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What If Earth's Atmosphere Disappeared?
Short answer: sound and the blue sky would go first, the daytime sky would turn black, and below about 6 kPa water at body temperature boils. Heat and unfiltered sunlight change on slower clocks. Dial the pressure down below to see each step.
What happens if the air thins to a pressure you choose, all the way down to none?
Air is easy to forget because it is always there: a column of about one kilogram on every square centimetre, blue from Rayleigh scattering, loud because it carries compressional waves, warm at night because it is a blanket. Remove that column, or leave only a percent of it, and several different clocks start. Sound and the blue sky are prompt. Liquid water at skin temperature is a pressure question, not a temperature one; at very low pressure it boils, then the vapour can freeze. Unfiltered sunlight is a radiation question. None of this is medical advice, and none of it is a survival guide. It is a pressure slider with known physics attached, plus a timeline that refuses to turn a person into a plot point.
Written and checked by Aivora Digital · Last updated:
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Results update as you move the controls.
0 is vacuum. 100 is sea level today.
Your result
vacuum
surface pressure in this run
0% of 101.325 kPa
- Pressure
- 0 Pa
- Toy boiling point of water
- no stable liquid water at the surface
- Daytime sky
- black, Sun as a hard disk
- Sound
- no medium, no sound
- Below ~6.3 kPa?
- yes (phase-change threshold)
What does that mean?
Remaining pressure is zero. The sky is black in daytime except at the Sun. There is no air to carry sound. Liquid water is not stable at the surface: it would boil, and the vapour can then freeze. Unfiltered sunlight and a huge diurnal temperature swing follow. This is a physics sketch, not medical advice — it will not describe what happens to a body, and it is not a survival protocol.
At a glance
- This run0%
- Sea level101 kPa
- Armstrong-limit ballpark~6.3 kPa
Timeline
Immediate
Sky and silence
Scattering and acoustic coupling follow the remaining column. Vacuum is a black, silent noon.
Seconds to minutes
Water's opinion of the new pressure
Boiling point slides down the Clausius–Clapeyron curve. This page does not describe injuries.
Hours to days
Heat without a blanket
No thick air means poor heat transport. Days heat, nights dump energy to space, Moon-style.
Longer
Radiation and weathering
UV and cosmic rays that the column used to stop reach the ground. Surfaces age differently. Not modelled in detail.
Compare scenarios
Silence and a black noon
The speed of sound in an ideal gas does not depend on pressure, but there has to be a gas. As density falls, coupling to eardrums and to structures fades; at vacuum there is nothing to be a wave in. The daytime sky is blue because molecules scatter short wavelengths. Thin the column and noon goes dark except where the Sun sits, as it does on the Moon. Both of those are immediate. You do not wait a season for the sky to forget how to be blue.
Water, and a careful note on bodies
Boiling point falls with pressure. A Clausius–Clapeyron toy on this page tracks that curve. Around 6 kPa — sometimes called the Armstrong limit in aviation physiology — water's boiling point meets human body temperature. That is a statement about phase change, not a diagnosis. Ebullism, hypoxia and decompression are medical topics. This experiment will not prescribe, treat, or describe injuries in detail. If remaining pressure is not a vacuum, the numbers simply scale.
Heat and the unfiltered Sun
Atmosphere spreads heat and blocks a slice of ultraviolet. Without it, the surface starts to look more like the Moon's: brutal days, brutal nights, no soft twilight. Residual pressure in this model scales a qualitative greenhouse leftover; it is not a radiative-transfer code. Cosmic rays that the column currently stops would reach the ground more freely. Plants, metals and plastics would have opinions about that light. They are not simulated here.
How we calculated this
Sea-level pressure is 101 325 Pa. Remaining pressure is the slider percentage of that. Boiling point of water uses a Clausius–Clapeyron inversion with ΔHvap ≈ 40.65 kJ/mol. If remaining pressure is zero, liquid water is reported as unstable at the surface rather than as a −∞ temperature. Sound and sky remarks are qualitative with pressure. Aviation physiology is mentioned only as a named pressure threshold, not as advice. No medical protocol, no climate GCM.
Assumptions and limitations
This is a simplified estimate. Actual results depend on factors the model does not include.
This is a simplified thought experiment. It uses transparent assumptions so you can see what changes — it is not a full physical simulation of the real world.
- The remaining gas, if any, is still Earth's mix at a uniform scaled pressure.
- Boiling-point curve is a two-parameter Clausius–Clapeyron toy.
- Speed of sound is treated as irrelevant once there is no medium.
- This is not medical advice and not a description of how to survive vacuum.
- Greenhouse and UV changes are qualitative.
Sources
- NASA Earth fact sheet
Mass, radius, rotation period and orbital speed used as the baseline Earth.
- NOAA JetStream — the atmosphere
Structure and role of Earth's atmosphere.
- NIST CODATA — standard acceleration of gravity
gn = 9.80665 m/s², the conventional standard gravity (also ISO 80000-3).
Go further
Related experiments that pick up where this one leaves off.
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