2006: Co-founder Jack Dorsey tweeted first, when the service was called “Twttr.”
2007: Early user Chris Messina proposed the use of a hashtag to denote people at the same live event.
2008: When the Mars Phoenix Lander found ice on Mars, NASA used Twitter to break the news.
2009: Early user Janis Krums happened to be on a ferry when a plane went down in the Hudson River.
2009: Ashton Kutcher was the first person on Twitter to reach 1 million followers.
2010: Astronaut TJ Creamer sent the first tweet from space, marking an historic moment in social media.
2010: In a royal first, the Prince of Wales’ private office announced Prince William’s engagement to Kate Middleton.
2011: Up late one night, Sohaib Athar inadvertently live-tweeted the raid on Osama bin Laden’s compound in Pakistan.
2011: Beyoncé announced she was pregnant with her first child, setting a record of 8,868 tweets per second.
2012: President Obama noted his second presidential win. And within hours it became the most retweeted for the year.
2012: Pope Benedict was the first Pope to join Twitter, creating 8 accounts to tweet in different languages.
2013: Two bombs shook the Boston Marathon – and the world. Twitter became crucial for journalists, police and citizens.
2013: The passing of revered South African statesman Nelson Mandela flooded Twitter, spiking at 95,000 tweets per minute.
2014: Ellen DeGeneres' Oscar selfie was retweeted over 3.3 million times, breaking the record held by POTUS.
2014: The #BringBackOurGirls movement was created when more than 250 schoolgirls were abducted in Nigeria.
2014: The World Cup was the biggest sports event, with more than 672 million tweets during the month-long tournament.
2015: Caitlyn Jenner joined Twitter and reached 1 million followers in 4 hours, breaking the record held by POTUS.
2015: As the horrific attacks in Paris unfolded, the world united to support people in the City of Light with #PrayForParis.
2016: Leonardo DiCaprio's Oscar win sparked a spike of 440,000 tweets per minute, breaking Ellen's selfie record.
https://blog.twitter.com/2016/thank-you-love-twitter