The BBC tried to organize a seismic event by having 50,000 people in one place jump at the same time. A kilometer away it registered as a .6 on the Richter scale, according to the video below by Vsauce.
What would happen if everyone on Earth jumped at exactly the same time in the same place? Would it cause an earthquake or knock earth off of its axis?
Image credit: Jorge Lascar/Flickr