They identified a total of 1,280 unmelted micrometeorites and 808 cosmic spherules (melted space rock) below 350 micrograms in mass, which allowed them to calculate the rate at which these particles rain down on the surface.
From this, the team extrapolated that roughly 80 percent of the cosmic dust that reaches Earth's surface is ejected from comets as they zoom by on their orbital journeys - a number consistent with previous estimates of the cometary input to space dust on Earth.The team's models, however, also showed that the total mass of cosmic dust input before atmospheric entry is around 15,000 tons.Figuring out which of these it is, the researchers said, could help us better constrain the role of cosmic dust in delivering water molecules and carbon to Earth, in the early days of the Solar System - in turn providing pieces of the puzzle that is the emergence of life itself.