Marissa Mayer poses at Google's Mountain View, California headquarters in this February 24, 2009 file photo. (NOAH BERGER/REUTERS)

Emily K. Schwartz is an assistant editor at WaPo Labs, the digital team at the Washington Post Company focused on innovation and experimenting with emerging technologies.

A week ago, few people would have considered Yahoo to be in the same league as Amazon, Facebook, or Google. The company has fared as a meager remnant of the glorious tech boom of the late 1990s, and for years has struggled under a revolving-door of management. As innovation in the Valley quickened, Yahoo was left in the dust. Their future was questionable.

All of that changed Monday.

In what is perhaps the coup of all coups, Yahoo announced Marissa Mayer, a Google executive of 13 years, would be leading their company as chief executive officer starting immediately. She would begin the job while pregnant. If the Internet’s reaction to this historic move is in any way a reliable indicator, Yahoo made a phenomenal decision.

Here are three reasons why:

First and foremost, the board decided to put a pregnant woman in charge of a company. Ask yourself, would your company have made the same decision? Probably not. But this is not unprecedented for Yahoo. The company has shown confidence in women in the past, tapping Carol Bartz as CEO in 2009 — although her tenure was brief. But Mayer is different. She has flown more or less under the radar, slowly and steadily building the experience needed to deliver and impress. She is credited with Google’s famous white search page, Gmail layout, and Google Maps design. She has an eye for product design, and a history of successful decision-making. Pregnancy? Not an issue. Mayer knows her stuff.

That brings us to reason number two: Yahoo needs someone who knows their stuff more than ever. In reacting to the news on Twitter, some wondered why Mayer would choose to go down with the Yahoo ship. Does she really think she can save the fledgling tech company? Yahoo thinks she can.

Finally, Yahoo is setting a remarkable precedent. Since Sheryl Sandberg delivered her oft-cited 2010 TED talk on why there are too few women leaders, the world has been abuzz about how to get more women pursuing STEM careers. Meg Whitman, CEO of Hewlett-Packard, and Sandberg, COO of Facebook, have been two of tech’s most outspoken female stars. When Sandberg was named the first female to Facebook’s board earlier this year, cheers broke out. When news broke of Mayer’s move to Yahoo on Monday, the cheers were even louder.

Here’s why this is significant. Today, only 18 percent of students studying engineering in the U.S. are women. Though women comprise 47 percent of the total labor force, they make up only 25 percent of the STEM workforce. If you look at Sun Valley’s annual Allen & Co conference this year, the roster of 624 tech, business, and media moguls included sixteen women. Sixteen. That’s an embarrassing number — an inexcusable number.

Yahoo’s coup in hiring Mayer isn’t significant because of the change in power — it is significant because it reflects and promotes the notion that women can be powerhouses in the tech sector.

There are companies that would have shied away from hiring a pregnant woman to turn around their brand. By putting their entire business — indeed, their trust — in Mayer’s hands, Yahoo is telling the world that they have confidence not only in Mayer as a woman, but in what she represents. They have stepped up to the plate.

Yahoo has made it more difficult for other companies to ignore the too-few-women-in-tech problem. Facebook may have been the most prominent company to launch a woman into their higher ranks, but Yahoo’s decision has been decided with a heavier, unexpectedly progressive hand.

They are thinking differently. They are ready to experiment. Watch them closely, because this move signals they are angling towards bigger, better things.

Read more news and ideas on Innovations and read more by Emily Schwartz at WaPoLabs .