11
$\begingroup$

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?

$\endgroup$
5
$\begingroup$

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.

$\endgroup$
  • $\begingroup$ The Atmospheric Loss reference is specific to water; hydrogen and helium experience significant loss rates... $\endgroup$ – DJohnM Dec 9 '16 at 16:24
  • 1
    $\begingroup$ This answer is incorrect. Most estimates are that the Earth is losing more mass via atmospheric losses than it gains via cosmic dust, etc. The error bars on both are however rather large. What is correct to say is that both the current mass loss and mass gain are extremely tiny when compared to the mass of the Earth. $\endgroup$ – David Hammen Dec 9 '16 at 16:55
  • $\begingroup$ @DJohnM my sincere apologies for misunderstanding your point in your earlier comment. I had no idea that 1, The light elements are so relatively common in our atmosphere and 2. Such a large proportion of them have escape velocity. I have reversed my answer in light of your comments and those of David above. $\endgroup$ – user108787 Dec 9 '16 at 17:45
  • $\begingroup$ The rotational rate of the earth is slowing over time and so its rotational kinetic energy is decreasing. And since mass is energy, mass is also being lost by the slowing. Probably not nearly as much as the net gas/dust loss. The energy would need to be comparable to $c^2$ $\endgroup$ – docscience Dec 9 '16 at 21:20
  • $\begingroup$ @docscience about the same order of magnitude as this question : ) and we could keep fit physics.stackexchange.com/questions/296110/… $\endgroup$ – user108787 Dec 9 '16 at 21:25
-1
$\begingroup$

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..

$\endgroup$
  • $\begingroup$ There are numerous errors in this answer. The Sun doesn't emit significant numbers of free neutrons, but even if it did, they would almost all decay long before they reached Earth. It does emit neutrinos, but their mass is negligible, and they mostly pass straight through the Earth. $\endgroup$ – PM 2Ring Aug 29 '18 at 15:59

protected by Community Apr 4 '18 at 10:47

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.