Twitter released a video Thursday to celebrate the service's seven years of existence, reminding viewers of some of the biggest tweets and topics of the past seven years, including co-founder Jack Dorsey's initial test of the network, the service moving to Japan, and first tweets from Oprah Winfrey and from space. "Since Dorsey posted that first tweet, Twitter has become one of the world's most important communications platforms," writes Daniel Terdiman, pointing to the network's 400 million daily tweets and 200 million active users.