At a recent installment of Twitter’s weekly all-hands "Tea Time" meeting, employees took turns sharing why they work at Twitter . One Tweep offered the reason, "Because one tweet can change the world." (Read more about that meeting, and Twitter's plans to turn itself around, in Fortune's new feature story, "Fixing Twitter.”)

That claim would sound cheesy–if it weren’t occasionally true. Even as Twitter struggles to attract new users, it’s still a platform with incredible reach. And a single tweet, especially from an influential person, can still have a big, even world-changing, impact.

1

Obama sticks up for Ahmed.

Ahmed Mohamed, a 14-year-old student in Irving, Texas, was arrested for bringing the parts of a reassembled clock to school in a suitcase. The incident ignited a national debate about racial profiling, and President Obama responded with an invite to the White House.

2

Twitter breaks the Osama bin Laden news.

On May 1, 2011, not long after the White House announced an upcoming national security address, Keith Urbahn, a former chief of staff to defense secretary Donald Rumsfeld, tweeted out what he knew. The news quickly spread across Twitter for 20 minutes before any TV news organization could confirm it. The scoop prompted a breathless declaration from Business Insider that Urban’s tweet was "Twitter's CNN Moment." Later, it came out that separately, Sohaib Athar, a Pakistan-based IT consultant, had inadvertently live-tweeted the raid on bin Laden’s compound.

(Twitter is also credited with breaking the news of Whitney Houston's death and the Boston Marathon bombing.)

3

Caitlin Jenner introduces herself to the world.

For several years now, transgender celebrities like Laverne Cox of Orange is the New Black and characters like Maura Pfefferman of Transgender have helped bring the transgender movement into the mainstream. But reality TV star Caitlin Jenner (formerly famous as Olympic medalist Bruce Jenner) is the most prominent celebrity to publicly transition. In tandem with a Vanity Fair cover, Jenner revealed her new name on Twitter.

4

The Mars Curiosity Rover reignites excitement about space exploration.

The Mars Curiosity Rover, which landed on the planet in 2012, has used Twitter to reveal many exciting discoveries–including tantalizing hints of earth-like biological life on the plane–transmitting them in the form of gifs, videos and photos.

5

Edward Snowden speaks out.

Though he now lives in near-imprisoned status in Russia since leaking classified government documents in 2013, the former NSA contractor’s tweets on privacy and government surveillance regularly shape the national conversation. Recently, he weighed in on the showdown between Apple and the FBI.

6

Citizen journalism is first to the scene for the Miracle on the Hudson.

When U.S. Airways flight 1549 landed on the Hudson river in 2009, the first view of the crash came on Twitter. It marked another example of the Twitter's value as a news service. (This happened before Twitter allowed native photo embedding; see the photo here.)

7

Hillary makes it official.

We’re using this tweet as a stand-in for the glut of election tweets of the past year. All of the 2016 presidential candidates have used Twitter to speak to supporters, announce important news, respond to attacks, and occasionally change the conversation.

8

Trump.

While all the presidential candidates use Twitter, Donald Trump's Twitter presence is unlike that of any other candidate. He uses the platform to bully his critics, and many of his Tweets–including retweets of white supremacists and fake photos of his enemies–would once have spelled doom for anyone with political aspirations. But the volume and repetition of his statements have numbed Americans to the shock we once felt at this sort of behavior.

9

The Arab Spring.

Revolutions in 2011 in Egypt, Tunisia, Bahrain and Libya used both Twitter and Facebook to communicate and organize. Social media has continued to play a prominent role, particularly during Egyptian protests in 2013 (shown above).

10

Justine Sacco cracks a regrettable joke.

An IAC PR representative with a few hundred Twitter followers cracked an offensive joke before boarding a long flight. Valleywag, a gossip blog, drew attention to the tweet, fueling an angry mob of outrage that elevated the hashtag #HasJustineLandedYet to a trending topic. The incident completely derailed Sacco's life-she was confronted in the Cape Town airport, ridiculed online, and soon after, fired. (Sacco’s offending tweet was later deleted.)

The incident showed the world the dark side of social media and caused many to rethink their participation in angry online mobs. Twitter, Facebook and other social outlets can unite people around any cause, positive or negative. Often the outrage machine moves so fast that there's no time to consider empathy, fairness or the consequences of an attack. Twitter, which values and supports freedom of speech on its platform, continues to grapple with how to address the online harassment and bullying that comes along with that freedom. CEO Jack Dorsey has made safety one of his top five priorities.

11

Black Lives Matter

Twitter continues to be a major tool for activist movements to share information, mobilize protests, and speak out against injustices. The #Blacklivesmatter hashtag started in 2013 but grew to prominence in 2015 as the movement to curb police violence gained steam. More than 41 million related tweets have been sent.

12

Oreo dunks in the dark.

Marketers still refer to this Tweet, posted during a surprise blackout during the 2013 Super Bowl, in awe. The transition from broadcast-style advertising to the conversational world of social media has been awkward, with many brands stumbling as they try to insert themselves into social media conversations. (Inevitably, some clueless brand will use a solemn holiday or news event to do some crass salesmanship. Think Kenneth Cole's tasteless promotion around riots in Cairo.) But Oreo's quick-moving tweet showed marketers just how sophisticated they need to be to win at social media.

See original article on Fortune.com

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