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When you think of natural history museums,

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you probably picture exhibits [br]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 [br]about 1% of a museum's collections,

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there are hidden laboratories [br]where scientific breakthroughs are made.

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Beyond the unmarked doors,

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and on the floors [br]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 [br]is a scientific sanctuary

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that houses a seemingly [br]endless variety of specimens.

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Here, researchers work to unravel [br]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 [br]may have millions of specimens.

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The American Museum of Natural History[br]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 [br]and when it was found,

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and used various dating techniques [br]to pinpoint when it originated.

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Repeat that a million times over,[br]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[br]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[br]and test hypotheses about the past.

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For example, in the 1950s, populations[br]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,[br]including the bald eagle,

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were declared endangered.

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Fortunately, scientists in [br]The Field Museum in Chicago

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

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They discovered that the egg shells [br]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 [br]started being sprayed on crops.

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DDT worked very well to kill insects,

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but when birds came [br]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