Eons

If you were to climb Mount Everest, you might find something remarkable in the rocks under your boots: fossils from the bottom of an ocean.

Beneath your feet would be tiny fragments of trilobites, crinoids, and other critters that lived in a shallow sea, more than 400 million years ago, during the Ordovician Period.

And yet, today, this is the roof of the world, the highest point above sea level on Earth.

This reveals just how dramatic the story of the Himalayas is.

As one of the greatest geological features on the planet rose up, it reshaped the land in incredible ways.

But the rise of these mountains affected more than just the immediate area.

Turns out, we may have the Himalayas to thank for everything from the rise of giant flightless birds in Madagascar; to the disappearance of plants from Antarctica; to the expansion of the great grasslands of North America, and more.

The story of the Himalayas starts in the Ordovician, around 485 million years ago.

Back then, the area that would become Tibet and the Himalayas was part of the Paleo-Tethys Ocean.

The ecosystem was dominated by suspension-feeders, with clam-like brachiopods and sea lilies snagging food from the passing current.

Cephalopods and early jawless fish probably also swam nearby.

But although this area started as an ocean, it wouldnt stay that way.

During the early Mesozoic Era, the collision of several small crustal fragments drove the lifting up of the land thats now Tibet though exactly how that process unfolded is still debated.

Then, suddenly or, well, very, very gradually, depending on how you perceive geologic time, something appeared on the horizon.

It was the Indian subcontinent, drifting northward.

As it came closer to the continental land mass, geological forces pushed up what would become the Tibetan plateau and Himalayas even higher.

And by about 55 million years ago, in the Eocene epoch, the Indian and Eurasian plates collided for real.

Of course, you cant just slam two continent-sized plates together without some significant local effects.

Up until that point, the area that would become the Himalayas was dominated by tropical forests full of plants like fig and ironwood.

Meanwhile, farther north, Central Asia was already arid thanks to that Mesozoic uplift.

By the Oligocene Epoch, 34 million years ago, the ecosystem of that drier region was made up of conifers and other plants adapted to a shift to colder temperatures.

And rodents and lagomorphs, like rabbits and pika, thrived there, as they could digest the hardy, less nutritious plants.

But as time went on, the rising mountains reshaped things.

And not just in terms of pushing land higher in elevation, though that was a factor.

While some kind of monsoonal system probably existed in the region before, as the mountains reached 4,000 meters, they began to form a large rain shadow.

Rain shadows happen when moisture-laden winds coming in from the ocean are pushed up by the mountains.

There, the air expands and cools, causing water to condense out as rain.

The result was a massive amount of rain on the windward side of the mountains.

And by the Miocene Epoch, 23 million years ago, the monsoons were as strong as we see today.

To the south, where the tropical fig-filled forests dominated, the rising elevation pushed the ecosystem into a new, colder climate.

For some species, like plants suited to colder conditions and altitudes, including oaks, plums, and maples, this created a new corridor that they could spread into.

But for others, this ecological break-up created new barriers.

And these separations became even more distinct as the mountains rose higher.

Combined with the increasingly numerous rivers eating away at the rock and carving deep valleys between peaks, this break-up divided the landscape into different niches like grasslands, tundra, montane forests, dry forests, and rainforests.

And the plants and animals that lived there, now isolated from their neighbors, began to diversify.

This is especially evident in plants.

The Himalayas today have over 4,000 endemic species of flowering plants.

But we also see this extreme diversification in animals, too, like reptiles, amphibians, butterflies, fishes, and freshwater crabs.

In the meantime, while the southern side of the mountains was being carved out by the monsoons, on the northern side of the plateau, the Himalayas and their massive rainshadow were further drying out Central Asia.

This would soon give rise to great deserts like the Gobi, along with diversification in some groups of desert-loving plants and animals, like the scorpions in the Miocene.

(Give it up for the scorpions, I guess).

So the landscape and ecosystems around the Himalayas were changing dramatically.

But, if some scientists are right, the Himalayas might have been changing the rest of the world, too.

And to see how, we need to rewind a little bit.

Back in the Eocene, some 55 million years ago, much of the world enjoyed a warm, humid climate.

But as time went on, that warm, wet world started to steadily cool down into the Miocene 23 million years ago.

This global cooling could be linked to a decrease in carbon dioxide concentrations in the atmosphere, which weakened the global greenhouse effect.

And as for what caused the carbon dioxide levels to drop, that brings us back to the Himalayas.

In the late 1980s, an environmental scientist teamed up with a planetary scientist to propose that this cooling could have been caused by the mountains and the monsoons.

The idea is that all that newly exposed rock, lashed by those monsoon rains, may have supercharged a process called chemical weathering.

Ok, heres how that works: When raindrops form in the atmosphere, a small amount of carbon dioxide gets dissolved and trapped in those droplets.

This turns the carbon dioxide into carbonic acid, making the entire raindrop slightly acidic.

When these slightly acidic raindrops fall to Earth, the carbonic acid can chemically react with surfaces they touch, including rocks which creates bicarbonate ions that wash out to sea.

Once that happens, the ions are taken up by shelled organisms like diatoms that eventually die and fall to the sea floor.

This puts carbon into a kind of long-term storage, reducing atmospheric carbon dioxide overall.

This process is usually balanced out by other factors, like carbon dioxide being emitted from erupting volcanoes.

But the key is that its a balance one that the rising Himalayas may have upset.

The vast amounts of newly-exposed rock, combined with monsoons bringing in carbonic acid to carve through them, may have pushed carbon dioxide levels to new lows.

Now, the exact details of this process and how much cooling we can lay at the feet of the Himalayas is still debated.

But if this was the major source of the cooling, then that means the Himalayas affected not just the Asian landscape, but also some pretty distant ones.

Take Antarctica, for example.

By the middle of the Miocene, 14 million years ago, it was a relatively cool place with widespread glaciers and tundras, like what you might find in northern Canada today.

But the Miocene cooling helped kill off most of that vegetation as it put the continent on permanent deep freeze.

Meanwhile, on the coasts of the Northern Pacific Ocean, that same cooling may have helped kelp diversify and spread into great off-shore kelp forests.

This formed a rich feeding ground for marine creatures like sea cows.

And as things cooled down, they also dried out in many places.

The late Miocene saw the birth of the Sahara Desert in Africa, for example.

But one of the biggest transitions was the disappearance of tropical and subtropical forests in parts of Africa, Europe, and North America.

Which probably led to the extinction of the once-diverse apes in Europe.

Much of those forests were replaced by new grasslands, like North Americas great plains, the African savannah, and the Eurasian steppe.

The grasses that dominate these ecosystems use C4 photosynthesis, a particular pathway that does better in low carbon dioxide conditions and arid environments than the alternative, called C3 photosynthesis.

Meanwhile, the colder temperatures and abundant grasslands may have enabled horses and paleognath birds, like ostriches, emus, and the now-extinct moas to grow bigger over time.

So in the end, the Himalayas didnt just shape the geography of Asia, but also potentially the path of evolution around the world.

When we think of the Himalayas, we tend to think vertically.

But, as weve seen, their power also stretches out in other directions.

It stretches far back in time, as a landmass once home to everything from Ordovician sea critters to lush, tropical, fig-filled forests to modern yaks, snow leopards, and other animals adapted to the extreme cold and elevation.

It reaches deep, as the mountains created varied habitats and impassable rifts and barriers that have been both a haven and an engine for biodiversity.

And it reaches wide.

From the monsoons of Southeast Asia to the Gobi Desert.

From the frozen ice sheets of Antarctica to the great grasslands of the Americas.

The Himalayas may be big, but their effect on life on Earth may have been even bigger.