865 million years ago, a collision shattered a city-sized asteroid. Like a building demolition, boulders flew apart as dust blanketed the area. Under the sun's warmth, the fragments drifted slowly until Jupiter's gravity hurled them toward Earth, the Moon, and Mars.

The bombardment shook Earth: shockwaves released carbon dioxide, disrupting the ocean's carbon cycle and altering marine life. The Moon gained more craters, and volcanoes on Mars stirred to life. Scientists tell the fragments apart by their reflected light (spectroscopy, the Fraunhofer method) and brightness (photometry); they were once mistaken for comets. Traces of that ancient cosmic dust still settle today. And analysis of Bennu revealed amino acids — perhaps such impacts seeded Earth with organic material.