Saviez-vous qu'il se pourrait que ce ne soit pas un astéroïde qui ait exterminé les dinosaures ? Des recherches récentes suggèrent que l'activité volcanique et le changement climatique auraient pu jouer un rôle important dans leur extinction. L'impact de l'astéroïde a certainement causé le chaos, mais l'environnement changeant de la Terre mettait déjà à l'épreuve la population des dinosaures. Imaginez ces pauvres dinos faisant face à des éruptions volcaniques et à des changements climatiques drastiques en plus de l'impact de l'astéroïde ! C'est un revirement fascinant dans l'histoire de la disparition de ces créatures incroyables. Animation créée par Sympa.
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FunTranscript
00:00Are you sure that an asteroid is really responsible for the extinction of dinosaurs?
00:05The mystery surrounding the disappearance of these terrifying creatures
00:08arouses many debates, both in the scientific field and on the big screen.
00:12But what really happened?
00:14How did scientists elucidate this enigma?
00:17And why is it so important?
00:19Let's explore this question together.
00:21Let's go back to England in 1842,
00:24when a scientist named Sir Richard Owen
00:27devoted himself to the study of fossils of gigantic reptiles.
00:30He noticed that three of these creatures,
00:32the Megalosaurus, the Iguanodon and the Hilaeosaurus,
00:36had common characteristics.
00:38Seized by a brilliant intuition,
00:41he decided to group them under a new term,
00:44Dinosauria, meaning terrible, lizard in Greek.
00:50At that time, scientists were content to classify dinosaurs
00:54according to their appearance.
00:56Then, Charles Darwin came up with a revolutionary theory,
01:00species evolve over time.
01:03This idea shook up pre-existing conceptions
01:06and forced researchers to rethink the classification of dinosaurs.
01:10They introduced a new method called
01:13phylogenetic classification.
01:16Imagine a huge genealogical tree
01:19encompassing all the creatures that never existed.
01:22At the top of this tree,
01:24we find the Megalosaurus and the Iguanodon.
01:27And we say that all the descendants of these dinosaurs
01:30share a common ancestor.
01:32It's a bit like tracing your own genealogical tree
01:35to the original ancestor of dinosaurs.
01:38All this seemed to be an excellent plan
01:41until things got complicated.
01:44By studying dinosaurs,
01:46we discovered species with feathers,
01:49beaks and other blood.
01:51This is how we realized that birds were cousins of some dinosaurs,
01:56or even their direct descendants.
02:02After understanding this,
02:04scientists had to reexamine the genealogical tree of birds
02:08and redefine the very notion of dinosaurs.
02:11In the end, they concluded that birds were, in a way, dinosaurs.
02:16But not exactly.
02:18Disconcerting, isn't it?
02:20Anyway, we now have two distinct groups.
02:23The first is made up of birds.
02:25The second group is made up of non-avian dinosaurs,
02:28which are now extinct.
02:30Therefore, instead of asking ourselves
02:32what caused the extinction of dinosaurs,
02:35we should rather ask ourselves
02:37what caused the extinction of non-avian dinosaurs.
02:41The answer seems obvious.
02:43We often think that a gigantic asteroid
02:45is the cause of the extinction of dinosaurs,
02:48and this is probably the first idea that comes to mind.
02:51Even Google and other search engines agree on this point,
02:55like classmates copying their homework from each other.
03:02History teaches us that about 66 million years ago,
03:06dinosaurs practically all disappeared,
03:09except for those that evolved into birds.
03:12Of course, reality is more complex.
03:14All dinosaurs did not suddenly disappear.
03:17Some naturally disappeared,
03:19and minor extinctions occurred
03:21throughout their terrestrial existence.
03:23But the major event we are talking about
03:26looks like a change of scenery in a movie,
03:29as if a TV channel was suddenly turned on.
03:32And the Earth went from the era of dinosaurs to that of mammals.
03:36Scientists call these periods the Cretaceous and the Paleogene.
03:40We even have a name for this particular event,
03:43the K-Pg or K-T extinction.
03:46Some also refer to it as the event of 65 million years ago,
03:50although the most precise date is rather 66 million years.
03:54Two main theories predominate,
03:57the brutal impact of a repeated asteroid or volcanic eruptions.
04:01Let's talk about the hypothesis of the asteroid.
04:04Imagine, about 66 million years ago,
04:07a colossal asteroid hitting the Earth.
04:10This object was about 10 km in diameter,
04:13that is, a little bigger than Mount Everest.
04:16Breaking through the sky at a staggering speed,
04:19it moved at a hundred times the speed of sound.
04:22During its impact, it released an immense amount of energy.
04:26This cataclysm was called the K-Pg.
04:29This cataclysm occurred in what is now southern Mexico,
04:33near the famous crater of Chicxulub,
04:36linked to the extinction of dinosaurs.
04:39Everything that was near the impact was instantly vaporized.
04:43Imagine the most massive explosion that the Earth has experienced in several billion years.
04:47Nothing survived in this area.
04:50Then, the repercussions were felt.
04:53As the fireball dissipated, the surface of the Earth sank into chaos.
04:57The ground trembled and distorted,
05:00triggering earthquakes of unimaginable magnitude.
05:03The continents looked like huge inflatable castles in full delirium.
05:11Then, the debris projected into the atmosphere by the impact
05:14began to fall back into a dense rain.
05:17Even if you were not near the huge fragments falling in Mexico,
05:21you would have been hit by these tiny burning particles
05:25that were flying in the air.
05:27The atmosphere became so hot that entire forests
05:30spontaneously caught fire all over the world.
05:33And that's not all.
05:35Prepare for a gigantic tsunami.
05:37The bottom of the ocean was totally shaken,
05:40pushing gigantic waves into the land around the Gulf of Mexico.
05:45But even that was not enough to eradicate all the dinosaurs.
05:49Those of New Zealand, for example, seemed relatively spared.
05:53So what happened to make them all disappear?
05:56They first felt a slight shake,
05:59then the sky began to darken and become gloomy,
06:02as if it was night.
06:04And suddenly, a thick mantle of ash began to slowly envelop the entire planet.
06:13Now, this is where the real drama begins.
06:16The major problem with the impact of this asteroid
06:19does not lie in the explosion.
06:21As one might imagine, but rather in its long-term effects.
06:25Imagine the debris thrown into the sky,
06:27masking the light of the sun.
06:29The days turning into nights,
06:31and the temperatures falling abruptly.
06:33The herbivorous dinosaurs quickly periclited,
06:36leaving the carnivores feasting.
06:38But not for long.
06:40Without the light of the sun, the food chain collapsed very quickly.
06:44Then the ashes fell back on the ground,
06:47aggravating the situation again.
06:49Harmful elements, such as carbon dioxide,
06:52began to float in the air.
06:54This carbon dioxide, combined with fragments of the seabed,
06:57caused extreme temperature variations.
07:00The earth alternated between intense heat and ice cold.
07:04It was then that 50 to 80% of the dinosaur species disappeared forever.
07:09What is even more tragic,
07:11is that this figure only accounts for the species themselves.
07:14This figure is much higher,
07:16if we consider the number of affected individuals.
07:20We might think that the mammals
07:22finally had their chance after the disappearance of the dinosaurs.
07:25But even they had to go through difficult times.
07:28We are very lucky that some mammals,
07:30among the most resilient,
07:32survived this chaos.
07:34Those who survived were real little champions.
07:38Endowed with rapid metabolism,
07:40flexible food regimes,
07:42or perfectly sheltered terriers.
07:47But this story is just a hypothesis.
07:49There is another theory,
07:51that of volcanism.
07:53Volcanoes, these mountains of fire,
07:55are used to vomit lava,
07:57and to cause incomparable ravages.
08:00Surprisingly, this theory does not concern explosive eruptions,
08:04but something slower and more pernicious.
08:07About a million years before the disaster of the dinosaurs,
08:10a great upheaval occurred under the surface of the Earth.
08:14Deeply buried under what is now India,
08:17a river of magma began to form,
08:20gradually warming the region.
08:22Then, India was violently hit,
08:25turning into a sea of lava,
08:27similar to a burning ocean.
08:30As if a multitude of Ben trucks
08:32were slowly pouring out their lava content.
08:35These solidified residues are known as the Deccan Trap,
08:39a deep layer of solidified lava
08:41covering an area the size of France.
08:47Just like in our history of asteroids,
08:49the real problem with volcanism lies in the air.
08:53For hundreds of thousands of years,
08:55sulfur dioxide spread like an unstoppable shadow,
08:59darkening the sky and causing acid rains.
09:03Food sources turned into poison,
09:06and the oceans became acid baths.
09:08Then, carbon dioxide took over.
09:11It was like playing with a thermostat,
09:13completely disrupting the Earth's climate.
09:16This led to a real chaos.
09:19Ecosystems were disrupted,
09:22food chains were broken,
09:24and species were extinguished one after the other.
09:28These two theories seem quite credible.
09:31Experts engaged in great debates
09:33to determine which was correct
09:35and explain why dinosaurs disappeared.
09:38So, what is the real answer?
09:41Unfortunately, we still don't know.
09:43Some scientists defend a theory,
09:46while others prefer the latter,
09:48leaving us all perplexed.
09:51But don't be too harsh on the media or scientists.
09:55They do their best to elucidate the mystery
09:57of the disappearance of dinosaurs,
09:59and maybe one day we'll finally discover the real answer.
10:02So, stay tuned.
10:05NASA Jet Propulsion Laboratory, California Institute of Technology