Les chercheurs ont trouvé des preuves convaincantes que le mercure ancien, enfoui dans les roches, indique que de massives activités volcaniques sont la cause de la plus grande extinction de masse sur Terre, connue sous le nom de « la Grande Mort ». Cet événement catastrophique s'est produit il y a 252 millions d'années et a éliminé plus de 95 % de la vie sur Terre, redéfinissant radicalement la biodiversité de la planète. Le mercure, libéré par d'importantes éruptions volcaniques, s'est déposé dans les roches et fournit une signature géochimique qui relie ces éruptions à l'événement d'extinction. Selon l'étude, ces éruptions volcaniques ont conduit à de graves changements climatiques, à l'acidification des océans et à la destruction généralisée des habitats. Animation créée par Sympa.
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FunTranscript
00:00Our planet has experienced five massive extinctions.
00:03One of them was so devastating
00:05that it destroyed more than 95% of life forms on Earth,
00:09and scientists think they have found the culprit, the volcanoes.
00:14By analyzing ancient rocks from a dozen sites around the world,
00:18they have discovered high levels of mercury,
00:21released by volcanoes millions of years ago.
00:24This suggests that volcanic eruptions
00:26are probably the cause of the extinction of Permian Trias.
00:30Mercury was not only found in rocks, but also in the atmosphere.
00:34This means that when volcanoes erupted,
00:37they released this toxic gas into the air.
00:40They spat out about 3 million cubic kilometers of ash,
00:43much more than the famous eruption of Mount St. Helens.
00:47The gas left a mark on one of the most significant disasters in history,
00:51and prepared the ground for the era of dinosaurs.
00:54These eruptions also probably released mercury
00:57by inflating large deposits of coal.
01:00The shallower waters revealed mercury spikes
01:03just at the main horizon of the extinction.
01:06While the deeper sections recorded spikes
01:09several tens of thousands of years earlier.
01:12This could mean that the effects of volcanic activity
01:15and the extinction it caused
01:17varied according to the different oceanic depths.
01:20It also means that this extinction was prolonged and complex.
01:24It not only resulted from a major global warming at the time,
01:27but also caused other harmful effects,
01:29such as acid rains,
01:31aggravating the situation for plants and animals.
01:34Although few traces of Permian have survived to this day,
01:37we can get an idea of what the world looked like at that time
01:41thanks to the fossils discovered in eastern Kansas.
01:44252 million years ago,
01:46the earth was in full abundance.
01:48The terrestrial continents gathered to form the supercontinent Pangaea.
01:52The earth was mainly arid,
01:54resembling an austere desert
01:56with vast rocky expanses
01:58and few water sources.
02:00The climate alternated between hot summers
02:02and icy winters.
02:04Some plants, mainly conifers,
02:06giant ferns and primitive mosses
02:09grew in areas with a little water.
02:12The earth was dominated by creatures similar to dinosaurs,
02:15such as pelicosaurs and therapsids,
02:18often called mammalian reptiles.
02:20The formidable Dimetrodon,
02:22with its remarkable veiled dorsal fin,
02:25was also one of the main predators of the time.
02:29Small reptiles and amphibians also populated the landscape,
02:32alongside emerging insects such as beetles and dragonflies,
02:35which thrived in this dry environment.
02:38But the most interesting events
02:40took place mainly in shallow tropical seas.
02:44The marine environments were full of life,
02:47rich in coral reefs,
02:49a quantity of molluscs called brachiopods,
02:52bryozoares and large unicellular fusilinidae,
02:56resembling small forms covered in moss.
02:59Ammonites, small and fascinating,
03:02were also widespread,
03:04evolving alongside brachiopods,
03:06bonefish and sharks.
03:08Trilobites,
03:10ancient marine organisms
03:12that lived for the first time 500 million years ago
03:14during the Cambrian period,
03:16persisted until the Permian period.
03:18They were highly diversified,
03:20ranging from active predators to carnivores,
03:22as well as plankton eaters.
03:24However, almost all these magnificent creatures
03:27would be brought to extinction
03:29during the extinction of the Permian-Trias.
03:31It proved to be truly pitiful.
03:34More than two-thirds of amphibian and reptile species
03:36disappeared,
03:38and nearly one-third of all insect species
03:40were destroyed.
03:42Usually, insects are among the most resilient
03:44among the survivors,
03:46which illustrates the extent of this event.
03:48Among these missing animals
03:50was the terrifying Meganeuropsis,
03:52a giant libellule
03:54with a width of nearly 80 cm,
03:56which lived in the center of Kansas
03:58near Elmo.
04:00The place is famous for its rich collection
04:02of insect fossils of the Permian,
04:04including crickets and ancient slugs.
04:06For some time,
04:08the exact cause of this event
04:10has remained mysterious.
04:12Theories allude to the impact
04:14of a huge asteroid
04:16on natural pollutants
04:18depriving the oceans of oxygen,
04:20as well as dust clouds
04:22resulting from colossal volcanic eruptions
04:24that would have masked the sun
04:26and cooled the planet.
04:28There is evidence supporting each of these scenarios.
04:30However, a recent discovery
04:32seems to favor volcanoes.
04:34It is also possible
04:36that the cause of this extinction
04:38is not limited to volcanoes.
04:40Researchers funded by NASA
04:42have recently discovered what could be
04:44the digital footprints of this former
04:46responsible, or at least one of his accomplices.
04:48Studying rocks from all over the world,
04:50they found clues suggesting
04:52that a massive impact of asteroids
04:54could also be involved.
04:56They discovered unusual molecules
04:58in the form of rugby balls
05:00and called fullerenes.
05:02These molecules contain rare gases
05:04of extraterrestrial origin
05:06suggesting that a huge asteroid,
05:08perhaps as large as Mount Everest,
05:10would have crashed on Earth,
05:12contributing to the extinction.
05:14It seems that a series of catastrophic events
05:16have occurred.
05:18Volcanoes have spat out
05:20huge amounts of lava and gas,
05:22thus altering the climate.
05:24The formation of the Pangea
05:26disturbed the meteorological and oceanic
05:28patterns, and an asteroid
05:30also hit the Earth.
05:32We still find a way to be reborn,
05:34proving the adaptability of our planet.
05:38It is interesting to note that
05:40this was not an isolated event.
05:42The extinction of the late Devonian
05:44about 360 million years ago
05:46is also linked to volcanic activity.
05:48The eruptions and proliferation
05:50of terrestrial plants
05:52could have changed the flow of nutrients
05:54towards the oceans.
05:56The extinction of the Jurassic Trias
05:58occurred about 200 million years ago,
06:00shortly before the appearance of dinosaurs,
06:02could also be due to the combination
06:04of volcanic eruptions
06:06and an impact of asteroids.
06:08Finally, about 66 million years ago,
06:10a last drastic change
06:12took place on Earth.
06:14Our planet went from the era
06:16of dinosaurs to that of mammals.
06:18This size change
06:20is known as the Cretaceous-Paleogene
06:22extinction.
06:24Like the Permian extinction,
06:26it is a sudden event that
06:28produces new forms of life.
06:30And, once again, two great theories
06:32explain what happened.
06:34The most widespread theory
06:36states that dinosaurs would have
06:38disappeared because of a huge asteroid.
06:40The Chicxulub meteorite
06:42crashed into what is now
06:44the south of Mexico,
06:46forming the crater that bears its name.
06:48This meteorite was about 10 km in diameter
06:50and headed towards Earth
06:52at a prodigious speed.
06:54The impact instantly vaporized
06:56everything that was nearby
06:58and released an unequal amount of energy
07:00in a billion years.
07:02The consequences were catastrophic.
07:04Earthquakes shook the continents
07:06and the ground wavered like a
07:08flooded sea. The dust raised
07:10by the asteroid fell back on Earth
07:12in a scorching rain, heating
07:14the atmosphere to the point of burning
07:16the forests of the entire world.
07:18Shortly after, a gigantic tsunami
07:20caused by the upheaval of the seabed
07:22submerged the coasts
07:24near the Gulf of Mexico.
07:26All the dinosaurs did not
07:28instantly disappear. In regions
07:30like New Zealand, some populations
07:32first survived. However,
07:34a sky obscured by ashes
07:36ended up enveloping the planet,
07:38hiding the sun and plunging the world
07:40into cold and darkness.
07:42This long-term effect
07:44truly sealed the fate of the dinosaurs.
07:46Without sunlight, the food chain
07:48quickly collapsed.
07:50Herbivores slowly disappeared,
07:52followed by carnivores that depended on them,
07:54while ash falls
07:56accentuated environmental
07:58upheavals and temperature fluctuations,
08:00making survival difficult.
08:02However,
08:04there is another theory according to which
08:06the asteroid would have been
08:08only a stroke of grace. The extinction
08:10of the dinosaurs was already
08:12inevitable because of the volcanoes.
08:14About a million years before their
08:16disappearance, an intense volcanic activity
08:18began in the subsoil of
08:20the present day. This event created
08:22the famous Deccan Trap,
08:24a vast lava plateau covering
08:26a surface as large as France.
08:28For hundreds of thousands
08:30of years, these volcanoes ejected
08:32sulfur dioxide and carbon dioxide
08:34into the atmosphere, darkening the
08:36skies and causing acid rain,
08:38poisoning food sources
08:40and turning the oceans into toxic baths.
08:42These gradual but relentless changes
08:44put the ecosystems to the test,
08:46breaking down food chains
08:48and causing a slow but continuous decline
08:50of many species, including dinosaurs.
08:52Although we do not know
08:54with certainty which theory is
08:56the most precise, scientists now
08:58think that the two phenomena
09:00played a role. Maybe one day
09:02we will have a clear picture of how
09:04the reign of dinosaurs
09:06ended so abruptly.