The hashtag #5secondsofsummer trended worldwide for the first time on Twitter.
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Justin Bieber made his first tweet at 8:27 pm, promoting his single 'One Time.'
Chris Messina Tweeted #barcamp, which became the first use of a hashtag on Twitter.
Twitter was launched to the public.
Justin Bieber reached one million followers on Twitter.
The Australian boy band 5 Seconds of Summer formed.
