Recently, we asked ourselves what Facebook's biggest energy source is. Initially, we assumed it was the electricity needed to power our servers and network, but after some consideration, it turns out to be the daily input of the more than 120 million active users -- including you -- who create the content that defines our site.

The Internet is constantly reminding us of the sheer power of "people-powered" systems, drawing their strength from the active involvement of their participants. Clay Shirky, a scholar and author, has long written about this effect in areas as wide-ranging as government, education, media and entertainment.

One day while the Facebook data team was considering the full sweep of people's engagement with Facebook, we wondered what it actually takes to power the people who power our service. People spend an aggregate of more than 2 billion minutes on Facebook each day, contributing content and staying in touch with their friends and families and typically spend between 1 and 2 calories per minute while resting at their computers.