On this day in history - March 21

What Happened On This Day – March 21

• 2006 Jack Dorsey sends the world's first Twitter message, or tweet

  The microblogging service revolutionized the communication and social networking landscape. In 2012, about 340 million tweets were posted per day.

• 1985 South African Police kill at least 21 black people commemorating a similar mass shooting 25 years before

  The Sharpeville massacre in 1985 had left 69 unarmed people dead. It was a turning-point in the history of South Africa.

• 1970 Earth Day is celebrated for the first time

  The first edition was limited to some cities in the United States. Today, Earth Day is observed by about 1 billion people around the world.

• 1952 The world's first rock and roll concert is held in Cleveland, Ohio

  DJ Alan Freed presented the concert, which was closed down after only one song because of over-crowding.

• 1943 A plot to assassinate Adolf Hitler by suicide bomb fails

  German Wehrmacht officer, Rudolf von Gersdorff, failed to blow up the dictator but managed to defuse his bombs just before they went off and avoid suspicion.