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Hundreds of thousands of years in the future, when even the pyramids have been ground to dust by wind, one human structure on Earth will remain.

At least that’s the plan for Onkalo, a facility under construction right now in Finland. If successful, it may be one of the final artefacts of human civilisation.

If we look back at history, any attempt at building something so long-lived usually had religion in mind. Why else, if not for the Gods, would we build something to outlive us so many times over?

But Onkalo’s purpose is much more mundane.

It’s the world’s first permanent nuclear waste storage site. This is surprising for a couple of reasons.

First, why is it so important to build a storage site that will probably outlive civilisation?

Second, how can it be the first permanent nuclear waste storage site? Haven’t we been using nuclear power for decades?

Let’s jump in and find out.

The entrance to Onkalo, which will be cemented over in 2120 and hidden.

The amount of effort that’s going into Onkalo tells us something about the unique time we live in.

Specifically, about our waste.

We produce a lot of waste. All together we make 2.6 trillion pounds of it each year, which weighs more than 7,000 Empire State Buildings. By 2050, there will be more plastic by pound in the oceans than fish.

The trash skyscrapers in Wall-E are not far from reality.

It’s a sad truth that waste is one of our most enduring effects on the planet, and as our technology and standard of living improve, the more we seem to produce.

But of all our waste, the nuclear kind is by far the worst.

One type is called ‘plutonium-239’, and it’s produced in many nuclear plants. One thousand tons of it is currently in storage, with twenty tons being added each year as they operate.

Nuclear power has many advantages, but its creation of plutonium-239 is not one of them.

Accidentally inhaling just one-millionth of a gram of plutonium-239 dust will give you cancer. A pound of it is enough to kill 2 million people.

Once it’s been made, it takes over one hundred thousand years to degrade.

A ring of plutonium.

I want to spend a moment on why nuclear waste like plutonium is dangerous.

Fundamentally it’s an atom that’s unstable.

Either it’s too big, or has an unbalanced ratio of protons to neutrons. The atoms ‘decay’ which means they break apart, throwing off protons, neutrons, and other forms of radiation until their atoms are small enough to be stable again.

This can take anywhere from seconds to millions of years.

The gas being pumped in is Radon 220, and it’s radioactive. The radiation reacts with the liquid solution, allowing us to see it.

Although it’s possible for some radioactive substances to occur naturally, most of it on Earth is man-made. We make it as a byproduct of nuclear fission, where we break apart atoms to access the energy inside and use it for electricity and bombs.

A nuclear bomb test.

This radiation is so intense that it will kill our cells, or alter their internal molecules.

One of the first researchers into radioactivity was Marie Curie, the first woman to ever receive a Nobel prize. Unfortunately, she didn’t realise that while she was working her radioactive materials were killing irreplaceable cells inside her bone marrow, which stopped her body’s ability to make blood, which ultimately killed her.

Nowadays we have a much better understanding of what radiation can do, and are much more careful. Marie Curie’s notebooks (which are still radioactive) are stored within a dense, lead-lined box.

Radiation can also directly alter our DNA. If it hits the wrong spot, it can change the DNA’s instructions of when a cell should start and stop replicating, and the cell may start replicating out of control. It will replicate again and again, with every new cell inheriting the same faulty instructions. Before long, it makes a dense clump called a tumour, which (in some cases) can break apart and form new tumours around the body. If you hadn’t guessed, this disease is cancer.

It’s worth mentioning that not all types of radiation are bad. They’re often used in medicine to diagnose internal problems. But these are different types of radiation that are much lower energy and do not damage the body. A doctor is unlikely to use plutonium to diagnose our broken bones.

So what do we do with a substance that is so toxic, yet lives for so long? 100,000 years is a really long time.

For some perspective, the pyramids are ‘just’ 5,000 years old.

100,000 years ago, Homo Sapiens had not yet left Africa, and the area around the Onkalo facility was inhabited by an entirely separate species of human, Homo Neanderthalensis.

The world 100,000 years ago also contained woolly mammoths, woolly rhinoceroses, and cave lions.

Who knows what it will look like after another 100,000 years.

What do we do with a substance (that we already have a thousand tons of) that remains toxic on timescales so far into the future that by then humans might have split into new species?

For the most part, the answer is we don’t know.

All of the nuclear waste that has ever been produced, including plutonium, is currently in temporary storage until a permanent solution is found. Many temporary storage facilities are not designed to last more than thirty years, and many of them are nearing or have past their expiration date.

All, that is, except the nuclear waste created by Finland, which is the only country to create the world’s first permanent nuclear waste storage facility. Onkalo.

The plan is to bury it deep within the Earth, where there is no geologic activity, where not even the glaciers of another Ice Age in the distant future can disturb the waste.

Onkalo’s blueprint.

The main wildcard that could disturb the site is future human beings (or the species that comes after homo sapiens).

Because the signs of Onkalo will still be visible on the surface even far into the future, the Finnish government has determined that a message has to be left for these people. We have to warn them to stay away, but without making them even more curious. Not an easy task when our language is certain to be unrecognisable to them.

A few ideas have been proposed.

One idea was to build a forbidding landscape of concrete spikes, to create the impression that the area is forbidding and dangerous.

Another was to genetically engineer a species of cats to glow when radiation is present, and release them in the area. Hopefully, people would be frightened of the strange animals and stay away.

But even these may end up as strange attractions to future people, and invite further exploration.

While how to express a message across a hundred thousand years of changing languages and cultural norms remains a difficult problem, we do have a good idea on what the message should say.

Academics at Sandia National Laboratories composed this chilling message for the people of the distant future. It reads:

This place is not a place of honor… no highly esteemed deed is commemorated here… nothing valued is here.
What is here is dangerous and repulsive to us. This message is a warning about danger.
The danger is still present, in your time, as it was in ours.
The danger is to the body, and it can kill.
The form of the danger is an emanation of energy.
The danger is unleashed only if you substantially disturb this place physically.
This place is best shunned and left uninhabited.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.