How much space material lands on Earth each year?
Estimates vary, but thousands of tonnes of extraterrestrial material reach Earth every year, almost all of it as tiny dust grains rather than rocks you could hold.
It sounds alarming, but most of what arrives from space is far smaller than a grain of sand. Earth sweeps up a constant drizzle of cosmic dust and micrometeorites, particles mostly a fraction of a millimetre across, shed by comets and produced by collisions between asteroids. Because they are so small, many drift down gently rather than burning away completely.
Measuring this rain is hard, which is why published figures range widely. Some estimates based on dust striking spacecraft suggested tens of thousands of tonnes a year entering the upper atmosphere. A careful study published in 2021, which sifted particles out of clean Antarctic snow near a research station, concluded that around 5,000 tonnes of micrometeorites actually reach the ground each year. Larger meteorites, the ones that make it into museum drawers, add only a small amount on top of that in a typical year.
To put the dust figure in perspective, Earth's mass is roughly six million million million million kilograms (6 × 10²⁴ kg), so even thousands of tonnes a year is utterly negligible. Over the planet's whole 4.5-billion-year history, the steady sprinkle has added only a thin dusting compared with the bulk of the Earth.
Every so often the yearly total is dominated by one big object. The Chelyabinsk asteroid of 2013, for example, weighed something like 10,000 tonnes before it broke up over Russia, though most of it was vaporised or turned to dust. Very large impacts are rare, which is lucky for us, but over millions of years they deliver more mass than all the dust put together. Day to day, though, the space material landing on your roof is mostly invisible specks.