Tethys Suture

    Earth is a dynamic living planet with a churning heat engine that continually reshuffles its materials and repaves its surface. The Indian region is a spectacular result of this ongoing metamorphosis. We are lucky to learn about these changes through our sojourns at sea and on land, and in the incredible diversity of landscapes, ecosystems, and cultures in the region.

Thousands of miles below our feet, Earth’s iron core and mineral mantle drive heat to the surface through a slow churn of solid rock over millions of years. This convective conveyor belt gradually pushes the continents and ocean basins around in a process of continental drift also known as plate tectonics. 

Over the past 200 million years, the continents of Earth’s Eastern Hemisphere have been assembled through a series of progressive collisions as landmasses moved from south to north. The deep south-to-north conveyor pushed continents together and dragged heavier ocean crust downward into the underlying mantle, leaving the largest landmasses in today’s world. 

Siberia and Scandinavia hosted Europe and Central Asia and then Africa and India docked somewhat later. Each of these great gatherings consumed ocean plates, which now dangle thousands of miles below like tattered draperies. Each suture or seam is a crumple zone, where solid rock was smushed together into massive folds and gigantic west-to-east mountain ranges from the Atlantic to the Pacific. 

Much of our voyage will be an exploration of this great suture zone where once the Tethys Ocean lapped the shores of Laurassia and Gondwana. From the Atlas Mountains of Morocco, along the Alps, to the roof of the world in Central Asia, to the volcanic ridges of Indonesia, the Tethys Suture divides the Old World into northern and southern domains. The Mediterranean is a tiny remnant of the former glory of the Tethys Ocean. 

The west-east vastness of the Old World was built in long stages, forming globe-spanning ecozones that allowed evolving plants and animals to flourish across broad latitude zones. This in turn encouraged emerging humanity to spread pastoral and farming practices and our associated cultures along the natural grain of Earth’s surface. Boreal  forests stretch from Norway across Siberia. Dappled summer sunlight filters through leafy deciduous canopies from the Lime trees of Ireland across to Shinto shrines of Japan. Vast grasslands are home to herds of hoofed mammals, nomadic pastoralists, and horse-riders across 12 time zones from Spain to Manchuria. Sun-scorched sands stretch from the Sahara to the Gobi, with seasonal savannas and teeming tropical forests further south.

Conversely, the closing of the Tethys Suture produced nearly insurmountable east-west mountain barriers that separate life zones, ecosystems, and human cultures to this day. Unlike the north-south mountain ranges that split the Americas, catastrophically crumpled mountain chains of Central Asia wall off the frigid and parched interior from the hot wet Indian subcontinent. India and China host nearly a third of humanity, and their histories and cultures have interacted for millennia. Yet the very distinct cultures of these close neighbors owe much to the mountain fastness that divides them, combined with the forbidding deserts to the west and jungles to the southeast.

India was a late arrival to the Tethys Suture. The Indian Plate swept rapidly up from the deep south, with subduction swallowing the intervening ocean starting around 70 million years ago. By 55 million years ago, compression had formed huge chains of volcanos and mountain belts as the ocean basin closed. India “docked” with the Asian mainland around 10 million years ago but the slow catastrophe in ongoing. The greatest mountain ranges on Earth wrap around the leading edge where India plows deep into central Asia. These ranges wrap around Iran, Afghanistan, Pakistan, Tibet, Nepal, and Southeast Asia. They structure climate, hydrology, vegetation, food supply, and culture over a vast region affecting billions of people.

Roof of the World

The Himalayas form the southernmost and highest boundary of the great continental crumple zone that resulted from India’s collision with Asia. The name is derived from Sanskrit hima “snow” alaya “abode.” The chain is composed of many smaller ranges and reaches above 8000 meters (26,000 feet, 5 miles) elevation in places. 

The Himalaya and related mountain chains drastically alter the climate of Asia. The highest mountains are indeed covered with snow and ice, hosting enormous glaciers. Monsoon winds push tropical moisture up from the south where it falls in seasonal torrents, yet to the north of the great mountain barrier the land is parched and bare. 

The Himalayan foothills are lush and wet with seasonal rains, eroded into complex systems of rugged canyons and valleys. They were densely forested in ancient times, but large areas have been cleared for farms and pastures.