The imperceptible rhythm of geological processes gives a sense of the immutability of the landscape, that appearance of stillness of the earth’s crust. The continents move at the same speed that our fingernails grow . In a century, what for the human being is a lifetime, little changes: the valleys, the mountains, the coasts were more or less the same as now. Twenty centuries of history allow us to see the change of course of a river, or a cliff that recedes a few meters, forming a beach where it did not exist before. As in those fast-motion movies where we see a flower open in a few seconds, we should take a frame of the Earth every 100,000 years to see the face of our planet change like we see a flower open . Only then could we see what is happening in the apparently calm desert of Djibouti: three plates are moving apart and have created the Great East African Rift, the Red Sea and the Gulf of Aden. Because of this, the last two have been filled with water. We could also see how the famous Andean Altiplano rose, 3,000 meters in 20 million years.
The most striking example of this exasperating geological slowness is found in Antarctica, right at the South Pole. It is not about the movement of a tectonic plate but that of the Antarctic ice, 3 kilometers thick. They move towards Africa and every year the scientists of the nearby McMurdo base must place a new pole that indicates the exact location of the South Pole , about 9 meters from the one placed the previous year.
Iceland, meanwhile, is an island of unfinished beauty. The violence of its volcanoes contrasts with the apparent stillness of its glaciers, its enormous waterfalls with the vast deserts of lava. Virtually treeless and exposed to the slow erosion of ocean, wind, water and ice, somewhere on the island a volcano erupts once every five years. Of all the lava that has appeared on the globe in the last 500 years, a third has done so in Iceland . Only 16 to 18 million years old, it is the youngest and most active island. But Iceland is also unique in another way. Although politically it belongs to Europe, geologically it is divided. Located just above the Atlantic ridge, half of the island belongs to the North American plate and the other half to the Eurasian plate. The tectonic tensions are separating the country into two halves at a rate of two centimeters per year. Some fissures that are easily visible in Thingvellir , the “Plains of Parliament”, a unique place where geology and history meet . There the Vikings established in 930 the Althing , the oldest living parliament, there the Icelanders converted to Christianity in the year 1000 and there they declared independence from Denmark in 1944. To those plains cracked by dozens of fissures that clearly show how the crust stretches and tears, Viking farmer-warriors from all over the island used to flock to their annual Althing rendezvous.
The Himalayas and the climate
The Himalayan mountain range is living proof of the dramatic consequences of plate tectonics. When two continents collide neither of them subducts (sinks under the other) as happens when two oceanic plates meet or one continental and one oceanic. The rocks that compose it, being relatively light, resist sinking and behave like two icebergs colliding in the sea .
In this case, 50 million years ago the Indian and Eurasian plates collided. The consequence was not only the appearance of Everest, but a region the size of France located north of the Himalayas was thrown upwards an average of about five kilometers above sea level: the Tibetan Plateau .
The unstoppable and terrifying rise of the highest mountain range in the world has occurred in the last 10 million years and even today it continues to rise at a rate of two millimeters per year . If a distant descendant of Edmund Hillary wanted to plant his flag on top of Everest at the end of the 21st century, he would have climbed almost three meters higher than his ancestor. Now, why does it continue to rise? Explaining it is a major challenge for plate tectonics.
Interestingly, the Himalayas are also important for meteorology. The monsoon season in South Asia is preceded in the summer by low atmospheric pressure across the Tibetan Plateau . And not only that. According to oceanographer Maureen Raymo and paleoclimatologist Bill Ruddman, the appearance of the Himalayas reshaped the Earth’s climate by reducing, by different mechanisms, the amount of carbon dioxide present in the atmosphere . Just the opposite of the famous greenhouse effect, its virtual disappearance caused a continuous drop in temperatures 55 million years ago that culminated in a cycle of ice ages that in the last two million years has changed the appearance of the planet.
Thanks to this hypothesis, it is explained why this mountain range underwent a rapid ascent two million years ago –just at the time of the first ice age–: a colder environment favors a greater erosive effect by the glaciers in the valleys, that take a large amount of material and, as if it were a cork, the surrounding peaks ascend. Although this hypothesis has not yet been proven, it is curious to see that both the Pyrenees, the Rockies and the Alps seem to have increased in height in the last three million years.
200 million years ago, the Pangea supercontinent broke into two: Gondwana in the south and Laurasia in the north. Within 250 million years something similar will happen, forming another supercontinent, Pangea Ultima . But before that, in 50 million years, the Mediterranean – the remnant of a much larger ocean that has been closing for the last 100 million years – will have closed completely. The clash of Africa with Europe will cause the appearance of a new Himalaya, perhaps in Spain or in another point of southern Europe. For its part , Australia will rotate and collide with Borneo and southern China as the Indian subcontinent did 50 million years ago. The Atlantic will have opened up even more, but not forever. According to Christopher Scotese, from the University of Texas, a new subduction zone may appear that will reverse its movement and the Atlantic will end up closing. It will be 250 million years from now – if the predictions are correct – when all the current continents will merge into one, as if it were a remake of an old movie .
Fortey, R. (2004) Earth: an intimate history, Vintage Books
Lunine, J. I. (1999) Earth: evolution of a Habitable World, Cambridge University Press
Nield, T. (2007) Supercontinent, Harvard University Press