You are a time traveler. Your mission was originally to travel back only 10 years, but you accidentally end up in the dinosaurs era. Not only that, but you crash into an asteroid. This is the same asteroid that annihilated the dinosaurs, and it turns out it was YOU that sent it towards earth in the first place.
You crash land on the earth and the asteroid is not far behind. You must now navigate through the savage and primal pre-historic world and find the missing parts to your time machine before the asteroid hits the earth.
Your only weapon is a make-shift time gun, that can send any living being to a random point of time or accelerate/decelerate the growth of vegetation.