Asteroids!

In this post, meteors, asteroids, and comets are interchangeable.

Throughout history, meteors have hit earth, or have passed near earth. With the advent of the nuclear bomb, new preventions were discovered, and earth was safer. Yet most people are against the use of nuclear weapons to protect earth from an even greater catastrophe.

This catastrophe has already killed off the dinosaurs, if one of the current theories is to be believed. However, asteroids are what allow humans to exist: Comets brought the water on earth to earth, meteors brought rare metals, and asteroids added to the landmass of earth.