case is strong and it does not depend on the vote.

[01:35] S05 · ANIM · Atmospheric testing 1952 to 1963; plutonium-239 and doubled radiocarbon spreading through the whole atmosphere and falling out worldwide within a few years; the signal appearing in cores from the Arctic to Antarctica.

Between 1952 and 1963, atmospheric thermonuclear testing put plutonium-239 and a doubled radiocarbon signal into the entire atmosphere. It came down everywhere, within a few years, and it is in sediments and ice from the Arctic to Antarctica.

[02:00] S06 · ANIM · Why it is close to ideal: no natural source for Pu-239; sharp rise; dated peak; sharp decline after the 1963 test-ban treaty; a 24,100-year half-life keeping it readable.

For stratigraphy that is close to ideal. Plutonium-239 has effectively no natural source on Earth, so finding it means one thing. The rise is sharp, the peak is dated, and after the 1963 test-ban treaty the decline is just as sharp. It is the most globally synchronous marker in recent sediments, and with a half-life of twenty-four thousand years it will stay readable for a very long time.

[02:30] S07 · ANIM · Fly ash spherules from high-temperature combustion; then technofossils: concrete, aluminium in metallic form, glass, and plastics reaching deep-sea and polar sediments.

Then fly ash: spherical carbonaceous particles from high-temperature fossil fuel combustion, spread globally by the atmosphere and geologically distinctive. Then technofossils. Concrete, of which we have now made enough to cover a serious fraction of the planet’s surface. Aluminium, which essentially does not occur as a metal in nature. Glass. And plastics, which are geologically novel, are already in deep-sea and polar sediments, and do not degrade on any timescale that matters here.

[03:05] S08 · ANIM · Haber-Bosch nitrogen isotopes appearing in remote lake sediments. Then the domestic chicken: skeleton diverging from wild ancestor, deposited in enormous quantity, drawn as a future fossil horizon.

Lesson 8.4’s Haber-Bosch reaction has an isotopic signature, and it turns up in the sediments of remote lakes that never saw a bag of fertiliser. And fossils. The domestic chicken is now the most numerous bird on Earth by an enormous margin, its skeleton is unlike any wild ancestor’s after decades of breeding, and the bones are being deposited in vast quantities. Future palaeontologists will find a chicken horizon.

[03:40] S09 · ANIM · Three reasons for rejection, listed and weighed: seventy years against epochs of hundreds of thousands; the Holocene truncated at 1952 and its youngest age orphaned; and human impact spread unevenly across millennia rather than starting at once.

So why was it rejected? Three reasons, and only the third is really about the science. First, it is very short. Epochs run hundreds of thousands to millions of years. This one would be about seventy, sitting inside a Holocene that is only about eleven thousand seven hundred years old. Second, formalising it ends the Holocene in 1952, which is a big change to a well-established unit on the basis of a very thin sliver of section. Third, and this is the strongest argument: human impact is not synchronous. Farming began at different times in different places over thousands of years, as chapter 7 showed. Deforestation, extinction and land conversion are spread across millennia. Picking one global base date makes a long uneven process look like an instant.

[04:25] S10 · ANIM · The Great Oxidation Event and the Cambrian Explosion recalled from chapter 5, both labelled EVENT and neither an epoch. Then the definitions set side by side: an event as a described happening with duration; an epoch as an administrative container with a defined base.

Which brings us to the bit that gets misreported constantly. The alternative on the table is that the Anthropocene is a geological event rather than an epoch. And an event is not a demotion. Lesson 5.4 was the Great Oxidation Event. Not an epoch. No golden spike. One of the most consequential things that ever happened to this planet, and nobody thinks calling it an event makes it small. The Cambrian Explosion is the same. An event is a described happening with a duration and consequences. An epoch is an administrative container with a defined base, used for correlating rocks between continents. Calling the Anthropocene an event says it is real, global and consequential, and that it does not have one clean starting line. Which, on the evidence, is true.

[05:15] S11 · ANIM · Two candidate dates side by side. 1610: the Antarctic ice CO₂ dip, American depopulation, farmland reverting to forest. 1964: the bomb spike. The same period, two different stories about what it is.

And the choice of start date is not a neutral technical matter. Two were on the table. 1610, where Antarctic ice records a dip in carbon dioxide that one explanation ties to the American depopulation of lesson 8.1 — tens of millions of deaths, farmland going back to forest, that regrowth pulling carbon out of the air. The attribution is debated. Or 1964, the bomb spike. Choose 1610 and the Anthropocene begins with colonialism and a demographic catastrophe. Choose 1964 and it begins with nuclear and industrial modernity, and responsibility looks more recent and more distributed. Both are defensible stratigraphically. They tell different stories about who did this. Where a boundary gets drawn usually encodes an argument, and it is always worth asking whose.

[06:05] S12 · ANIM · Extinction rates far above background, with the estimation uncertainty shown as a band. Then the five mass extinctions at roughly three-quarters of species, and the current documented losses drawn well below that line, with a dotted projection reaching it in centuries if rates hold.

The extinction evidence gets overstated in both directions, so here it is with the uncertainty attached. Current extinction rates are estimated to be far above the background rate from the fossil record. Different methods give different multipliers. But the losses documented so far have not reached the magnitude of the five great mass extinctions, which removed three-quarters of species or more. We are not there. What the literature actually says is conditional: if current rates continue, that threshold arrives on a timescale of centuries. That is a projection with an if in front of it, and the if is the entire point.

[06:50] S13 · CAM · Narrator direct to camera.

Which is exactly why the last lesson ended on curves that bend. A projection is not a prophecy. It is a description of what happens if nothing changes, and it is published so that something can.

[07:10] S14 · ANIM · The five lessons of chapter 8 assembling into one shape: two biological worlds colliding; a method made binding; a stock replacing a flow; everything steepening at once; the mark left in the sediment.

So what has this chapter been about? Two biological worlds collided and remade every continent’s food supply, while disease removed most of the population of one hemisphere. A procedure for testing claims was assembled from four continents and made binding, so knowledge accumulated instead of resetting. A stock of buried sunlight replaced an annual flow, the energy ceiling came off, and one region industrialised while another was deindustrialised. After 1950 everything steepened at once, with real gains in food and medicine and life expectancy bought against stocks that are not being replaced. And the mark is in the sediment, whatever the committee decided to call it.

[07:55] S15 · CAM · Narrator direct to camera.

The thread running through all five is acceleration bought on credit. A species that got very good at drawing down stocks well before it got good at noticing it was doing it.

[08:15] S16 · ANIM · The course’s confidence labels — measured, modelled, guessed — held apart and never blurred; then the calendar returns and runs forward past the present into blank space.

The last chapter asks what happens next. It uses the same rule as every chapter before it: say what is measured, say what is modelled, say what is guessed, and never let those three blur into each other. That rule matters most when the subject is the future, because that is where the temptation to blur them is strongest. Chapter nine.

Shot list

Zero AI shots, twelve code-rendered shots, four narrator shots. The chapter closer is deliberately the most direct-to-camera lesson in the course so far.