This is 99% Invisible.

I'm Roman Mars.

When I look at a body of water, I assume that it's teeming with microbes.

And for that reason, I wouldn't fill my water bottle from a puddle or a pond or probably even a stream,

because I know that I have a chance of getting a waterborne disease.

But I don't apply the same scrutiny to the air I breathe, which is a little odd because it too

is chalk full of life. Scientists call it the aeroboom. It's this huge ecosystem that we really barely understand at all.

This is science writer Carl Zimmer, who has written an amazing new book called Airborne,

all about the life that is wafting about in the air all around us.

The aerobium is not just important for how nature itself works,

but you are breathing in living things pretty much with every breath.

You know, most of the time they don't kill you.

But, you know, when you have a pandemic, sometimes a lot of people do die.

Carl Zimmer's book is a scientific history of the air and its relationship to disease.

I started reading the book for fun, but I decided to interview Carl on the show because it actually has a lot to do with architecture.

Most of our breathing happens indoors, and yet modern architects rarely design buildings with airborne disease in mind.

Carl Zimmer thinks that's in part because for over a century, scientific institutions have been reluctant to take the air seriously as an important vector for disease.

We got a taste of this during the early days of the COVID-19 pandemic, when there was a lot of conflict and confusion about whether the virus was airborne,

and what airborne even means.

But this conflict and confusion, it didn't start in 2020.

I mean, the fact is that our struggle to understand the air and what the air means to us and our health

actually goes back

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