00:00The distance between New York and Lisbon, across the Atlantic, is well over 5,000 km.
00:06At an average walking speed, such a journey could be accomplished in about a month and a half,
00:11not counting the stops to rest and the necessary sleep.
00:14Although buying a plane ticket or embarking on a ship is one of the more judicious options,
00:19these are, to this day, the only ways to cover this distance.
00:23But if such a crossing on foot became conceivable one day, would you be tempted to take up this challenge?
00:28The most obvious obstacle remains the vast expanse of water that is the Atlantic Ocean,
00:33which covers about a fifth of the Earth's surface.
00:36The oceans as a whole occupy nearly 70% of the planet.
00:41When you open the tap or buy a bottle of water, you only consume a tiny part of this drinkable resource.
00:47Indeed, 97% of the Earth's water is contained in the oceans, in the form of saltwater, unsuitable for consumption.
00:55If we add the 2% of water trapped in the calottes and glaciers, less than 1% of the Earth's water is actually drinkable.
01:05If you were to convert these percentages into figures, you would need a very long sheet of paper.
01:10According to the US Geological Survey estimates, the volume of water on Earth exceeds 138,600,000 cubic kilometers.
01:18This resource is essential for the maintenance of all forms of life, including human.
01:22The oceans also play a key role in the regulation of global air temperatures.
01:27Without them, the regions located around the equator would experience extreme heat.
01:32This imaginary line, separating our planet into two hemispheres, passes through 13 countries, such as Brazil, Kenya and Indonesia.
01:40The oceans of the globe are fundamental to the water cycle on Earth, a process that you have probably studied at school.
01:47The precipitation from the clouds ends up feeding the rivers, which are then thrown into the oceans.
01:53As a result of solar radiation, this vast mass of water evaporates, rises into the atmosphere and forms new clouds, thus perpetuating the cycle.
02:02This mechanism directly influences the global climate.
02:06This is why the Mediterranean is so popular during the summer holidays, because the region benefits from a pleasant and temperate climate.
02:15If we remove the oceans from the equation, the water cycle would stop.
02:20The vast area they occupied would transform into a gigantic surface of dust.
02:25The dried up soil would spread out at a loss of sight.
02:28Without evaporation, the clouds would no longer form, making the precipitation rare.
02:33Humanity would quickly be deprived of drinking water sources.
02:36The landscape of our planet would turn into a huge desert, similar to a Sahara spreading over its entire surface.
02:43The aridity would be such that fires would easily ignite, driven by the dry atmosphere.
02:49This would certainly not be ideal conditions to undertake a long walk between continents.
02:54But let's assume that you have survived this new environment.
02:57You then embark on a walk through this desert land, which used to be the Atlantic Ocean.
03:03What would this journey look like?
03:05You would be confronted with a landscape radically different from the one visible above the marine surface.
03:11What lies beneath the waves exceeds in height and depth the world we know.
03:16It is a kingdom of extremes.
03:18Take, for example, the highest mountain on our planet.
03:21If the Himalayas and its summit, Mount Everest, come to mind, you are partly right.
03:29This chain is the highest when measured from the level of the sea, reaching just over 8,848 meters.
03:36However, if we consider the height of a mountain from its base to its summit, the Himalayas loses its first place.
03:43In reality, the highest summit on Earth is Mount Mauna Kea, located in Hawaii.
03:48This dormant volcano, whose name means White Mountain in the local language, is partially submerged under the Pacific Ocean.
03:56Its total height exceeds Mount Everest by nearly 1.6 kilometers, culminating at 10,211 meters.
04:04Currently, it is difficult to appreciate its magnitude.
04:07But if the Pacific dried up, we could admire the base of this giant in full light.
04:12The bottom of the Atlantic Ocean also houses a comparable mountain range, which constitutes the largest geological structure on our planet.
04:20This formation, the Medio-Atlantic Dorsal, is almost entirely submerged under the waters.
04:25It rises from the ocean floor to an altitude that reaches about half that of Mount Kilimanjaro, in Tanzania.
04:34The width of this massive submarine chain is one tenth of the Earth's diameter.
04:39The only visible portions of the Medio-Atlantic Dorsal manifest themselves in the form of islands, such as Iceland and the Azores.
04:47The island inhabited by the most remote in the world, Tristan da Cunha, is also part of the rare elements of this geological formation that emerges from the sea.
04:55What is perhaps even more impressive than its size is the date of the discovery of this dorsal.
05:01It was only in the 1950s that scientists established cartography.
05:05Considering that our civilization dates back several millennia, this seems recent.
05:10And reveals how much our knowledge of ocean depths remains limited.
05:14According to UNESCO, humanity has explored only barely 5% of the Earth's oceans.
05:19As surprising as it may seem, more people have set foot on the Moon than on the seabed.
05:25And the deepest point of our planet is located in the Marianas Gorge of the Pacific Ocean.
05:32The discovery of the Medio-Atlantic Dorsal has raised the veil on the mystery of the formation of continents and oceans.
05:38By understanding the origins of these structures, you can better anticipate what awaits you during an imaginary crossing of the Atlantic.
05:45The Dorsal is located directly between North America and Europe.
05:49But it is convenient not to consider these terrestrial masses only as continents, but rather as tectonic plates.
05:56These represent huge segments of the lithosphere, the external layer of the Earth, mainly made up of rocks.
06:04Our planet has between 15 and 20 of these massive plates, which rest on a partially melted rock layer.
06:10Although they do not float, scientists use this term to best describe their instability.
06:19The tectonic plates are in perpetual motion and can collide.
06:24In these cases, one of the plates plunges, while the other is pushed up, releasing immense amounts of energy.
06:31On the surface, this is manifested by earthquakes and eruptions.
06:35These tectonic forces shaped our planet as we know it, and this is how the Himalayan mountains were formed about 40 to 50 million years ago.
06:45During this period, the Indian plate moved north, hitting the southern edge of the Eurasian plate.
06:52Since these two plates are made up of similar rocks, none of them plunged under the other.
06:57The only option was a push up.
06:59This process is still underway, and each year the Himalayan chain continues to rise by a centimeter.
07:07A comparable phenomenon occurs at the level of the Medio-Atlantic Dorsal, which widens by about 4 cm each year.
07:14This process has an intriguing side effect.
07:17If you remember the time when you built sand castles, you had to dig all around to raise the dungeon.
07:23Thus, the hole grew as the castle grew in size.
07:28In the Atlantic, a similar process is underway, but on a colossal scale.
07:33As the Medio-Atlantic Dorsal expands, the opposite coasts, carried by the North American and Eurasian plates, move away from each other.
07:41This could extend your hypothetical crossing of a world without oceans.
07:45Each year, this imaginary journey would extend by 2 to 3 cm.
07:50Although it seems insignificant today, in the distant future, you could even see the continents drift to you, making your journey useless.
08:01Evaporation is not the only mechanism that can cause an ocean to dry up.
08:06The opposite coasts could simply close on it.
08:10And scientists believe that this scenario will occur in the Pacific.
08:14In nearly 50 million years, the largest ocean on Earth will be unrecognizable.
08:19By performing computer simulations, experts have studied the future trajectory of the North and South American plates, which are heading towards the North Pole.
08:28In the long run, they will merge with Asia to form a new supercontinent.
08:33Which will profoundly change the appearance and size of the Pacific Ocean.
08:37This new set of emerged lands already bears a name.
08:41Amazigh.
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