Earth's Atmosphere -- Is gravity the reason we have air pressure?

[shiva bhargav]

TL;DR Summary

gravity pulling the atmosphere

I have read an article in Quora, where a person says that "Gravity pulls the atmosphere towards itself and that's one of the reason why our Atmosphere is still this way" and also adds that, "gravity is the reason we have air pressure in the first place. Gravity pulls on the atmosphere, compressing it, and creating pressure. " Is it true? if so, my question is even the other planets have a gravity pull yet our scientists say they don't have proper atmosphere as do we have.

 

[russ_watters]

Summary: gravity pulling the atmosphere

I have read an article in Quora, where a person says that "Gravity pulls the atmosphere towards itself and that's one of the reason why our Atmosphere is still this way" and also adds that, "gravity is the reason we have air pressure in the first place. Gravity pulls on the atmosphere, compressing it, and creating pressure. " Is it true?

Yes.

if so, my question is even the other planets have a gravity pull yet our scientists say they don't have proper atmosphere as do we have.

Smaller planets have less gravitational pull and more trouble holding on to an atmosphere.

 

[shiva bhargav]

Yes.

Smaller planets have less gravitational pull and more trouble holding on to an atmosphere.

But there are bigger planets too comoared to ours why aren't we able to detect proper atmospheric conditions there which we need

 

[jim mcnamara]

Our atmosphere is a derived one. It started out as poisonous. Later, small primitive single celled life (cyanobacteria or blue green algae) "invented" photosynthesis. Photosynthesis over about 2 billion years or more changed our atmosphere into one with oxygen. The atmosphere of Earth before oxygen arrived would kill most complex living things today. Like other planets.

Those primitive cells are still around today and live in shallow seas in formations called stromatolites. You can also see them in pond scum.

The time when free oxygen started to appear environment has several names, I like: Great Oxygenation Event
https://en.wikipedia.org/wiki/Great_Oxidation_Event
Note that free oxygen is toxic to many kind of primitive organisms, so they have to live places where there is no free oxygen.
Examples: meromictic basins (https://en.wikipedia.org/wiki/Meromictic_lake) , or in layers of mud at the bottom of lakes or oceans with oxygenated waters, or some deep caves.

 

[russ_watters]

But there are bigger planets too comoared to ours why aren't we able to detect proper atmospheric conditions there which we need

"Proper atmospheric conditions" is a lot different than just having an atmosphere; all of the larger planets have significant atmospheres (and the gas giants can basically be said to be mostly atmosphere).

Gravity is why we have an atmosphere, but as Jim says, what makes it good for us is more complicated.

 

[Genava]

Summary: gravity pulling the atmosphere

I have read an article in Quora, where a person says that "Gravity pulls the atmosphere towards itself and that's one of the reason why our Atmosphere is still this way" and also adds that, "gravity is the reason we have air pressure in the first place. Gravity pulls on the atmosphere, compressing it, and creating pressure. " Is it true? if so, my question is even the other planets have a gravity pull yet our scientists say they don't have proper atmosphere as do we have.

Gravity is giving the weight of all the matter above your head. This is the same situation deep in the ocean, you are feeling the pressure from the water column above but this pressure depends also on the gravity (density of the water).

However, it is also related to the quantity of matter in the atmosphere. Think about Venus in regards of the Earth. So atmospheric pressure depends on the gaseous state of the matter at the planet's surface.

Furthermore, there is a relationship between the ability of a planet to retain its atmosphere, its gravity/mass and its proximity to the star.

 

[Irbis]

I think that problem is more complex. Gravity plays its role in holding mass on any planet, but the density of gases, their segregation, temperature variation with altitude, geomagnetic field and proximity to any other cosmic object are also important. Starting with gravity, it is known that it differ from sea level to e.g. 2000 km altitude. Solar wind can strip planets from its atmosphere if there is no magnetic field protection. That's why Mars lost its atmosphere. On the other hands water vapors and carbon dioxide are heavy and are staying to the bottom of the atmosphere ( which is good for plants), while hydrogen and helium because are light are staying at the top, where the pressure is low, the gravity is much lower and the solar winds has powerful impact. That's why there is so little helium quantity in Earth atmosphere. I think that Earth lose every year some mass of atmosphere gases into the space, and I will like to know the amount and the composition. Still there is a balance with what happening on the Earth surface. There are intense addition of gases due to life activity, volcanoes activity (just one volcano can add gasses more than the gases added by humanity along all its existence), industrial activity, cattle growing and mainly poor waste management. The atmosphere become denser, but still lose lighter gas components in space.

 

[Eskcanta]

That's why there is so little helium quantity in Earth atmosphere. I think that Earth lose every year some mass of atmosphere gases into the space, and I will like to know the amount and the composition.

Atmosphere escape is one term for the phenomenon.

"Atmospheric escape of hydrogen on Earth is due to Jeans escape (~10 - 40%), charge exchange escape (~ 60 - 90%), and polar wind escape (~ 10 - 15%), currently losing about 3 kg/s of hydrogen.[1] The Earth additionally loses approximately 50 g/s of helium primarily through polar wind escape. Escape of other atmospheric constituents is much smaller.[1] A Japanese research team in 2017 found evidence of a small number of oxygen ions on the moon that came from the Earth.[10] "

https://en.wikipedia.org/wiki/Atmospheric_escape

 

[Vanadium 50]

However, it is also related to the quantity of matter in the atmosphere. Think about Venus in regards of the Earth. So atmospheric pressure depends on the gaseous state of the matter at the planet's surface.

Exactly. Another example is Mercury vs. Mars: nearly identical surface gravity, but one has an atmosphere and the other for all practical purposes does not.

The title says "the reason". There is no one reason. Gravity is necessary but not sufficient.

 

[Genava]

On the other hands water vapors and carbon dioxide are heavy and are staying to the bottom of the atmosphere ( which is good for plants)

In the case of water vapor, it has nothing to do with molecular weight, but this is due to the Clausius Clapeyron relation. The dependence with temperature mostly.

Moreover in the case of CO2, the concentration decreases sharply only above 80 km on Earth, so it is not "at the bottom". As Eskcanta pointed out about helium and hydrogen, this is not only due to molecular weight.

volcanoes activity (just one volcano can add gasses more than the gases added by humanity along all its existence)

A single volcano?

 

[Irbis]

A single volcano?

I do not know if it is correct to say a volcano, as well as an earthquake of 13 degree magnitude on Richter scale, while there were produced by a meteor impact with Earth, and it ends a geological era. I saw some debates on this subject.

 

[jim mcnamara]

@Irbis : the Richter scale is not used anymore. And a magnitude 13 (which does not exist on the new scale) earthquake is impossible on any of the smaller planets. It would require a fault the circles the Earth or Mars more than 100 times. So it has no meaning in this context. And it is not defined in the scale anyway.

Since you cannot have read this anyplace that PF requires to validate statements like yours, please refrain from making stuff up. Thank you.

 

[jim mcnamara]

Since this thread is going astray it is time to cut off any more hot air. Thread closed.