‘The Earth’s Shell Has Cracked, and We’re Drifting on the Pieces’ read the startling headline in a recent issue of The New York Times.
The earthquakes and aftershocks that have shaken Nepal since April 2015 remind us that the entire Himalaya range, all 2,000 kilometers of it from Pakistan to Bhutan, is at the edge of one of those great cracks in the Earth’s shell and that South Asia is adrift and slowly colliding with Central Asia. You don’t have to be a geologist to understand that the awkwardly upended strata and startlingly abrupt mountains rising high in places like upper Mustang reflect some powerful lurches and lithers of Mother Earth over a great many millennia. And there are undoubtedly more to come.
The NYTimes story is all about ‘Plate Tectonics’ and ‘Continental Drift’ and their combined effect on our lives and landscapes.
It has been only a few decades since geologists determined that Earth’s crust is broken into segments, eight or nine are large, and another five or six are small. The two associated with Nepal are Gondwana (the landmass of South Asia) and Laurasia (Tibet and beyond at the north).
The Gondwana mass broke up toward the end of the Paleozoic Era (570 to 230 million years ago) into what we now call South America, Africa, Antarctica, Australia, and the Indian subcontinent. Between Gondwanaland and Laurasia was an ancient sea called Tethys, whose muddy bottom fostered ancient life which became the ammonite fossils called ‘saligrams’ found at some very high elevations in the ‘Tethys Himalayas’, the northernmost and highest parts of region. The greatest evidence of the Tethys Sea in Nepal is in the upper Kali Gandaki river valley of Mustang District and in India in Himalchal Pradesh’s Spiti Valley.
Inits relentless northward crawl, Gondwana eventually pushed the Tethys Sea aside and, by a slow geological process known as subduction, it began to slide dramatically, but in human terms almost imperceptively, under Laurasia. This resulted in the dramatic Himalayan upthrust, marked by countless violent earthquakes over eons of time. The tectonic plates are still moving, at an estimated five centimeters per year, though earthquakes tend to speed it up.
Think of “Earth’s outer shell,” the NYTimes writer tells us, “broken up into giant puzzle pieces, or plates, all gliding atop a kind of conveyor belt of hot, weak rock: here rising up from the underlying mangle, there plunging back into it.” This explains some of the amazing behavior and conditions of Planet Earth: how it got its high mountains and deep ocean canyons, why it suffers from catastrophic earthquakes, volcanic eruptionsand tsunamis, the composition of the very air we breathe, and the foundation of our entire biosphere. The biosphere is the sum of life and all ecosystems existing on or near the very thin surface of our planet.
And why is this important? Scientists argue about it, but since “Science is a democratic process,” as one has put it, most geologists now agree that plate tectonic behaviors first began around 2.5 to 3 billion years ago.
Knowing “when and how Earth’s vivid geological machinations arose will do more than flesh out our understanding of our home base,” the NYTimes writer tells us.But one geoscientist goes further by forewarning that if and when we earthlings go off searching for a new planet to colonize, we should avoid ones with plate tectonic activity. That’s where life is likely to have evolved beyond the “single cell or worm stage,” he says,“and we don’t want to fight another technological civilization for their planet.”
The New York Times article, by Natalie Angier, was published on December 18, 2018. You can read it online at www.nytimes.com/2018/12/18/science/plate-tectonics-continents-earth.html, and for more, search “plate tectonics” at www.ScienceDaily.com. In Greek mythology, Tethys is the goddess of the sea, daughter of Uranus and Gaia (Heaven and Earth).