Open to the general public, Science en direct is an entertaining, free event organised by 16 French research organisations designed to arouse people's curiosity about science.
Presentation: Technosoils: how to make new soils
Welcome to this encounter live from the Cité des Sciences et de l'Industrie. As we'll be discussing soils, here's some important information. Did you know that to create just 5 centimetres of fertile soil, it takes about 500 years in a natural state? That's from a very serious study carried out by scientists. Sadly, it takes us a lot less time to degrade these soils through erosion, overexploitation in farming and urbanization. But the good news today is, scientists are working on creating new soils called technosoils, which are totally artificial, from recycled waste. This is also part of the circular economy. To talk about technosoils, I'm delighted to greet Philippe Bataillard. Hello, Philippe. You're a geochemist at the BRGM: the French Geological and Mining Research Bureau. To get us started on these famous technosoils we'll be discussing, the aim is not to use them in the country but in urban areas.
Exactly. We want to preserve the soils in the countryside by fabricating soils in cities.
OK. So it's a question of greening cities?
We have degraded urban soils so much that vegetation won't be able to grow again without a push-start. If we want vegetation to grow again on wasteland, such as an old industrial site, we think about bringing in new soil, constructing a soil which is immediately fertile.
I guess demand is growing fast in urban areas because the trend now is to green by creating parks, planting trees...
It depends on the city. Some are under more pressure than others. But large metropolises like Paris and Lyon are more and more interested in this.
The way you make the soils is quite original. We'll take the materials one by one. To start with, you use materials that are already in the cities.
Inert matter, notably mineral. We don't want materials to travel. Once they're in a truck, they consume fuel and pollute.
They create CO2.
So we aim to use a maximum of materials already in a city, notably from demolished buildings. When you demolish a building, the bricks from the old walls are broken up. These produce what we call "fine-grain", an inert mineral matter
which we put in the soil.
So you demolish a building in concrete or bricks and you recover the materials?
Yes. First of all, we get rid of any undesirable materials, like asbestos, for example. So we remove all the asbestos, wood, glass and plaster from the building, until only the mineral matter is left: concrete, bricks... Once this is ground down...
Reduced into powder?
Some. But there are several grades.
Coarse grade is already used in geotechnics, such as road construction. But some of the material is also ground down into powders. Sadly, for now, we don't have a specific use for it, because it has few geotechnical properties.
What are "geotechnical properties"?
A coarser material bears more weight. You can roll it once it's spread out. It's hard to pack fine-grain.
We have some samples. Don't turn it too much, for the camera's sake.
That's powdered what?
We demolished a building, ground the materials and retrieved the fine-grain. Fine-grain refers to the finesse of the powder. This is from a 4-millimetre sieve.
It's from concrete?
Mostly concrete and brick. It's what gives it the salmon-pink tinge. Red bricks.
Our cooking lesson continues with something quite extraordinary! Don't be surprised. Maybe the camera can pick it up. It's called "street". Why "street"?
In fact, it's a material that we... retrieve from street cleaning.
It's street dirt?
Isn't it filthy?
That's a presumption. The original waste contained plastic bottles, drinks cans, cigarette ends... That's all easy to remove. You pass the waste through a sieve and you're left with the fine material. And when you analyze it, it's actually fairly clean. I say "fairly", because it's still urban matter.
It's the trash picked up by street-sweeping trucks? You pick up all the trash and dust and you sift it?
Right. There are particles carried by the wind, clays, dust, construction dust, organic materials, such as dead leaves, and, sadly, bits of tyre and eroding cars. Material typical of a city, marked by the city's contaminants in acceptable proportions for an urban environment.
We hope you're right, because we may use technosoils for urban kitchen gardens. It's guaranteed 100% de-polluted?
The day we manage to do that, we'll guarantee it's totally risk-free.
For now, we have a totally inert raw material, in which it's impossible to grow plants. To that, we have to add something living.
What's in front of you.
We mentioned this mineral matter, which is organic matter, but not only that. The mineral matter and the organic matter must combine to make a very fine aggregation between the mineral and the organic. But we'll come back to that. The idea is to find materials that form the chemical composition of soil. For that, you need organic matter. The "street" substances are interesting because they're very organic. They're also very fertile because they contain phosphorous. Fertile means it contains nutriments that help plants to grow.
You can also add compost.
Ground up vegetal waste?
That, composted household waste...
Yes. We exclude no sources of organic materials. I have highly experienced colleagues, notably at the University of Lorraine, who have shown that in paper-mill sludge, what's left over from recycling paper, there's always a fraction of it
composed of vegetal fiber too fine to make paper or cardboard.
But before, there was ink.
Yes. And that ink contained contaminants, notably heavy metals. Luckily, we now have fewer contaminants in ink, if any at all. We have water-based inks, without contaminants. So fine-grains are interesting as they're organic and, in general, another ingredient is added: limestone, which is also very good for soil.
So you make tailor-made soils. We won't give you the recipe, as it's complicated. But you have the main ingredients. So these soils become fertile very rapidly?
What does that mean exactly?
Once you mix all the materials, you can lay them on the site you want to green. Then you can plant plants that will grow in the correct manner.
As well as in natural fertile soils?
Yes, just as well.
Just as well?! I guess you must choose species according to the soils. Because you have different mixes.
We can even create tailor-made soils. For example, a developer might ask us for an acidic soil because he wants plants that like acidic soils. So we find the materials with those properties. We can create an organic soil for plants that need a lot of humus. We can create a poor soil which helps to drain off water. So we're able to make kind of tailor-made soils. "Kind of", because we're restricted to materials produced by cities.
You are scientists always in the vanguard of research. We're in a circular economy with the recycling of waste. Does that meet the demand of cities? I know that some cities no longer want to import soils from the country.
Right. Of course, there's Greater Lyon...
Lyon decided to stop bringing in soil from the country.
Indeed, although we don't know who was first. Now they know vegetal soils can be made, they want to invest in that process to preserve soils in the surrounding countryside. I didn't mention this, but vegetal soils used in cities come from cities encroaching on the countryside.
Cities are growing. We're probably urbanizing too much.
We lose a lot of countryside every decade.
Absolutely. The idea now is to find an alternative, because while we need vegetal soil and the resource is available, why look elsewhere? But to fight against this artificialization, if we can offer man-made vegetal soils, we add strength to the argument: "No need to urbanize".
Can we imagine that tomorrow, a city-dweller owning a plot of infertile land might turn to technosoils?
It's possible. For the moment, we're still in the demonstration phase. The sites that are available are former industrial sites that are slightly damaged. So they're systems marked by the influence of man. So the day we want to grow edibles on these soils, they must be free of all undesirables. But it is certainly possible.
For now, this is just research carried out by the BRGM, in the public interest, and you need partners to develop all this.
Exactly. Regarding soils, each researcher tends to have his own definition. A geotechnician is mainly interested in the surface. Can he build on it? For an agronomist, it's the ability of a plant to grow on it. An archeologist wants an archive of the soil. We tend to speak more about function than the soil itself. When you construct a soil, you touch on all these areas. So ours is a project made for working with partners. An example is the SITERRE project, a project that allows me to do this, involves ten partners. Agronomists, professionals from public works construction... And so on. I can't cite them all...
Thank you very much, Philippe Bataillard. Well done for all your research. So that was: the BRGM, now working on technosoils.
"Mystery object" with Pierre Pannet and Thomas Jacob
Their names are Pierre Pannet and Thomas Jacob. I won't tell you what they do in life, as you'll have too many clues. They're here with an object that turns. Pierre is holding it. And Thomas has a big box on the floor, on a support, a bit strange with 3 legs. Any ideas from the audience?
Maybe an hourglass.
Hang on, we can't hear. Do I have another mike for Thomas? No? OK, you'll share it then.
It's not an hourglass.
Not an hourglass. Do we start...
Hold on, there are some questions.
Did it come from space?
Is it from outer space?
We'll try to give you some context... Go ahead.
To listen to sounds?
To listen to sounds...
OK, we'll try to give the audience some context. When you use these objects, what do you do?
I take measurements over regular distances. For example, every 3 or 5 metres.
Hang on, you're saying too many things.
You take this box?
Yes. I set it straight, and then... I press the button.
You do that in the countryside?
Town or country. Wherever we like!
Can I do it here?
Is it for observing space or the earth?
You could say it's for observing the earth.
What idea is going through your mind?
I'd say it's to observe the layers, the strata of the earth.
Good answer. We can observe that, but indirectly.
Oh, come on!
Hold on, hold on... This object is exactly what that girl said?
We can observe geology with what we measure using this object.
She didn't say that. She said, "Observe the layers..." Is that it?
The strata of the earth.
Is she right? Can we applaud her answer?
It's the right answer.
For this object. Good job!
She was very fast! I'm awestruck! I think you met these guys yesterday and now you're cheating! So you put this object on the ground and you can approximately measure the geological layers?
In fact, it gives an idea of the density of the layers. By density, I mean: Is it heavy or not? It's a clue: it does help to measure the density of the subsoil.
It gives some info about the subsoil, but we want something more precise. That's a half-right answer!
We still have some questions. What's it for exactly?
Could you show us what you do with your device?
I walk around.
What a fantastic job!
You put that down and you walk around?
Are you asked questions as you walk around?
I walk around in places where I meet few people.
I see. Places that are... deserted?
Deserted places... No, not deserted.
Is it to measure whether the earth is solid or liquid?
Give Thomas the mike, because he'll answer this question.
I didn't hear all of it.
For measuring earthquakes?
No, not earthquakes.
The question was: Do you measure whether the earth is solid or liquid?
We can measure whether the earth is heavy or not heavy under our feet. Whether the rock is very heavy
or slightly heavy.
Hold on... Another guess.
Is it to find something hidden underground, like ancient buried objects?
Maybe. We could.
If it's contained in...
You're saying too much! What could you look for underground that could interest - I'll tell you what they are now - one geophysicist and one geologist? I have three guesses... four!
Is it to find "sossils"?
To find fossils!
A bit of an answer!
Maybe you'll get it all together.
Is it used to observe the tectonic plates?
That can be done.
You're getting warmer, so you'll get it soon.
Is it for observing insects in the earth?
We'll give you a clue to help you get it quicker.
We're all ears.
Pierre... tell us where you go with your object. Why don't you meet people when you're walking around?
Because I go down into the depths of the earth.
Ah, there's a hand up!
It's to find his way around underground caves.
Which of them?
The guy on the left?
Is it a map for caves?
It helps me make maps of caves.
Maps of caves?
Yes, very precise ones.
An excellent answer.
A correct answer!
What's your name?
Loïc found the right answer!
Can you tell us what this object is called?
And your object is?
A ZEB-REVO. It's a 3D laser scanner.
You have 3 minutes to tell us how you use these two objects together.
The gravimeter measures spatial variations in the earth's field of gravity. That's what stops us from flying off the planet. It's what pulls our bodies towards the centre of the earth. And this field of gravity is linked to the distribution of density in the subsoil.
The heavier the matter is under our feet, the stronger the field of gravity. The lighter it is, like in ground with cavities,
the weaker the field of gravity is. So this instrument finds places where the field of gravity is either weak or strong. Then we can produce a map by taking regularly-spaced measurements every 5 or 10 metres. And can identify areas
with mass anomalies in the subsoil.
A question: If I'm standing above an underground cave, I'm lighter because I'm pulled less towards the earth?
By how many kilos?
Not kilos, but metres per second squared.
It's an attraction, an acceleration. But we're talking billionths. So a tiny variation.
I can't feel it, but this does.
It knows there's a hole down there!
And once it finds a hole, you go down in it?
Since the dawn of time, man has constructed by extracting stone then building over the hole. These days we have to be careful the ground doesn't cave in. So I need Thomas and his magic device to find the holes. Then we dig so I can go down, and with my device, I precisely map all the underground holes. They could be former quarries, like in Paris,
or natural caves.
Here are some photos.
There you go, excellent! We go down into underground environments like that, which are sometimes in ruins. Our aim, with this device, is to monitor these underground spaces to see if it's dangerous for you when you're walking down the street.
Thank you, Pierre Pannet and Thomas Jacob, for your ZEB-REVO and gravimeter. And well done to you
for finding the answer so quickly! It's really impressive! It's always the kids, and they're very fast!
Presentation: "Rising sea level and coastal flooding"
Welcome to this first encounter which will plunge us into an ocean which keeps rising all across the world, by submerging islands, coasts, and even our shores. Added to that, sadly, as we have seen, are increasingly violent
storms and cyclones. All due, of course, to anthropogenic global warming. Which means caused by human activity. I'm delighted to introduce Gonéri Le Cozannet.
You're with the BRGM: the Geological & Mining Research Bureau. You're a researcher in the Risk & Prevention Department. Is that right?
Let's dive right in. You agree, no doubt about it, the oceans are rising?
No doubt, the oceans are rising. They have risen 15 to 20 cm since the mid-19th century. You brought along a diagram for us to see.
Here it is.
Exactly. It shows observations between 1870 and 2000. The 15 to 20 cm I mentioned. And the predictions of two scenarios. In the first, we severely cut greenhouse-gas emissions.
In the second, we do nothing.
We continue emitting greenhouse gases. That's the red.
And that would be totally catastrophic. The oceans are rising, and there's often talk of 2100. As if they'll stop rising in 2100 if we do nothing!
We know they're rising, and we know why. Due to the thermal expansion of the oceans, the melting glaciers...
Whoa there! We understand the melting glaciers, but you used a long term before that.
I'm sorry. The thermal expansion of the oceans.
And what's that?
The oceans are heating up and dilating. That explains half of what we saw in the 20th century.
The oceans are rising because temperatures are higher. The ocean surface is notably much warmer and so it's swelling. Like when you boil water.
Climate change is an energy imbalance in the earth's system. 93% of additional warmth due to climate change goes into the oceans, which absorb it and swell.
OK, but if we look way back into the past... You brought another diagram on this. We know the oceans have risen,
because a long time ago, they were very low. Then things stabilized, before starting to rise again.
21,000 years ago, there was an ice age. There were four major ice sheets. One over Scandinavia, one over Canada, one over Greenland, and one over Antarctica. These ice sheets melted, and 6,000 years ago, the ocean level reached its current height. The ice sheets were 120 metres thick, so you could walk from France to England! Or 200 km from Nantes before you saw the sea! Currently, we're in a fairly warm interglacial period. Since 1870, after being stable for 6,000 years, the ocean level has been rising due to climate change linked to the greenhouse effect.
Clearly due to emissions of greenhouse gases.
No doubt at all. There's scientific consensus on the rising ocean level. It's one of the most integrated ways of observing climate change. The earth's energy imbalance is difficult to observe. But the rising ocean level is a variable
which you can observe and which embodies this imbalance.
Something that allows us...
To observe easily and reconstruct this imbalance.
Absolutely. So it's fact. To sum up, we have the dilatation of water, melting glaciers, along with the melting of the poles... Added to that, sadly, as we've seen in recent years, depressions bringing monster storms which in turn bring more and more water to our shores.
Two things make us think there are more storms. Firstly, we see them more easily, because there are more assets along the coasts. We know there are more storms because there's more damage. The second thing is the rising sea level, which has caused an increase in extreme episodes. Added to storm cycles, which haven't changed much in 100 years, is the rising sea level. We characterize storms by their return periods, like centennial storms
which occur every 100 years, decennial storms, every 10 years... There's generally only a 40-cm difference between them.
At the BRGM, you model these storms to see how far inland they go. We have a very interesting animation to watch.
We all recall 2010 and Cyclone Xynthia, and the ensuing disaster. But this is an animation of Storm Johanna. It was in March 2008. It submerged the Gâvres Peninsula in the Morbihan in Brittany.
That's right. Here you can see the incoming tide. The tide is oncoming, the storm is causing a fall in atmospheric pressure, the sea level is rising, and the wind is forcing water sideways.
All very quickly?
Yes. We modelled each wave and we see a complex flooding process.
It's just starting...
It's not a static water level going over the defences. Each wave is going over them. So for the overall model, we had to model each wave. And there, very quickly, the peninsula is flooded. Evidence of this remains with water-level marks
on the walls. There were no victims, but lots of damage. So the traces on the walls validate our model. It allows us to formulate coastal risk-prevention plans so we can reduce the risks across the area.
That's the aim of the work in your department at BRGM: to establish prevention plans. We just saw, very clearly, how France's coasts can be suddenly assailed by the ocean and be totally flooded. What are the most vulnerable areas along the coasts of mainland France?
It's the very low coastal areas that are floodable. Along with erodible areas. For example, in Aquitaine, some sandy beaches are eroding by 1 metre a year. If there are homes and businesses behind the beach, we're gradually reaching a situation where we either move the buildings or protect them with breakwaters or riprap, for example. Other low coastal areas in France are Languedoc-Roussillon, Poitou-Charentes... All over, really.
More than we imagine.
All along the coasts, not only in big regions, but well identified, are flood-risk zones. They're in Brittany, everywhere.
The Camargue is often mentioned, but there's Aquitaine, Brittany, Charente...
The Giens Peninsula...
So global warming and the rising ocean level are of great concern to us. A final word on French overseas territories. Notably Guadeloupe, which is a very fragile zone.
The problem with Guadeloupe is a low area called Jarry, where 40,000 people work every day.
Exactly. It's a crucial area for Guadeloupe's economy, and it's only 40 cm above sea level. So imagine if the ocean were to rise 40 cm. Well, this is expected to happen by the second half of the 21st century.
So there will be problems.
Big problems. Problems, too, for French Polynesia, and the Tuamotu Islands. So the harsh realities are being placed in front of our eyes through your studies.
We're at a moment where the sea level is starting to accelerate. The question is: how fast? Today, it's 3 mm a year. 1 cm a year is possible during the 21st century. It depends on our greenhouse gas emissions. Thank you, Gonéri.