We generally think of the Earth as having a constant mass. On a basic level that’s true, but the Earth’s mass does change very slightly. So is it’s mass increasing or decreasing?
Earth gains mass through dust and meteorites that are captured by its gravity. If you watched the recent meteor shower you know this can occur on a regular basis. In fact from satellite observations of meteor trails it’s estimated that about 100 – 300 metric tons (tonnes) of material strikes Earth every day. That adds up to about 30,000 to 100,000 tonnes per year. That might seem like a lot, but over a million years that would only amount to less than a billionth of a percent of Earth’s total mass.
Earth loses mass through a couple of processes. One is the fact that material in Earth’s crust undergoes radioactive decay, and therefore energy and some subatomic particles can escape our world. Another is the loss of hydrogen and helium from our atmosphere. The first process only amounts to about 15 tonnes per year, but the loss from our atmosphere amounts to about 95,000 tonnes per year.
So it’s most likely that Earth is losing a bit of mass each year, but if the rate of meteors is on the higher end of estimates, then it could be gaining a bit of mass.