Les scientifiques ont découvert quelque chose de véritablement effrayant caché au fond de l'océan Atlantique, digne d'un film de science-fiction. À des kilomètres sous la surface se trouve un immense « bassin de saumure », également connu sous le nom de « lac toxique ». Ce lac sous-marin est si salé et dense qu'il ne se mélange pas avec l'eau de mer environnante, créant son propre petit monde inquiétant. Ce qui est terrifiant ? Il est mortel pour la plupart de la vie marine — tout poisson ou créature qui y nage n'a aucune chance. Mais, de manière étrange, certains organismes uniques y prospèrent, s'adaptant à des conditions extrêmes qui pourraient nous aider à comprendre la survie sur d'autres planètes. C'est un rappel stupéfiant de combien de notre planète est encore inexplorée et pleine de surprises ! Animation créée par Sympa.
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FunTranscript
00:0066 million years ago, maybe in the month of September, a huge asteroid hit the Earth,
00:07sowing chaos and devastation.
00:10The tragic consequences of this terrifying collision have led to the extinction of dinosaurs.
00:15Yes, I want to talk about the asteroid of Chicxulub which left a huge crater in Mexico
00:20and changed life on Earth forever.
00:23Today, it turns out that this is not the only cosmic rock to have hit our planet at that time.
00:28Scientists have just confirmed the existence of another asteroid.
00:32This second asteroid was not as big as Chicxulub, but it still had a hell of an impact.
00:38It crashed off the coast of West Africa, sinking into the ocean and leaving behind a crater, the Nadir crater.
00:46And believe me, its effects are far from insignificant.
00:50The impact was so powerful that it triggered a real tsunami.
00:54These waves rose to more than 790 meters in height,
00:59almost the size of Burj Khalifa, the highest structure ever built by man.
01:04But how did we come to the conclusion that there had been a second impact?
01:09Wisden Nicholson, from the Eriot-Watt University, spotted the Nadir crater in 2022.
01:15Dr. Nicholson examined high-resolution images of the ocean floor
01:19when he noticed a huge depression 9 km wide under nearly 305 meters of water.
01:25He thought it could be an asteroid impact crater,
01:29but at the time, the evidence he had was not solid enough.
01:34Today, scientists have confirmed that it was indeed a crater.
01:38A second asteroid did indeed hit Earth at the time of the extinction of dinosaurs.
01:43Let's see now how they understood that.
01:46First of all, there were these 3D seismic images of very high resolution.
01:51They allowed researchers to separate the layers of the ocean floor
01:55and get a perfectly clear view of the crater.
01:58It's a bit like when you go from a blurry echography to 3D scans where all the details are visible.
02:03Their conclusions confirmed that the crater had been created by an asteroid
02:07with a width of between 457 and 5 cm.
02:10The impact was so intense that it produced a central peak,
02:14created ridges around the crater and even damaged a peripheral area of several thousand kilometers.
02:19With the help of these very detailed images,
02:22scientists have managed to reconstruct what happened
02:25just after the asteroid hit the surface of our planet.
02:28It first hit the ocean, creating a first crater in the shape of a tank.
02:33As the shock wave spread,
02:35the seabed was so violently shaken that there were several landslides.
02:40The furniture sediments surrounding the crater collapsed inwards,
02:44creating a well-visible edge.
02:47As you already know, the impact also triggered a tsunami
02:51whose power was such that the waves did not just spread outwards,
02:56but turned towards the crater,
02:58leaving huge scars on the ocean floor.
03:02And it wasn't just one big wave.
03:04No, there were a whole series.
03:07A succession of tsunamis destroying everything in their path.
03:11This second asteroid impact is a major event for scientists.
03:15It is a rare opportunity for them to study a marine impact crater in such detail.
03:21There are only about twenty confirmed marine craters in the world,
03:25and none of them have been observed with such precision.
03:28In addition, these data allow scientists to test new ideas
03:32on the formation of craters in aquatic environments.
03:35Unlike terrestrial craters,
03:37marine craters are hidden under layers of sediment,
03:41which makes them difficult to study.
03:43But thanks to this new 3D imaging,
03:46we can observe the crater on all its layers.
03:49It's like cutting a cake to see what it's made of.
03:53Dr. Nicholson and his team now dream of drilling into the crater
03:58to collect samples in the depths of the ocean floor.
04:03This would allow them to measure the shock pressure during the impact
04:06and understand what happened in the minutes,
04:09hours and days that followed the collision.
04:12Of course, the Chicxulub asteroid remains the star of the extinction of dinosaurs.
04:17This space traveler was gigantic.
04:20It measured between 10 and 14 km wide.
04:23It hit the Earth at a devastating angle,
04:26projecting rocks and gases vaporized in the atmosphere.
04:30It caused a winter of impact that lasted 15 years,
04:33because all these elements blocked the sun and plunged the Earth into darkness.
04:38The most intriguing thing is that some experts think that the asteroid Nadir
04:42could actually be a fragment of Chicxulub
04:45that would have detached before it hit the Earth.
04:49It's just a theory.
04:51But if it's true, it could mean that our planet
04:54was the victim of a double impact from space.
04:57Let's go back in time.
04:59Until 1908 and in Siberia.
05:01Look around you.
05:03You see nothing but trees and rivers.
05:06And suddenly, a huge object, 45 to 90 meters in diameter,
05:10crosses the Earth's atmosphere.
05:12Is it a comet? An asteroid?
05:15Scientists are not sure.
05:17What they are sure of is that this intruder exploded in the sky of Tunguska,
05:22causing one of the most powerful explosions in history.
05:26It completely razed the forest upside down,
05:29knocking down 80 million trees on a surface of about 2,150 square kilometers.
05:35It's a surface higher than that of cities like Los Angeles or New York.
05:40The trees were literally flattened,
05:43and their trunks stripped of their branches.
05:45Around the epicenter, it formed a strange radial pattern.
05:49And if this explosion had occurred above a city,
05:52all buildings would have been destroyed and countless lives would have been lost.
05:56Fortunately, this disaster occurred in a very remote region of Siberia,
06:01but the most frightening.
06:03When the scientists finally arrived in the region years later,
06:07they found no impact crater.
06:09So it is not surprising that the mystery remains intact.
06:13The most logical explanation is that when the object exploded in the sky,
06:17probably at a distance of 5 to 10 kilometers above the Earth,
06:21it disintegrated before touching the ground,
06:23which did not prevent the explosion from razing an entire forest.
06:27In 2013, another event blew up these products,
06:31this time above a much more populated area.
06:34The city of Chelyabinsk.
06:36It was on an ordinary morning in February that an asteroid of about 18 meters in diameter
06:41entered the Earth's atmosphere, illuminating the sky.
06:44It was moving at a speed of nearly 70,000 kilometers per hour.
06:49It exploded in mid-flight, about 29 kilometers above the city.
06:54The spectacle was terrifying,
06:56but fortunately the asteroid disintegrated high enough in the atmosphere
07:00and did not touch the ground.
07:02If it had, the city would have had very big problems.
07:05Indeed, even if there was no direct impact,
07:08the explosion still created a shock wave that crossed the atmosphere
07:12and hit the ground with enough force to break all the windows.
07:16The explosion damaged about 7,200 buildings,
07:19but luckily there were no direct victims.
07:22There is no doubt that this explosion was a real warning signal.
07:26It was not a distant cosmic event like the Tunguska.
07:30This asteroid exploded above a modern and populated area,
07:34and the damage is very real.
07:36The good news?
07:37Scientists are getting better and better at locating these objects
07:40before they get too close.
07:43Space agencies around the world, like NASA,
07:46track geocruisers to determine what could pose a risk.
07:52But as these two events show,
07:54it happens that space rocks surprise us.
07:58And if the chances of a major impact are low,
08:01the stakes remain very high.
08:03At present, NASA is monitoring an asteroid.
08:06This is Bennu, which is about the same size as the impactor Nadir.
08:10Bennu is considered one of the most dangerous objects in orbit near Earth.
08:14According to NASA,
08:15there is a low risk that it will hit Earth between 2178 and 2290,
08:22with a maximum danger on September 24, 2082.
08:27But don't panic right now.
08:29The probability of an impact is only 1 in 2700.
08:33This reminds us that the Earth is not safe from a cosmic disaster.