If you can overlook the insignificant lifeforms on its surface, its own history of Earth is the slow expansion of its continents. Billions of years ago our planet was largely a liquid world-wide with a few small islands poking above the surface. Then, as now, the flooring of the atlantic provinces bore more resemblance to the composition of the other rocky planets than it does to continental rocks. The question of how continents came to cover so much of countries around the world has perplexed geologists, but a new belief commits the credit to mountain ranges.
The idea is counter-intuitive. After all, if there were no continents, where would the mountains sit? Nevertheless, Dr Ming Tang of Rice University said in a statement: “If our conclusions are chastise, every piece of land that we are now sitting on got its start someplace like the Andes or Tibet, with extremely mountainous surfaces.”
Many of the world’s mountain ranges are eroded continental arcs, located at the margin where a continental layer rode over an oceanic one. Tang proposes these arcs are factories for the distinctive continental rocks.
Tang’s hypothesis, presented in Nature Communications, is based on the distribution of niobium and tantalum in stones all over the world. Although the two metals’ calls sound like they are from science fiction and fantasy works respectively, the elements are so chemically similar they usually turn up in the same places, leaving a extremely constant ratio.
However, the continental layer has 20 percent less niobium, proportionally, than the rest of the planet. The missing niobium has troubled geologists for decades.
Tang studied databases of the elemental composition in stones, and came to the conclusion the continental average is being dragged down by arclogites, information that collect at the basi of continental arcs. Although often deep buried, arclogites can be brought to the surface by volcanoes.
Tang had arclogites from the High Sierras tested and supported those made use of rutile crystals are high in niobium. He envisages these crystals captured a lot of niobium, but not tantalum, and most of them descend into the mantle, leaving low-toned niobium crust behind.
Rutile exclusively structures under high pressures, such as is provided at the base of the crust with a mountain range above. While the niobium content afforded the evidence that allowed Tang to recognize what was happening, the more important aspect of the minerals formed by the continental arc is that their low iron content becomes them lighter, and therefore more buoyant than oceanic basalts.
Where the first continental arc came from is ambiguou, but once it showed, it began a self-reproducing cycles/second. The arc rendered continental stone, which rode over any oceanic platefuls it encountered, making more continental arc, and therefore more continents.