Until now, scientists didn't know how much of this cosmic dust was gathering on Earth (though they know rather a lot about how much is up in space). Researchers guessed that anywhere between 0.4 and 110 tons of the star stuff entered our atmosphere every day--that's a pretty wide range. But a recent paper took a closer look at the levels of sodium and iron in the atmosphere using Doppler Lidar, an instrument that can measure changes in the composition of the atmosphere. Because the amount of sodium in the atmosphere is proportional to the amount of cosmic dust in the atmosphere, the researchers figured out that the actual amount of dust falling to the earth is along the lines of 60 tons per day.