Today, specifically at 3:50pm ET, it will mark the very first tweet on Twitter made by @jack, Jack Dorsey, co-founder of Twitter. It was made on March 21st, 2006 at 3:50pm eastern time and it said "just setting up my twittr".

Since then, Twitter has grown to 50 million tweets per day and it has become an internet phenomenon. People stay in touch with other people, with the news, and even celebrities on Twitter. So, Happy 4th Birthday Twitter, with best wishes to continue moving forward.