1. The Arab Spring tweet.
“Welcome back Egypt #Jan25”

 On January 25, Google marketing manager Wael Ghonim was released after being held captive for 12 days by the authorities in Cairo. He became a symbol of the Arab Spring movement after tweeting:  “Welcome back Egypt.”

He later said: “I’m not a hero. The real heroes are the youth who are behind this revolution. By God’s will, we’re going to clean this country of this rubbish.”

 2. The Osama bin Laden death tweet.
“Helicopter hovering above Abbottabad at 1AM (is a rare event).”

Sohaib Athar, an IT consultant tweeted when he noticed a helicopter hovering overhead on May 1, during the middle of the night. This was the first report of the US Navy Seal raid which ended in the death of al Qaeda mastermind Osama bin Laden.

 3. The father daughter reunion tweet.
“my daughter her name is sarah m. rivera”

A New York homeless man called Daniel Morales was reunited with his daughter after years apart after sending this tweet. He had been given a phone by an organisation called Underheard, which helps give a voice to homeless people.

3. The impromptu NBA game tweet.
“This lockout is really boring..anybody playing flag football in Okc..”

During a standoff between NBA basketball players and the sport’s authorities over money, Kevin Durant, 23, a forward with the Oklahoma City sent this tweet and showed up to play with the man who replied.

 4. The London riots tweet.
“Brooms up London!”

In response to the London riots this August, a mass clean-up was organised in areas such as Clapham. @riotcleanup notched up more than 70,000 followers and the above tweet typified the effort.

5. The space shuttle Endeavuor tweet.
“Here’s another Photo of the shuttle from my plane.”

In May, 33-year-old Stefanie Gordon was flying to meet her mother in Florida when she looked out of the window to see the space shuttle Endeavour blast past her into space. The photo she took rapidly went viral.

6. The Japanese tsunami tweet.

On March 11 an 8.9 magnitude earthquake and tsunami devastated Japan, this tweet was sent by many who found themselves in the path of destruction.

7. The lip reading tweet.
“Subtitles are always so bad.”

In protest at the poor quality of subtitles for televised football matches, lip reader Julia Probst tweeted an alternative version in November; publishing what the players and coaches said during games.

8. The Turkey earthquake tweet.
“Ercis central mosque behind the apartment building…”

After the earthquake in Van, Turkey, in October, this tweet led to the rescue of two people buried in rubble.

 9. The Mortons steak man tweet.
“Hey @Mortons – can you meet me at the newark airport with a porthouse when I land in two hours?”

In August 17, Peter Shankman sent this tweet as a joke, as he flew back to New York. Amazingly, when he arrived at Newark a tuxedo-clad waiter holding a steak was waiting for him.