Mary L. Gray is a Principal Researcher at Microsoft Research and Faculty Affiliate at Harvard University's Berkman Klein Center for Internet and Society.

Using the tools of anthropology and critical media studies, Mary explored how material conditions and everyday uses of technologies transform people's lives, particularly in places where technological access is hard to come by.

I invited Mary onto the Tech Talks Daily Podcast to talk about her book "Ghost Work: How to Stop Silicon Valley from Building a New Global Underclass," which she co-authored with computer scientist Siddharth Suri. In the book she explores the lives of people paid to train artificial intelligence and, increasingly, serve as "humans in the loop" delivering on-demand services.

Hidden beneath the surface of the web, lost in our wrong-headed debates about AI, a new menace is looming. I learn how services delivered by companies like Amazon, Google, Microsoft, and Uber can only function smoothly thanks to the judgment and experience of a vast, invisible human labor force.

These people doing "ghost work" make the internet seem smart. They perform high-tech piecework: flagging X-rated content, proofreading, designing engine parts, and much more. An estimated 8 percent of Americans have worked at least once in this "ghost economy," and that number is growing. They usually earn less than legal minimums for traditional work, they have no health benefits, and they can be fired at any time for any reason, or none.

There are no labor laws to govern this kind of work, and these latter-day assembly lines draw in--and all too often overwork and underpay--a surprisingly diverse range of workers: harried young mothers, professionals forced into early retirement, recent grads who can't get a toehold on the traditional employment ladder, and minorities shut out of the jobs they want.