Why hasn't the air pressure of Earth dropped?

The Earth loses oxygen, water, and a variety of other material to space every year. Why hasn't the air pressure dropped?

Earth’s atmospheric mass hasn’t dropped noticeably because the losses are negligible and the reserves are vast. Per Atmospheric escape - Earth is primarily losing 3kg/s (95,000 tons/year) of hydrogen, with negligible amounts of other gases.

Regardless of the atmospheric reservoir of hydrogen, Earth’s main hydrogen reservoir…

Why hasn't the air pressure of Earth dropped?

…is 1.35 billion cubic kilometers of water. That’s 1.35 billion, billion tons of water, which contains 0.15 billion, billion tons of hydrogen.

At 95,000 tons of hydrogen lost per year, Earth has lost only 1/3,157th of its hydrogen to space in the last 4.5 billion years due to Jean’s Escape Mechanism, solar wind sputtering, and other effects. It would take another 14,206 billion years (at the sun’s current brightness and activity) to dry out most of Earth’s hydrogen. Of course, by then the sun will have gone through a red giant phase, eaten Earth, and atmospheric loss will be a secondary issue.


Loss rates of gases other than hydrogen drop exponentially with molecular mass. We’re losing 1,577 tons of helium per year. Oxygen and nitrogen loss rates are much smaller.

So, basically, Earth’s atmospheric pressure hasn’t dropped due to atmospheric loss because of:
  1. Earth’s gravity
  2. Earth’s enormous reserves in gases
  3. the slow loss rates of those gases

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