TODAY | February 01, 2014
>>> in some ways, it's hard to believe that facebook is only 10 years old.
>> started off, of course, as a small idea in a college dorm room that soon exploded in more ways, keeping a billion people in touch. joelle garguilo takes a look.
>> reporter: in 2004 , "friends" came to an end --
>> this is even harder than i thought it would be.
>> reporter: the red sox won the world series for the first time in 86 years. and a little social network then called the facebook was born. it was the brainchild of 19-year-old harvard sophomore mark zuckerberg , a way to check out who was who and who was hot on campus. he talked about it exclusively with savannah guthrie in an interview airing tuesday on "today."
>> i was just really excited that we were doing it at one school. and at the time, i thought, someone needs to build a service like this for the world. i always thought that was this incredibly important thing to have happen, but i just never thought that we would be the ones to help do it.
>> reporter: well, ten years later, 1.2 billion people, yes, billion, use facebook . that's about a sixth of the world's population. it's hard to imagine a time when facebook didn't exist, when it was just a game kids played and friends were people you talked on the phone, met up with on weekends.
>> this is really good.
>> clean and simple.
>> reporter: chronicles on film, engrained in our everyday lives. sure, facebook has made breaking up harder and cyber snooping easier, but it's also saved lives. within the first hour of posting this photo, three friends telling me go to the hospital, it could be kawasaki disease .
>> reporter: changed lives.
>> i was on facebook one day and came across a new t-shirt design coming out. $7 from the sale of each t-shirt goes to charity, a different cause each week.
>> reporter: and reunited families. as facebook hits the decade mark, its users are well past that in years, a challenge the social network is facing with competition like twitter and snapchat.
>> before facebook , there really wasn't a place where you had a global directory, where each person could say this is my digital footprint on the world.
>> reporter: facebook now worth $150 billion. now, that's what friends are for. for "today," joelle garguilo, nbc news, new york.
>> worked out for mark.
>> yeah, $3 billion additional out of that.
>> not too shabby. we asked you to weigh in, finish the sentence -- i use facebook for. we loved your responses. we have a few of them to share with you now.
>> this one says "stalk exes and research co-workers. let's be honest here."
>> i appreciate the honesty on that one. who doesn't use it for that? we also hear from barbara, who said she uses it to "keep contact with special people you have met along the journey of life no matter where your journey takes you, sharing laughs and thoughts on just about everything."
>> then quickly, another one -- "answer questions by the "today" show in hopes of having my response read on the air."
>> there you go, denise.
>> worked for you.
>> you can see savannah's full interview with mark zuckerberg tuesday on "today."
>>> coming up --
>> more on super bowl commercials , i think.
>>> when that storm in atlanta