Is the Earth gaining or losing mass over time? The earth presumably loses mass because molecules of the atmosphere disassociate and fly off into space where the solar wind carries them away.
On the other hand the earth gains mass because particles of dust and meteorites strike the earth and accumulate onto it.
Which force is dominant? Does the earth gain mass over time or lose mass?
 A: We really don't know the figures of mass loss, or mass gain through cosmic dust accumulation.
Mass loss through Hydrogen and Helium 

According to some calculations, the Earth is losing 50,000 tonnes of mass every single year, even though an extra 40,000 tonnes of space dust converge onto the Earth’s gravity well, it’s still losing weight.

If you take the lower end of the mass accumulation estimation from cosmic dust, that is 5 metric tonnes daily, this results in a figure of 1825 metric tonnes a year, resulting (if you take 50,000 tonnes a year of $\mathrm H_2$ and $\mathrm{He}$  as accurate), in a definite answer that the Earth is losing mass. 
A break even figure for mass equilibrium is 137 tonnes of comic dust daily, which is almost midway between the (widely differing) estimates of 5 to 300 tonnes of cosmic dust thought to fall on Earth daily.
Cosmic Dust Estimates

Even though we consider space to be empty, if all the material (cosmic dust mainly) between the Sun and Jupiter were compressed together it would form a moon 25 km across.
  Satellite observations suggest that 100-300 metric tons of cosmic dust enter the atmosphere each day. This figure comes from the rate of accumulation in polar ice cores and deep-sea sediments of rare elements linked to cosmic dust, such as iridium and osmium.
  But other measurements – which includes meteor radar observations, laser observations and measurements by high altitude aircraft — indicate that the input could be as low as 5 metric ton per day.

The answer is we really don't know, but as we seem to have more accurate figures on mass loss than mass gain, it seems we can have more confidence that Earth has a net mass loss.
A: There's indeed mass loss from atmo loss, and 
mass gain from (micro)meteor..
But there's more at work than that..
Mass regain from atmo regain
And neutron absorption (and other single atoms) as a direct result
from solar radiation..
The atmo regain is part of the atmo loss when the atmo particles
fall back to Earth again, if they didn't have enough initial speed under a certain vector to leave the earth's gravity.
the neutron and proton radiation also adds weight..
As part of the sun's radiation, they get blasted towards earth as well..
Most of them that hit the earth's magnetosphere get deflected..
But not all..which are the neutrons mostly..
Natural background radiation..
neutron's get absorbed into earths large mass
And also a few proton's here and there..
Then there's another thing, natural proton annihilation, decaying into energy, and I think there's neutron decay as well, also into energy..
So..is the earth gaining weight or losing it ?
I think it's gaining weight, contrary to popular belief..
(the atmo loss calculations are off since atmo regain wasn't calculated in..)
Also, if the atmo had been losing out on that much for 2B years, it would be
atmo-less now..(or at least significantly less..)
(since the top part is mostly H, and still exists..)
The highest layer is H mostly, and therefore would be hit the hardest,
and therefore the most to escape..
However 2B years of de-hydrogenisation @ 50 Kilotonnes/year..
- slowly counts..
100 Teratonnes of H loss..
So, I guess that would make the H layer either really thin, or negatively non-existent..
(unless someone says the total tonnage of H in the upper layer >100 teratonnes..I didn't bother to look it up..)
Also, over time the magnetosphere increased in strength, while
in the beginning it was relatively weak..
As the Earth grew more dense, and the metal layers started shifting in height,and moved in a circular fashion, and cooled down, decreasing the
average distance between particles (through compression etc)
it became closer and closer to what it is today..
I think measuring it's strength would yield interesting results..
(or rather the change in it..)
As the magnetospehere increased in strength, so did the protection
against solar radiation for Earth and once the solar winds
couldn't touch much of the planet's atmo anymore it stabilized..
Although atmo loss occurs, it also falls back..
Also, any (micro)meteors that hit earth's surface or lower atmo,
keep adding stuff that never leaves..the solar winds can't blast
it enough to make it escape..
the only thing we have to worry about is the earth's core
getting too solid, in which case the magnetosphere's strength
goes down again, and umm..well general badness..
(hence me suggesting checking the strength of the magnetosphere.)
-still does not want to do complex math..
