First Theory is the Robots are coming and taking over Humanity.
Second Theory is that The Yellow Stone Volcano could Explode. This Volcano explodes every 640,000 years. and The last time it exploded was 640,000 ago, and Where only 1,000 years overdue. that means that this Volcano Could explode any Second.
Third theory is obvious but we can be all killed by a Astriod, And a Astriod hitting early is incredibly high and theres rumors that a Atriod could hit earth on April 29 2020.
Fourth Theory is that WW3 could happen, and it almost happen. But the thing is the nukes and a nucealer war.