Earth's atmosphere is leaking into space.

Great, as if we didn't have enough to worry about... From Universe Today:

Oxygen is constantly leaking out of Earth's atmosphere and into space. Measurements taken by satellites during the 1980s and 1990s showed the escaping ions were traveling faster the higher they were observed. This implied that some sort of acceleration mechanism was involved. Now, new work on data collected by a group of formation-flying satellites called Cluster shows that Earth’s own magnetic field is accelerating the oxygen away. But don't worry, compared to the Earth’s stock of the life-supporting gas, the amount escaping is negligible. However, in the far future when the Sun begins to heat up in old age, the balance might change and the oxygen escape may become significant.