We need to talk about the biggest break-up of   all-time: the break-up of  the supercontinent Pangea.

Around 200 million years ago, the  ground split open, and the crack   grew until it reached all the way across the  supercontinent, eventually flooding with seawater.

This seaway connected two ancient oceans together,   separating Laurasia in the  north from Gondwana in the south.

And it also separated all the  plants and animals that lived on each.

This was a major fork in the road of evolution.

Life became divided into two different groups.

But they didn’t lose touch forever.

The subcontinent of India became  a sort of island messenger between   the two halves of the globe, breaking  away from Gondwana and traveling 9000   kilometers across the sea  to collide with Laurasia.

This journey took 35 million years, but the plants  and animals that went along for the ride when   India became an island eventually reunited with  their long-lost northern relatives…kind of.

Because a lot can happen over that much time.

And, ultimately, when India smashed  back into Asia it really just traded   one form of evolutionary isolation for another.

When the break-up started, Gondwana was made up of   what is now South America, Africa,  India, Antarctica, and Australia.

Africa, Madagascar, and India were once neighbors.

That is, until sometime around  120 to 100 million years ago,   when a rift formed, breaking India  and Madagascar away from Africa   and isolating all the Gondwanan  plants and animals living there.

Then, around 90 million years ago,   Madagascar split off and India  was basically on its own.

Now, we know that island isolation often  leads to unique evolution.

Think of the Galapagos,  or Madagascar itself for that matter.

This is allopatric speciation, where a physical   barrier creates a separation  that leads to new species.

And during the Cretaceous period, the  island of India was home to a bunch   of animals that were suddenly cut  off from the rest of the world… Everything from frogs, lizards, turtles,   snakes, centipedes and crocodiles to  plant-eating sauropods like the gigantic   Jainosaurus and meat-eating theropods like  the two-legged Indosuchus and Rajasaurus.

There were even early   mammals like Gondwanatheres, an extinct  group that looked kinda like big rodents.

But Cretaceous life on India wasn’t all an island   paradise, as the subcontinent was  just beginning a wild tectonic ride.

When it first broke away, it was  traveling at around 5 centimeters per year.

That’s already pretty fast.

Today,   the average plate moves at  around 1.5 centimeters per year.

And India was so fast because  it’s very thin…only 100 km thick   compared to other plates like Africa at 300 km.

The gigantic plume of hot material  that had emerged from the mantle   and caused the initial breakup of Gondwana  had also melted rock off of India’s base.

And then, 80 million years ago, the plate   accelerated to a sprint, moving at a  rate of over 14 centimeters per year.

This is because it was being pulled by two  parallel subduction zones, where one plate   slides beneath another and sinks into the mantle.

One of these was in the middle of the Tethys   Sea and the other was along  the coastline of Laurasia.

Because they both pulled in  the same direction, like two   people on the same side of a tug of war,  this yanked India northward exceptionally fast.

India then sped through different  climates, putting pressure on the   plants and animals to adapt  to new conditions or perish.

Around 67 million years ago, the plate began to   slide over the Réunion hotspot, fueled  from below by a massive plume of magma.

And the force of this plume beneath  the Indian plate sped up its pace even more.

It also triggered a massive  volcanic eruption known as the Deccan Traps.

This was a flood basalt - erupting  lava literally flooded the Earth’s surface.

It poured out enough lava to  cover an estimated 1.5 million   square kilometers - an area the size of Mongolia.

This amount of lava could fill  the Great Lakes nearly 50 times over.

Today, the remaining basalt still  covers 15% of modern India.

And this volcano came at the worst possible time.

Because one of the main eruptions lasted  700,000 years, and began just 300,000 to   400,000 years before the Earth was  hit by the asteroid that led to the   Cretaceous-Paleogene extinction  66 million years ago.

And while the Deccan Traps didn’t cause   this extinction, many scientists think  they played a big role in worsening it.

The eruption spewed out toxic gasses like mercury.

It also released aerosols that spread out in the   atmosphere, reflecting sunlight  and suddenly cooling the planet.

But when these cleared, the carbon  dioxide released by the same eruption   also warmed the planet over the longer term.

The temperature had come back  down by the time the asteroid hit,   but this roller coaster of climate meant that  life was already under incredible stress.

And in addition to feeling these  global effects, life on the island   of India also had to contend with  lava flows and nearby volcanic gasses.

Living basically right on top of the Deccan Traps   meant that the effects of the  mass extinction were amplified.

Nearly all vertebrates were  wiped off the subcontinent.

The few survivors included frogs, snakes,  caecilians, the worm-shaped amphibians.

All of these can burrow into the  ground for protection, so that   might have been the key to surviving both  a massive volcano and an asteroid impact.

After the dust settled, there’s about  a 10-million-year gap in our understanding.

Paleontologists just haven’t found many  fossils from this time in India.

So we pick up the story again during the  Eocene, around 55 million years ago.

And the fossils from this time  make it clear that the island   of India played an important role in  the evolution of placental mammals.

But where did these mammals come  from in the first place?

One idea is that they could  have originated in Gondwana   and survived the Cretaceous-Paleogene extinction  in India…known as the ‘Out-of-India’ hypothesis.

But most scientists disagree.

See, India broke away before mammals  with placentas evolved.

And since the vast majority of modern mammals,   including all modern Indian mammals–  have placentas, the ancestors of these   mammals would need to have somehow  made it to the island of India.

So researchers think that, despite  being in the middle of the Tethys Sea   at the time, it’s more likely that  India wasn’t completely isolated.

As the subcontinent neared the Asian mainland,   but before it had fully docked, some animals  were able to migrate from the mainland to India.

They likely did this by hitching a ride on   floating objects or jumping between  smaller islands like stepping stones.

And once these mammals made it, ancient India was  home to some big evolutionary milestones.

In fact, both horses and whales can  trace their roots back there.

For a long time, the evolutionary history   of Ungulates – mammals with  hooves – wasn’t well understood.

See, fossils of both groups of  ungulates - those with an even   number of toes and those with an odd number  - appear suddenly across multiple continents.

So where they came from in the first  place has been a big question for a long time.

And a study from 2014 describing a   54.5-million-year-old fossil of Cambaytherium  in India provided an interesting clue.

This was a genus of four-legged  herbivores that was an ancestor to the   order of Perissodactyla, the odd-toed ungulates.

Today this order includes horses and rhinoceroses.

So this entire order could have originated  in India as it was nearing a collision with Asia.

But what about the even  toed ungulates, called artiodactyls?

This group includes pigs, giraffes, and  camels, as well as whales and dolphins   known as cetaceans, who evolved  from land-dwelling mammals.

And Indohyus was one of these mammals.

Indohyus looked kind of like a deer with  a long nose, and thin limbs with hooves,   but it was around the size of a cat.

Its fossils have been found almost exclusively  in India and Pakistan, suggesting this is   where cetaceans made their transition  from land to sea during the Eocene.

And each stage of this transition can  be seen in Indian fossils.

That is, until 49 million years ago, when   the protocetids – a group of  extinct cetaceans – evolved.

Then suddenly their  fossils appear all over the world.

Cetaceans had gained the ability to spread  out from the island, across the world’s oceans.

Their ability to swim gave them a head start  in terms of spreading out from India.

But the collision with Asia provided a burst of  new land-based species in both directions.

India fully established a connection to the  mainland around 45 million years ago, which is   when we see plants and animals begin migrating  both out of and into the subcontinent.

One of these groups was the Dipterocarps, a family   of trees that can grow to over 50 meters tall  and today dominate Southeast Asian rainforests.

They originated in Gondwana during   the mid-Cretaceous and were  carried across the sea by India.

And some animals, like the ungulates,  originally came from Asia, but   continued their evolution on the island of  India before dispersing out again.

Others, like the blindsnakes, centipedes and  caecilians, first originated on Gondwana,   survived the mass extinction  and diversified in India before   spreading out across Asia –  after a very long ferry ride.

And the rate at which species migrated back   and forth from India to Asia continued  to increase until 15 million years ago.

Because, while India’s isolation and  journey across the sea was a unique   tectonic moment that led to the evolution  of equally unique animals, it wouldn’t   be the last time geologic forces isolated India… Its collision with Asia built the  tallest mountains in the world: the Himalayas.

And just like oceans, mountains  create barriers between groups   of species, allowing them to evolve in isolation.