The traces we leave

Snow that fell on the high plateau of East Antarctica never melted. Year after year it was pressed into ice, and each layer closed over a little of the air above it, in bubbles too small to see.

At Vostok, one of the coldest places on the planet, a drill went down into that ice through the 1990s: Soviet then Russian drillers, French and American scientists, a thin cylinder brought up metre by metre, cut, labelled, flown away in cold boxes. In January 1998 the drill stopped at 3,623 metres, a little above a lake sealed beneath the ice.

In the coal country of the English Midlands, at the beginning of the eighteenth century, the deeper the miners dug, the more water rose to drown the seams. Horses turned pumps in endless circles, and it was not enough.

In 1712, near the walls of Dudley Castle, a new kind of machine was set to work. A fire boiled water in a boiler; the steam filled a tall cylinder; a spurt of cold water collapsed it, and the weight of the sky itself drove a piston down. A great wooden beam rocked above the pit, and water came up. The engine's maker, Thomas Newcomen, sold iron tools in a harbour town in Devon.

It looks like a large tricycle that has lost its rider. Two tall wheels at the back, a small one in front, a bench, a steering rod with a little handle. Behind the seat, a single cylinder, a flywheel lying flat, a few vessels of brass and copper.

In the winter of 1886 its maker, Carl Benz, registered it at the patent office as a vehicle driven by a gas engine. The engine was his; it burned light petrol bought at a pharmacy and gave less than the strength of one horse.

Nitrogen is most of the air this civilization breathed, and yet its fields went hungry for it. The gas would not combine with anything. For centuries, farmers returned it to the soil with manure and beans; later, ships carried seabird droppings from Peru and saltpetre from the Chilean desert.

In a laboratory in Karlsruhe, on 2 July 1909, a chemist named Fritz Haber and his young assistant showed visitors from a dye company a small steel apparatus. Gas went in under great pressure; from a narrow tube, clear drops of liquid ammonia fell, one after another. The assistant kept two sealed tubes of them.

It looks, at first, like a stone that has been badly cleaned. Then the eye finds the threads: green, blue, yellow, the fibres of rope and fishing net, sealed into a crust of sand and black volcanic grit.

Nobody made it. The plastic crossed the Pacific on its own, carried by the great slow turn of the currents, and came ashore on a remote beach at the southern end of Hawai'i with everything else the ocean had gathered. People camped there and lit fires. The plastic softened, flowed around the sand, the basalt, the shells and the coral, and set hard.

In the last weeks of 1998 a single cylinder rose from the steppe of Kazakhstan on a Russian rocket. Its name, Zarya, means dawn. Others followed, American, Russian, European, Japanese, with a Canadian arm to join them together, until a structure almost as long as a football field hung above the clouds.

Since November 2000 there have always been people inside it. They slept strapped to walls, grew plants, repaired leaks, looked down at the planet sixteen times a day. For a whole generation, not every human being was on the Earth.

Do not look for treasure here. Behind the door in the mountain there are only seeds, in plain boxes on metal shelves.

This civilization lived on plants its farmers had shaped over some ten thousand years, and it kept their varieties in genebanks scattered across the world. Genebanks burn, flood, run out of money, fall into wars. So in 2008 Norway opened a vault in the frozen mountain above Longyearbyen, far north on Svalbard, where any genebank could send a copy of its seeds for free and take it back whenever it needed.

This is a message this civilization knew it was sending.

On 2 February 2020 a company that hosted the code of millions of programmers froze a picture of all the active public projects in its care: operating systems and games, tools for scientists, the programs that ran websites and phones, the small experiments of students. Then it wrote them, not onto disks, but onto film.