Life After People Page #5

Structures out here

Don't so much decay

When you live them alone;

They melt.

these structures

On black island, Maine

Used to be part

Of granite quarry whose stone

Was used to build and decorate

Cities like Boston, New York,

And Philadelphia.

It was abandoned around 1920.

here, the buildings

Have all vanished

Within the space

Of 80 and 90 years.

There's almost nothing left.

in the right conditions

And with human maintenance,

Stone construction can last

For thousands of years.

In some places in Europe,

Ancient roman aqueducts

Are still in use.

But without maintenance,

Stone can fall victim

To a very stealthy enemy.

one of the great enemies

Of stone are actually salts

And salt crystals.

Even thousands of years ago,

People notice the effect

That salts had on deteriorating

The ancient pyramids.

there are many ways

Salts infiltrate stone buildings

And monuments:

Polluted air, seawater,

And even bird droppings.

soluble salts dissolve

In water,

And as the water evaporates,

It will rise up inside

Of porous building materials;

Things like brick and stone

And even concrete.

And what happen are the salts

Will continue to grow

Inside the pores of the stone

Until they come up

Against the side of the wall,

And they'll actually push

The stone apart.

what we're seeing

In this time-lapse video

Really shows the rapid decay

Of the stone in response

To this deterioration by salts.

In this experiment,

It took about three weeks to go

From this piece of stone

To this piece of stone,

Which is completely deteriorated?

By sodium sulfate

Crystallization.

three weeks in this

Accelerated aging chamber

Are equivalent to a few years

In the harshest of environments,

Or a few decades in a more

Benign desert climate.

if we could see

Microscopically what's going on?

Inside the pyramids,

This is what

Would be taking place.

You can actually see the salts

Deteriorate the stone.

although not immune to decay,

The pyramids have survived

For nearly 5,000 years

Because of their sheer volume

And their hot,

Dry desert environment.

Too massive to be destroyed

By either man or nature,

The pyramids of Giza

Were the only one

Of the seven wonders

Of the ancient world to survive

Into the modern era.

Many ancient monuments

Have survived only

Because of human maintenance

Throughout the centuries.

The sphinx was uncovered

And restored for the first time

Back in 1400 back.

Modern experts who have studied

The sphinx, predict

That without human intervention,

Deterioration from salts

And wind erosion could render it

A pile of dust

Within 500 to 1,000 years.

The largest concrete structures

Like hover dam, will last

Even longer than that.

Hover is so thick

That over 70 years

After it was constructed

The concrete deep inside

Was still curing.

But of the 15 tallest dams

In the United States,

Only 10 are concrete.

The others are made of compacted

Rock or earth,

Like northern California's

Trinity dam.

If there were humans around,

This leak in the dam would get

An emergency fix.

But those days are long gone.

some of these dams

Are absolutely enormous.

And if they fail,

As they will in time,

Then the surge of water

That falls in behind them

And cascades

Down a valley below

Would have a huge force,

Big enough to sweep away

Everything on its path.

fifty years after humans,

The strain of neglect

Is beginning to show

On even the best design

Of manmade structures.

everything that man designs

Carries within it, the seeds

Of its own destruction;

That includes bridges

And buildings.

The Brooklyn Bridge,

One of the most famous bridges

In the world for over 125 years.

The reason

Those bridges last so long

Is because engineers

Look after them.

They inspect them regularly,

They maintain them,

They paint them,

They replace pieces that need

To be replaced.

Without people,

Without engineers,

The deterioration process

Will accelerate dramatically.

the most vulnerable parts

Of a suspension bridge

Are the steel vertical hanger

Cables.

these have been tested

In the laboratory,

Unfortunately not on the bridge,

But what you see

Is a classic kind of a failure?

That occurs in these wires.

These are the individual wires,

All right?

That's an individual wire.

That probably has

A tensile strength

That's maybe 200,000 pounds

Per square inch.

That's a very high strength

Steel.

as strong as they are,

These cables have a fatal flaw:

It's the stuff they're made of.

steel is a mineral

That comes from the earth

That's mostly iron,

So it's probably

95, 98 percent iron.

exposed to moisture

In the environment,

Iron will start to revert

Back to the minerals

It came from.

Ashes to ashes, dust to dust.

it's going to go back home.

It came from the earth

As iron oxide of some form,

And it's going to go back.

this is the process we know

As corrosion,

And you see it wherever steel

Is exposed to moisture.

the enemy of steel

Is corrosion.

The problem

Is keeping the water out.

Part of that is maintenance.

If you don't maintain them,

You will get corrosion.

completed in 1883,

The Brooklyn bridge cost

$15 million to build.

Over the last two decades,

$3 billion have been spent

Maintaining it

And the other bridges

Over the east river.

In the time of humans,

The Brooklyn Bridge

Was continually maintained

And fully repainted,

Roughly, every dozen years.

While across the country

In San Francisco,

The golden gate bridge

Was protected at all times

By a vigilant brigade

Of 17 iron workers

And 38 painters.

what do they do all the time?

They will tell you, "We paint

This bridge continuously."

What happens when that stops?

I can tell you what happens

When that stops.

The cables begin to rust,

The paint peels off,

The wires begin to break,

And they'll come to a point

When the bridge

Is going to come down.

seventy-five years

After people.

Most of the 600 million cars

That once traveled the roads

Of the world

Are now just rusted remnants

Of the human past.

abandoned cars will behave

Differently depending

On the environment

That they're in.

A car left in the Mojave Desert,

For example,

Is going to last a long time.

A car abandoned

In my native Scotland

Is going to have

A very different fate.

Any cars

In a coastal environment

With salt in the atmosphere,

They might not last

More than 20, 30 years.

tires deflate

Within a few years,

Although the rubber

And synthetics they're made of

Will remain intact

For centuries.

Paint deteriorates quickly.

And once it flakes away,

Rust corrodes the car's body

At a rate of 5,000ths

Of an inch per year.

Seventy-five years after humans,

Most cars,

Even in the most forgiving

Of environments,

Will be reduced to skeletons.

After a century, the family car

Is a barely recognizable heap

Of metal.

It's now 100 years into a life

After people.

The Brooklyn Bridge,

Which had stood?

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