The sky is falling. Every day, around 160 tons of rubble rain down on us. 

Most of it originated in the vast cloud of dust and gas that gave birth to the solar system more than 4.5 billion years ago. At first, budding planets and asteroids were formed by material swept up from this cloud. As our solar system matured, chance collisions between the asteroids caused them to spiral into chaotic orbits and crash into planets.

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