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 wouldn’t stay that way.

During the early Mesozoic Era, the collision of  several small crustal fragments drove the lifting   up of the land that’s 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 can’t 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, here’s 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 it’s 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 America’s 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 didn’t  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 we’ve 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.