How ancient collision shaped New York skyline

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One World Trade Center

Tower One of the new World Trade Center in New York was completed last month and at 541m, it now stands proud over Manhattan, the highest skyscraper in the western world.

It is a beacon of hope on this classic skyline, a symbol of modernity and a glimpse of the future. But this gleaming new skyscraper actually has roots in a long-lost world; Tower One, like all of the other skyscrapers in New York has its foundations in a past world.

Skyscrapers seem to dominate this part of New York, but look a little closer and you can see very clearly that they are actually clustered in two distinct areas: Downtown, the financial hub of this great city, and Midtown - the home of the Empire State Building.

Image caption,
Fragments of the lost land of Pangaea are now stranded in the metropolis of Manhattan

To understand how this modern skyline came to be and why these tall buildings cluster as they do, you need to look downwards instead of up.

Prof Iain Stewart, a geologist at Plymouth University, has been getting down and dirty in the foundations of skyscrapers in New York for Rise of the Continents, a new geology documentary series on BBC Two, and it is here that the clues to understanding New York's ancient past become clear.

"New York's skyscrapers are built in two distinct clusters for a very good reason, one that is buried beneath each one of them," says Prof Stewart.

Below the busy streets of Manhattan, amongst the foundations of these giants, Prof Stewart was hoping to spot a seemingly innocuous grey rock, known as the Manhattan schist.

Charles Merguerian is a professor of geology at Hofstra University in New York and an established expert in this schist and its role in New York's history. He told the programme that "geology totally controls the skyline of New York, in that the higher buildings are always found where the rock is close to the surface".

As Prof Stewart reiterated for the programme: "It's the minerals in these rocks that are really key to understanding the conditions under which they were formed. Like in a car where your various instrument clusters tell you how it is working, minerals tell us how the rock was formed, particularly at what temperature and depth."

Image caption,
The island's skyscrapers are clustered in the financial district (foreground) and Midtown (top right)

The minerals in this rock can provide clues that help explain the shape of Manhattan's skyline, but also reveal the story of America's long lost history.

Prof Stewart was keeping an eye out for a mineral known as kyanite, a beautiful blue specimen commonly seen in the Manhattan schist. "Kyanite is a key mineral to identify, we know it only forms at very deep depths and under extensive pressure," he said.

"It's like a fingerprint, revealing a wealth of information."

The presence of this mineral reveals that the Manhattan schist was compressed under incredibly high pressure over 300 million years ago.

The schist formed as a result of two enormous landmasses coming together to form a supercontinent, known as Pangaea.

This giant continent was made up of all the land on Earth, and at this time present day New York would have been very close to its centre.

As the two landmasses converged, the rocks at their margins were pushed together like an accordion, forcing mountains upwards. The Manhattan schist was buried 13km beneath this new mountain range.

"The minerals give us a very clear indication that these rocks were formed at great depths at the bottom of a mountain range," says Prof Merguerian.

Prof Stewart explains: "The former mountains of New York probably achieved heights similar to what we see in the Himalayas today - it's incredible to imagine mountains 15 times higher than the highest skyscraper on the skyline today." Being buried and compressed under such a vast mountain range has made the Manhattan schist an exceptionally hard rock.

The supercontinent that once embroiled New York was eventually ripped apart. 100 million years later, the component parts of Pangaea began their long and arduous journeys to become the continents we see today.

After this split, fragments of the lost land of Pangaea were left behind, now stranded in today's modern metropolis of Manhattan as very hard schist.

Walking through Central Park, you will see children playing, couples sunbathing and families picnicking on rocks protruding through the surface of the park.

These rocks are Manhattan schist, part of that ancient supercontinent, fragments of Pangaea left behind when the continent split. They are just glimpses of what is below the surface in abundance in Downtown and Midtown.

And it is these fragments of very hard rock that provide the perfect foundations for New York's highest buildings. Where Manhattan schist can be found very close to the surface you can build high, and so Downtown and Midtown have become home to Manhattan's tallest buildings.

Image caption,
Kyanite only forms at depth and under extreme pressures

Elsewhere the ancient continent has been eroded away, the ground cannot support such skyscrapers and the buildings are much lower in height.

"Geology totally controls the skyline of New York in that the higher buildings are always found where the rock is close to the surface," says Prof Merguerian.

Tower One of the World Trade Center is the most recent icon in New York's majestic skyline, a skyline that has become a symbol of the modern world despite its origins being rooted in a long, lost world.

"It's amazing to think that the modern city of New York has essentially been controlled by geology below and all that started with the construction of Pangaea," says Prof Stewart.

Discover more about the lost world of Pangaea and how it has affected the way we live today in Professor Iain Stewart's new documentary series on BBC 2, The Rise of the Continents starting on June 9th at 9pm. Episode 3; The Americas will air on June 23rd.

Image caption,
The Manhattan schist protrudes through the ground in Central Park