Answer: Space Dust

Every moment of every day, including the moment you’re reading this sentence, the Earth is quietly collecting space dust as it rockets along its orbit around the Sun. Tiny little spheres of dust, micrometeorites barely wider than a human hair, enter our atmosphere by the trillions every year.

While each one weighs next to nothing, in aggregate the total mass of all the dust adds approximately 40,000 tons of mass to the Earth annually.