Facebook Milestones Leading to a Billion Daily Users

— -- When Mark Zuckerberg launched Facebook from his Harvard dorm room in 2004, his audience was college students.

Today, more than 1 billion people log onto Facebook every day. The social network first hit the one billion mark in August, but the momentum has continued. Facebook revealed in its third quarter earnings report Wednesday that it now has an average of 1.01 billion daily active users. That means 1 in 7 people on the planet are checking Facebook every day.

"A billion users is a landmark and symbolic number that tech investors are laser-focused on, as we witnessed when Apple broke the magical billion iOS devices sold earlier this year," Daniel Ives, managing director of the technology, media and telecom research group at FBR Capital Markets, told ABC News. "The billion milestone carries a lot of weight among tech investors on the street."

Even Zuckerberg didn't foresee how big Facebook would become.

"People often ask if I always knew that Facebook would become what it is today. No way," he reflected on Facebook's 10th anniversary on Feb. 4, 2014. "I remember getting pizza with my friends one night in college shortly after opening Facebook. I told them I was excited to help connect our school community, but one day someone needed to connect the whole world."

Here's a look at some of the key moments and milestones that helped Facebook build its user base.

2004: The site was intended as a directory of Harvard students only, but within months, thousands of students from elite colleges across the country had joined the network.

2006: Open registration launches, letting anyone join the social network and create a profile. The newsfeed feature also launched this year, letting people get instant updates on their friends.

2008: The Facebook app makes its debut.

2012: Facebook goes public with a $5 billion IPO.

2015: Facebook continues to innovate with new ways for people to engage with the world. Among them are video calling in the Messenger app, easy-to-read instant articles and a live-streaming feature that gives users a front row seat to the latest happenings from their favorite celebrities and news makers.