Well it's like with the Collider they just got running not too long ago. There was some worry that if it worked it could rip the fabric of the universe apart, or cause the Earth to implode. Scientists agreeing on any one possibility is kind of a rarity.
This is the first thing I thought of after looking at the OP's post
Strangelets, sound cute, don't they? Well they're responsible for turning every atom they touch into "strange matter" (sounds like the makings of a new mario game) and from this they expand, and absorb, and as long as they keep coming into contact with atoms, they could essentially turn the entire planet into a..strange, umm, husk? I guess :/
But for better or for worse, this theory has also been discredited, and the collider deemed safe enough for satisfying scientific curiosity
But it's broken for now, and I feel alot safer for it ^_^