There Have Been
So Many Earths

Some of the bumps were upside down

contested

This is the spread where we decline to take the video's word for it, and we are naming that rather than doing it quietly.

The source list behind the talk cites Nutman et al. (Nature, 2016), which reported 3.7-billion-year-old stromatolites — layered mats built by microbial communities — in the Isua supracrustal belt in Greenland. If it holds, it pushes life back by 200 million years and is one of the most important observations ever made.

In 2018, Allwood et al. went back to the same rocks and published in the same journal. Three-dimensional analysis of the structures' shape and orientation, plus trace-element chemistry, pointed the other way: these look more like deformation features formed long after burial, in metasediments squeezed and altered by heat and pressure. The detail that sticks is the plainest one. Some of the bumps point downward. Stromatolites grow up, toward the light. They do not grow down into the mud.

The oldest evidence for life that the field broadly accepts is younger and further south: the 3.48-billion-year-old Dresser Formation in the Pilbara of Western Australia, where stromatolites, microfossils, and fractionated carbon and sulfur isotopes agree with each other. Even that has had challengers arguing some of its structures are volcanogenic look-alikes.

The invention, and then a billion years of nothing much

documented

This is the hinge of the whole piece, and it is the one thing on the list that is neither a rock nor an accident. Somewhere in the Archean, in an ancestor of the cyanobacteria, a protein complex learned to pull electrons out of water.

Photosystem II. A cluster of four manganese atoms, one calcium and five oxygens, holding water still and taking it apart with sunlight. The waste product is oxygen. As far as the evidence goes it happened once — every oxygen-producing organism alive, cyanobacterium and redwood and kelp alike, inherited that one machine, the plants and algae acquiring it secondhand by swallowing a cyanobacterium and keeping it.

So: the single most consequential invention in the history of the planet's chemistry, arrived at once, never repeated, never improved on in any fundamental way.

And then the sky did not change for something like a billion years.

Not because the machine was broken. Because oxygen is greedy and the world was hungry for it. Dissolved iron took it. Volcanic gases took it. Rock surfaces took it. Every molecule the biosphere produced was consumed on contact by a planet with a very large appetite and no reason to stop. The geochemical record shows local, temporary whiffs — oxygen oases — hundreds of millions of years before anything global. Sinks filling, and filling, and filling.

Hold that number against the one everybody quotes about Chicxulub. A billion years, against thirty seconds. Both are on the same list of most important things that ever happened. Only one of them is a story.

Keep scrolling. There is a lot of this left, which is the point — you are falling through the wait, not through an error in the layout.

The sinks fill, and the air becomes a different substance

documented

The Great Oxidation Event is the moment the accounting flips: production finally exceeds consumption, and free oxygen accumulates in the atmosphere for the first time.

It is not gentle. For most of the life then alive, oxygen is a poison — a reactive gas that tears molecules apart. Whole ways of being alive are pushed into the mud and the deep water and the airless places, where their descendants still live. It is very likely the largest extinction event in the history of the planet, and it was caused by a metabolic by-product.

It also builds the ozone layer, which lets anything live on land at all, and it makes possible a way of getting energy from food that is roughly an order of magnitude better than the alternative. Everything with a body worth the name runs on that margin. You can still do it the old way — glycolysis, no oxygen required — and you do, briefly, every time you sprint. You do not die of holding your breath because you cannot make energy. You die because you cannot make enough.

Two things at once, then, and no way to separate them: the worst thing that ever happened to the biosphere, and the reason there is anything here to call it that.

A merger that was not a moment either

documented

An archaeon took in a bacterium and did not digest it. The bacterium became the mitochondrion. Everything with a nucleus — every animal, plant, fungus and protist, you and the yeast in your bread — descends from whatever cell that was.

The house has a whole zine on what this means, and it is not this one: No. 7, You Were Never One Thing, on the cell as a truce rather than a unit. What we want here is only the shape of the event, because the shape is the argument.

It was not an event. Green says so himself, and the literature agrees: a bunch of things happened in succession, not simultaneously. There is no surviving lineage of half-built eukaryotic cells to show us the order. The closest archaeal relatives we have found — the Asgard archaea — contribute most of the conserved eukaryotic machinery, with the bacterial partner contributing mainly the energy systems, which means the merger was not one swallow but a long negotiation whose minutes were not kept.

And the date is soft. Molecular clocks calibrated against fossils put the last common ancestor of all living eukaryotes somewhere around 1.84 billion years ago, with the crown group diversifying over the few hundred million years after. That is not a date. It is a neighbourhood.

Where the map begins, and why the earlier globes are blurred

contested

Every globe above this one is drawn faint and dashed, and this is the spread that owes you the reason.

The best continuous full-plate reconstruction of Earth — Merdith and colleagues, Earth-Science Reviews, 2021 — runs from 1 billion years ago to the present. That is not a shortage of effort. It is where the palaeomagnetic and geological constraints stop being able to hold a self-consistent model together. Before it, there are named supercontinents — Vaalbara, Ur, Kenorland, Nuna — and there are honest disagreements about whether some of them were supercontinents, what shape they were, and in one or two cases whether they happened.

So the drawings sharpen as they come forward, and that is not a style choice. A crisp coastline at 3.5 billion years would be an invention wearing a map's clothes. If we drew every globe with the same confident line, the picture would be making a claim the science does not support, and it would be making it more persuasively than any sentence could.

Even Rodinia, where the models start, is argued about. Pannotia, the proposed supercontinent between Rodinia and Pangea, may not have been one at all. We have not drawn it.

A continent is not a moment

documented

Cali Moore, who spent two years making a television series about it, said the thing that gives this spread its title. Most of us carry a picture in which all the continents came together, stood there for a bit, and then set off in different directions.

Over a hundred million years of being a continent. Longer than the entire history of primates, several times over. It changed shape while it was there. It was not a formation; it was a condition. And it was never a circle or a blob — it was roughly a C, curled around the Tethys ocean, which is a shape it is hard to unsee once someone tells you it looks like a Pac-Man.

Being one continent did things. The interior, around the equator, was desert — a barrier so effective that what lived in the north largely stayed north and what lived in the south stayed south. One landmass, and still two worlds.

And it took something away. In the Carboniferous, the wetlands were forested by lycopsids — club mosses, which today are small enough to kneel down to, and which then grew a hundred feet tall and spanned continents. When Pangea assembled it dried those wetlands out. The giant ones went. The small ones are still here.

We are going to leave that where it is for now and come back to it. It is very hard to hear only the ones who could shrink got through as a neutral fact about plants.

The breakup was not a moment either. Rift basins were opening by around 230 million years ago. The flood basalts of the Central Atlantic Magmatic Province came around 201 million years ago. Genuine separation took until roughly 175. A hundred and forty-five million years of assembly, tenure and divorce, and no single day you could put on a calendar.

Two of these bars cannot be drawn

Same scale for all five, linear, no tricks. The longest bar is the time from the eukaryotic common ancestor to now — call it 1,840 million years — and everything else is measured against it.

• Eukaryotes to now · ~1,840 million years
• Oxygenic photosynthesis to the sky changing · ~1,100 million years The gap between the invention and the consequence.
• Pangea, assembly to separation · ~145 million years The thing most of us picture as a moment.
• Theia, the impact itself · hours Drawn as a two-pixel line because at this scale it has no width. Honest value: about 0.0000000001%.
• Chicxulub, the decisive interval · seconds Same. The bar is a marker, not a measurement — there is nothing there to measure.

The two entries that cannot be drawn are the two that everybody can name. The two that fill the chart have no anniversary, no crater, no witness and no name that would fit on a poster.

The moments are memorable because they are shaped like stories. Beginning, middle, end; a protagonist; an interval short enough to imagine standing inside. The durations are shaped like weather. Nothing happens, and nothing happens, and then the thing that had been happening all along has happened.

Ask me when it started

Here is a question we get asked constantly, in clinics and at family dinners and in the first ten minutes of a job we have just disclosed at. When did you know? When were you diagnosed? What happened to you?

Every version of it assumes an impact. Something arrived, at an angle, on a date, and after it things were different. Give us the crater and we will understand you.

Mostly there is no crater. Mostly what happened to us is that a difference we had always had met an environment that had no room in it, slowly, over years, in a thousand encounters too small to itemise — and then one day there was a word for it, and the word arrived long after the thing it named. The diagnosis is not the event. It is the sinks finally filling.

And the accommodations that actually changed our lives were never moments either. Not the meeting where it was agreed. The two years afterwards in which nobody made us explain it again. A duration is what a support actually is.

So we will say what the chain says. You do not owe anyone a space rock. A life that cannot produce a single dramatic afternoon to account for itself is not an unexplained life. It is the ordinary case. It is what almost everything that ever mattered on this planet looked like from the inside.

And about the club mosses. When Pangea dried the wetlands out, the lycopsids that survived were the ones that could shrink. We are not going to pretend that reads as neutral. Fit through the gap or be a fossil is a description of the Carboniferous and also of a great many classrooms. The difference we insist on is that a drying wetland has no author and a classroom does. Nobody chose the desert at the centre of Pangea. Somebody chooses the one at the centre of an institution.

Four models of the next supercontinent, in 200 to 250 million years. They disagree about which ocean closes, so we have drawn all four and picked none. Earth has never held an arrangement, and it is not holding this one. There have been so many Earths. Every configuration was temporary, and so was every argument that any of them was normal.

What this chain refuses

• that the universe was aiming at us. Every link here could have failed, and the fact that none did is a thing we observe, not a thing we were promised.
• that contingency means meaninglessness. It could have gone otherwise and it went this way and here you are. Those three facts do not cancel.
• that early means easy. We are the only sample, and we could not have been drawn from anywhere else.
• that the dinosaurs were in the way. They were a hundred and sixty million years of somebody's life, and mammals did not deserve the room more.
• that a story is a measurement. Thirty seconds travels further than thirteen per cent because it is better shaped, not because it is better evidence.
• that a person owes anybody an origin story. There is no requirement to produce an impact to justify a difference.
• that only the shrinky ones survived is advice.

Sources

On the title

On the form

Credits

Love you down to your star stuff.