When you think of natural history museums,

you probably picture exhibits 
filled with ancient lifeless things,

like dinosaurs

meteroites,

and gemstones.

But behind that educational exterior,

which only includes 
about 1% of a museum's collections,

there are hidden laboratories 
where scientific breakthroughs are made.

Beyond the unmarked doors,

and on the floors 
the elevators won't take you to,

you'd find windows into amazing worlds.

This maze of halls and laboratories 
is a scientific sanctuary

that houses a seemingly 
endless variety of specimens.

Here, researchers work to unravel 
mysteries of evolution,

cosmic origins,

and the history of our planet.

One museum alone 
may have millions of specimens.

The American Museum of Natural History
in New York City

has over 32,000,000 in its collection.

Let's take a look at just one of them.

Scientists have logged exactly where 
and when it was found,

and used various dating techniques 
to pinpoint when it originated.

Repeat that a million times over,
and these plants,

animals,

minerals,

fossils,

and artifacts present windows into times
and places around the world,

and across billions of years of history.

When a research problem emerges,

scientists peer through these windows
and test hypotheses about the past.

For example, in the 1950s, populations
of predatory birds,

like peregrine falcons,

owls,

and eagles started to mysteriously crash,

to the point where a number of species,
including the bald eagle,

were declared endangered.

Fortunately, scientists in 
The Field Museum in Chicago

had been collecting the eggs 
of these predatory birds for decades.

They discovered that the egg shells 
used to be thicker,

and had started to thin around the time

when an insecticide called DDT 
started being sprayed on crops.

DDT worked very well to kill insects,

but when birds came 
and ate those heaps of dead bugs,

the DDT accumulated in their bodies.

It worked its way up the food chain

and was absorbed by apex predator birds