This is 99% invisible. I'm Roman Mars.

In 2014, President Obama expanded the Pacific Remote Islands Marine National Monument,

making it the largest marine preserve in the world at the time.

The Pacific Remote Islands Marine Preserve is farther from human settlement than any other U.S. territory.

The President's expansion of the reserve today will close

49,000 square miles of largely undisturbed ocean to commercial fishing and

underwater mining. And if you look at a map, the preserve really is nowhere near the United States.

It's thousands of miles from the U.S. mainland.

That's reporter Emmett Fitzgerald.

It's not even that close to Hawaii. Yet somehow President Obama was able to protect this piece of ocean in the name of the United States.

And to understand how the United States has jurisdiction over these waters in the middle of the Pacific Ocean, we've got to go all the way back to the 19th century,

when for a brief period, U.S. sailors scoured the oceans looking for rocky islands covered in guano.

Which a lot of people think of is just bat poop.

I think most people think of guano as bat poop, but in this case we're talking about birds and seabirds.

So seabird poop.

That's Paul Sutter.

I'm a professor of history at the University of Colorado at Boulder.

In the mid-1800s, the United States

became obsessed with the quest to find and sell guano to use as fertilizer on farms.

People believed it would revolutionize farming, and it did, at least for a little while,

but the quest for bird poop ultimately had even bigger ramifications.

The use of sea bird poop as fertilizer starts in South America.

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