It was the biggest event in our planet’s history since the extinction of the dinosaurs.
Three million years ago, the Americas collided.
The creation of the Panama Isthmus – the narrow land bridge that joins the two continents – wreaked havoc on land, sea and air. It triggered extinctions, diverted ocean currents and transformed climate.
Now a multi-billion dollar project to widen the Panama Canal is set to reveal new secrets about the event that changed the world.
Panama is a tiny country, but in a perfect location.
Positioned just north of the equator in the Caribbean, its famous canal is the strategic hub of the global shipping industry.
The 80km (50-mile) -long Panama Canal, completed in 1914, connects the Atlantic and Pacific oceans. Its existence means that ships can avoid – at a price – the treacherous 8,000 mile journey round Cape Horn, the southernmost tip of South America.
Three years ago work began to widen the Panama Canal for the first time in its history. Authorities hope that this will increase revenue from shipping.
However, the massive excavations have also proved to be a “gold mine” for scientists, trying to uncover Panama’s hidden past
One of those fossil hunters is Aldo Rincon, a young student with sharp eyes. Last year, he stumbled upon one of the most important discoveries so far: the jaws and bones of horses, rhinos, and camels.
Clash of civilizations
Dr Bruce MacFadden, an expert on fossil mammals at the University of Florida, US, explained: “When the Americas collided about three million years, it caused of a kind of land rush”.
“Animals that were native to North America – sabre-toothed cats, horses, camels and elephants – surged south across the land bridge. Animals from South America such as giant sloths and armadillos, moved north”.
In an ecological experiment on a scale never before seen, the animals of two continents freely mixed. Unable to compete with the waves of invaders, some species on both continents went extinct.
The event helped shape the ecology of the Americas to this day.
However, Aldo Rincon’s new discovery muddies the water. The animals that he has found were all natives of North America, but 17 million years old – dating from long before the Great American Interchange.
They show that the Panama Isthmus may have started to form much earlier than previously thought, allowing some migrants into Central America.
Other fossil discoveries have also hinted at this possibility.
Dr MacFadden said: “Giant predatory birds dubbed ‘terror birds’ seem to have migrated from between the Americas as early as five million years ago.”
“It is possible that long before the seaway finally closed, a chain of islands spanned the gap. Perhaps Terror Birds and other animals were the original ‘island-hoppers’, migrating from one island to the next.”
The formation of the Panama Isthmus, however, did not only affect the Americas. It also transformed global climate, and might even be responsible for the UK’s dismal and damp summers.
Dr Pierre Sepulchre, a climate scientist at the Pierre-Simon Laplace Institute, France, told BBC News: “When the Panama Isthmus formed, ocean currents got re-routed.
“Warm Caribbean waters that had once flowed through the gap between the Americas were now forced northwest towards Europe, creating the Gulf Stream.”
Without the Gulf Stream, the UK would have a freezing climate like that of Newfoundland on the east coast of Canada.
But there were other even more dramatic effects as well.
“Its controversial,” said Dr Sepulchre, “but some scientists think that the formation of the Gulf Stream transported extra moisture into the Arctic atmosphere. This fell as snow, triggering the build up of the Greenland Ice Sheet.”
In turn, this may have kick-started the Ice Age.
So, the formation of a tiny land bridge in one remote part of the tropics seems to have triggered a ‘domino effect’ that influenced the whole world.
More on: BBC