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When you think of natural history museums,

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you probably picture exhibits 
filled with ancient lifeless things,

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like dinosaurs

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meteroites,

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and gemstones.

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But behind that educational exterior,

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

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there are hidden laboratories 
where scientific breakthroughs are made.

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Beyond the unmarked doors,

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

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you'd find windows into amazing worlds.

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This maze of halls and laboratories 
is a scientific sanctuary

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that houses a seemingly 
endless variety of specimens.

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Here, researchers work to unravel 
mysteries of evolution,

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cosmic origins,

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and the history of our planet.

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One museum alone 
may have millions of specimens.

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The American Museum of Natural History
in New York City

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has over 32,000,000 in its collection.

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

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Scientists have logged exactly where 
and when it was found,

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and used various dating techniques 
to pinpoint when it originated.

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Repeat that a million times over,
and these plants,

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animals,

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minerals,

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fossils,

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

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and across billions of years of history.

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When a research problem emerges,

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

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

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like peregrine falcons,

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owls,

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and eagles started to mysteriously crash,

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

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were declared endangered.

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Fortunately, scientists in 
The Field Museum in Chicago

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

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They discovered that the egg shells 
used to be thicker,

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and had started to thin around the time

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when an insecticide called DDT 
started being sprayed on crops.

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DDT worked very well to kill insects,

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

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the DDT accumulated in their bodies.

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It worked its way up the food chain

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and was absorbed by apex predator birds