La croûte terrestre fait quelque chose d'assez intense—elle se casse lentement ! Les scientifiques disent que les plaques tectoniques, ces immenses pièces de puzzle qui composent la surface de notre planète, se déplacent et se fissurent plus que jamais. Cela pourrait signifier un grand changement dans la façon dont les continents et les océans sont formés sur des millions d'années. C'est comme si la Terre se préparait pour un tout nouveau chapitre. Ne vous inquiétez pas, cependant—ce n'est pas quelque chose qui arrive du jour au lendemain, pas de gouffres soudains ou de nouveaux océans demain. Cependant, c'est fascinant de penser que le sol sous nos pieds est toujours en mouvement, façonnant petit à petit l'avenir de la planète. Animation créée par Sympa.
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FunTranscript
00:00Presented for more than 3 billion years,
00:02a part of the oldest terrestrial crust disintegrates today.
00:06While the continents seem to be immobile,
00:09they have undergone significant displacement and rearrangement over time.
00:13This phenomenon is made possible by tectonic activity,
00:16which causes the slow sliding of terrestrial plates,
00:19like the pieces of a vast jigsaw puzzle in motion.
00:22The most stable parts of these jigsaw pieces are designated by the name of cratons.
00:26These rock formations, both very ancient and extremely resistant,
00:31constitute the roots of the continents and ensure their cohesion.
00:35The North American craton, for example,
00:37encompasses a large part of the United States,
00:39about half of Canada,
00:40as well as the majority of Greenland.
00:43Scientists have identified nearly 35 major cratons around the world.
00:48Thanks to their robustness,
00:49these structures have remained practically immutable for hundreds of millions of years.
00:54However, in 2014,
00:56it was discovered that their allegedly indestructible character was not absolute.
01:01Some cratons have lost part of their solid roots
01:05as a result of specific geological processes,
01:08resulting in a weakening and fragilization of their structures.
01:12These observations suggest that additional tectonic modifications
01:16could compromise their stability.
01:18In 2024,
01:20scientists from the University of Geosciences of China
01:22have analyzed an ancient terrestrial mass called the North China Craton,
01:26or NCC in abbreviated.
01:29They wanted to know more about how some of the oldest rock regions on Earth
01:33could dislocate.
01:35This process of disintegration of the cratons is called decratonization.
01:40The NCC arouses particular interest
01:42because it consists of three main subdivisions,
01:45the Western Block,
01:46the Eastern Block,
01:48and the Trans-North China Orogene,
01:50an intermediate zone located between these two blocks.
01:53Studies have shown that during the Mesozoic Era,
01:56the Eastern Block lost its ancient roots
01:59as a result of intense tectonic and magmatic movements,
02:02known as tectonomagmatic events.
02:05Scientists have sought to understand precisely
02:08how the processes within the terrestrial mantle
02:11and the movements of the tectonic plates
02:13led to the disintegration of the NCC.
02:16They have developed four-dimensional models
02:18to illustrate the evolution of its shape over time,
02:21including the changes in its surface,
02:23the stretching of its layers,
02:25as well as the propagation of seismic waves within it.
02:28They found that part of the tectonic plate
02:30had sunk under the craton before receding.
02:33This return movement accompanied by a stretch
02:36led to a softening of the solid rock,
02:38making it unstable.
02:40This process would have begun about 200 million years ago,
02:43during the Jurassic Period,
02:45at the time when dinosaurs reigned on the planet.
02:48The North China Craton is not the only region
02:51affected by the phenomenon of decratonization.
02:54Other cratons, such as those in North America,
02:56South America,
02:57or even the Yangtze region in China,
03:00could have experienced similar evolutions.
03:03Researchers believe that this illustrates
03:05the progressive transformations of terrestrial continents
03:08over billions of years.
03:09In geology,
03:10no place seems completely safe from such upheavals,
03:14but this is not a reason to worry.
03:17You may not notice it,
03:18but our planet is constantly moving.
03:21A perfectly natural phenomenon.
03:23However,
03:24these movements can sometimes lead to spectacular transformations.
03:29In 2017,
03:30scientists officially announced that Zealandia
03:33could be considered a new continent.
03:36The continental plateaus of this mysterious territory
03:39lie at a depth of about 1,000 meters
03:42below sea level.
03:43The oceanic crust plunges even deeper,
03:46reaching 3,000 meters.
03:48Geologists have explored these depths
03:51to retrieve samples from the ocean floor.
03:54They discovered
03:56that unlike the neighboring oceanic crust
03:58composed of recent basaltic rocks,
04:01the crust surrounding New Zealand
04:03is made up of a mixture of ancient granite,
04:05limestone, and grey,
04:07characteristic of a continental crust.
04:10In addition,
04:11researchers have discovered a narrow strip of oceanic crust
04:14that separates Australia from the concealed territory of Zealandia.
04:17This proves that these two regions are distinct continents.
04:2185 million years ago,
04:23Zealandia separated from the supercontinent Gondwana.
04:26Millions of years later,
04:27the powerful Pacific plate,
04:29a true champion of tectonic plates,
04:31plunged under the continental crust of Zealandia.
04:34This is how the root of Zealandia,
04:36this connection to its continental crust,
04:38broke,
04:39and sank into the sea depths.
04:42And this is not the only new tectonic plate
04:44from this region of the world.
04:46120 million years ago,
04:47Australia and Antarctica
04:49were one and the same piece of land.
04:52After having borrowed different trajectories,
04:54Antarctica did not leave without taking anything.
04:57Today,
04:58in the Indian Ocean,
04:59there is an oceanic plateau that,
05:01in the past,
05:02was linked to another lost continent,
05:04the microcontinent of Kerguelen.
05:07Scientists estimate that it served as a terrestrial bridge
05:10between India and Antarctica.
05:12To better understand,
05:13just observe the Kerguelen archipelago,
05:15located in the South Indian Ocean.
05:18These islands are the last remains of this ancient continent.
05:21They have a cold climate
05:22and are covered with glaciers
05:24due to their proximity to Antarctica.
05:27However,
05:27in the past,
05:28the climate there was more temperate,
05:30with abundant rainfall.
05:33The fauna and flora there were undoubtedly similar
05:36to those currently found in tropical regions.
05:39Another lost continent,
05:40as for it,
05:41does not hide under the waves,
05:42but under Europe itself.
05:44It bears the name of Great Adria
05:46and collided with the European continent
05:49before starting to sink under it,
05:51about 100 million years ago.
05:53Currently,
05:54it is located under Italy,
05:56Greece and the Balkans.
05:58Its size,
05:58and even its shape,
05:59recalls that of Greenland,
06:01the largest island in the world.
06:03Great Adria is no longer visible today,
06:05but it has left many traces.
06:07Some of its parts have been integrated into the Alps,
06:10other fragments are found in Italy and present-day Croatia,
06:13on the other side of the Adriatic Sea.
06:16The limestone rocks from this ancient continent
06:18began to transform once buried
06:21under the European terrestrial mass.
06:23The intense heat
06:24and the pressure exerted for tens of millions of years
06:27have altered their structure.
06:29This is how limestone disappeared to the benefit of marble.
06:32Great Adria
06:33was not a solid land
06:34like the continent we know today,
06:37but rather
06:38an immense shallow underwater platform.
06:41Over time,
06:41sand, mud and various materials
06:44have accumulated on this platform
06:46to gradually turn into rock.
06:48Great Adria could have looked like Zealandia
06:51or the Keys of Florida,
06:53an island chain located in a shallow sea.
06:56Above the water,
06:57there were probably many islets and archipelagos,
07:00while under the waves,
07:01multicolored coral reefs
07:03were full of life.
07:05If you had lived there at that time
07:06and had diving equipment,
07:08this place would have offered an ideal setting
07:11for underwater exploration.
07:12With all the upheavals related to the craton,
07:15who knows,
07:16we could witness the emergence
07:18of a new continent in the future.
07:20The in-depth study of the terrestrial crust
07:22could shake our understanding
07:23of the history of the planet.
07:25In Copenhagen,
07:26scientists made a fascinating discovery
07:29about the real origin of Scandinavia.
07:31And it is not where we thought it was.
07:34After analyzing the sand and rocks
07:36from isolated regions of Finland,
07:39they concluded that the roots of Scandinavia
07:42actually came from Greenland,
07:44more than 3.75 billion years ago.
07:48This means that the current region
07:50of the Nordic countries,
07:51Denmark, Sweden, Norway and Finland,
07:54is actually 250 million years older
07:57than what scientists had previously imagined.
08:00This discovery was made possible
08:02thanks to tiny crystals called zircons,
08:05discovered in the sands of the Finnish rivers.
08:08By studying their chemical composition,
08:10researchers found that the age of the crystals
08:12corresponded to that of the rocks of Greenland
08:14and not Scandinavia.
08:16Scientists used specific techniques
08:19to analyze elements such as uranium,
08:21lead,
08:22lutetium
08:23and afnium,
08:24and thus determined that the rocky base
08:26of Scandinavia
08:28was probably detached from Greenland
08:30several billion years ago.
08:32A small grain of earth
08:34would then have drifted through the earth's surface
08:37for hundreds of millions of years.
08:39This fragment would have finally settled
08:41where Finland is today.
08:44Over time,
08:45new rocky layers formed around this grain,
08:48giving birth to the Scandinavia
08:50that we know on current maps.
08:52This same study could encourage us
08:54to review the way in which the continents of the Earth
08:57were initially formed.
08:59The most widespread theory suggests
09:01that continental crust
09:03began to develop
09:04as soon as the planet was formed,
09:06about 4.6 billion years ago.
09:09However,
09:10recent research shows
09:11that the growth of continents
09:12began only a billion years later.
09:14According to scientists,
09:16terrestrial continents
09:17may have emerged
09:19from small grains
09:21of ancient crust
09:22distributed in various parts of the planet.
09:25These grains developed over time,
09:27forming the current terrestrial masses.
09:29They are not only found in Scandinavia,
09:32but also in Australia,
09:33South Africa and India.
09:35However,
09:36researchers do not know
09:37if all these grains come from the same place,
09:40or if they developed independently
09:42in different regions.
09:43There is therefore a lot to discover,
09:45and it is essential
09:46that scientists
09:48continue their research
09:49to determine
09:50whether all these ancient grains
09:51are connected.