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There is meteoric material falling on the Earth constantly, as well as some protons and other light nuclei from the solar wind as well as from cosmic rays.

At the same time Earth's atmosphere looses gas to space, especially the lightest elements like hydrogen and helium.

Does one process dominate the rate of change of Earth's mass? Is Earth getting heavier or lighter?

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tl;dr: The Earth receives 40,000 tons of dust from space every year, but looses 95,000 tons of Hydrogen and 1,600 tons of Helium every year as well. After all additional effects are balanced, the Earth looses about 50,000 tons a year.


It seems a similar question was asked in Astronomy Stack Exchange, and this short answer links to the BBC News article Who, What, Why: Is the Earth getting lighter? which answers this question.

There are factors that are causing Earth to both gain and lose mass over time, according to Dr Chris Smith, a medical microbiologist and broadcaster who tries to improve the public understanding of science.

Using some back-of-the-envelope-style calculations, Dr Smith, with help from physicist and Cambridge University colleague Dave Ansell, drew up a balance sheet of what's coming in, and what's going out. All figures are estimated.

By far the biggest contributor to the world's mass is the 40,000 tonnes of dust that is falling from space to Earth, says Dr Smith.

Surprisingly, General Relativistic effects of Global Warming is considered!

Nasa has calculated that the Earth is gaining energy due to rising temperatures. Dr Smith and his colleague Mr Ansell estimate this added energy increases the mass of Earth by a tiny amount - 160 tonnes.

Using $E=mc^2$ that works out to about $1.4 \times 10^{22}$ Joules/year or $4.6 \times 10^{14}$ Watts. That's about 3.6 Watts/meter^2 or about 0.3% of the total power coming from the Sun, so it does seem to be back-of-the-envelope-in-the ballpark correct!

But there is something else that is making the planet lose mass. Gases such as hydrogen are so light, they are escaping from the atmosphere.

"Physicists have shown that the Earth is losing about three kilograms of hydrogen gas every second. It's about 95,000 tonnes of hydrogen that the planet is losing every year.

"The other very light gas this is happening to is helium and there is much less of that around, so it's about 1,600 tonnes a year of helium that we lose."

So taking into account the gains and the losses, Dr Smith reckons the Earth is getting about 50,000 tonnes lighter a year, which is just less than half the gross weight of the Costa Concordia, the Italian cruise liner, that ran aground recently.

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    $\begingroup$ I wonder if the mass loss associated to radioactive decay is a significant contributor to this mass balance. Also, we might be loosing Hydrogen, but there is also a shower of alpha particles coming from the Sun, and those are hydrogen nuclei. I wonder is such effects were taken into account. Interestingly, with those numbers it might not bee too far in the future the time when human created mass gains and losses (though space exploration and extraterrestrial mining ) will be grater than natural ones. $\endgroup$ – Camilo Rada Apr 13 at 15:55
  • $\begingroup$ @CamiloRada these are good points. Energy stored in the nucleus (before decay) and energy deposited and stored as heat (after) will have the same mass. It's only the total energy of the Earth that counts, so it's just the heat in versus heat out. Radioactive decay is steady but global warming is the sudden change. $\endgroup$ – uhoh Apr 13 at 16:43
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    $\begingroup$ Not really. Because the energy produced by radioactive decay have already created a temperature gradient that carries that energy out to the surface and is then radiated to space. Effectively been lost. Otherwise the temperature of Earth's would be rising. $\endgroup$ – Camilo Rada Apr 13 at 16:50
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    $\begingroup$ @CamiloRada oh you're indeed right. Heat due to radioactivity is (eventually) radiated into space and therefore represents a continuous loss of mass. $\endgroup$ – uhoh Apr 13 at 16:57

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