What was the biggest creature ever to exist on Earth?

Question: What was the biggest creature ever to exist on Earth?
- Keywords:
  creature,
  earth,
  size
Asked by 11mccoa1 to Josh, Stuart on 28 Jun 2013.
- Stuart Archer answered on 28 Jun 2013:
  
  The blue whale is thought to be the biggest animal that’s ever lived on Earth – the biggest ones can grow over 30 meters long and weigh over 190 tonnes!

Question: What was the biggest creature ever to exist on Earth?