<p>It won't be (and isn't) zero. To see that, you want the plot on a logarithmic scale. Thus there isn't really a question to answer. The attenuation of cosmic rays will follow some exponential decay with airmass. Since most of the airmass is at low altitudes then that is where most of the attenuation takes place. The Earth's magnetic field is also a factor, which is why there is a latitude dependence.</p>
<p>Here's a similar diagram but with a logarithmic dose scale (<a href="http://koreascience.or.kr/article/JAKO201017337337120.page" rel="noreferrer">Hwang et al. 2010</a>).</p>
<p><a href="https://i.sstatic.net/yBobI60w.png" rel="noreferrer"><img src="https://i.sstatic.net/yBobI60w.png" alt="Dose vs altitude" /></a></p>

CC BY-SA 4.0
2024-06-13T04:39:19.700Z
I would imagine there's also some latitude dependence due to oblateness of the atmosphere.
Cadence
CC BY-SA 4.0
2024-06-13T07:35:45.317Z
I'm not convinced that 0.001 is significantly different from zero, or that "the air mass is at low altitudes is where most of the attenuation takes place", since the highest slope on the chart is around 40,000 feet
wepajakeg
CC BY-SA 4.0
2024-06-13T08:41:05.447Z
@wepajakeg A vertical slope on that figure means *little or no attentuation*, since the amount of cosmic rays isn't changing with altitude. *Strong* attenuation happens when the slope is closer to horizontal: as you go down in altitude, the number of cosmic rays you can detect goes down (a lot).
Peter Erwin
CC BY-SA 4.0
2024-06-13T14:26:34.913Z
If I'm reading this correctly, the muon and photon curves (and, just barely, the electron and neutron curves) fold back on themselves at higher altitudes.  Is there an obvious reason for this, or should I make it a new question?  My own best guess is secondary radiation from proton (or unmentioned) collisions in the stratosphere.
Cristobol Polychronopolis
CC BY-SA 4.0
2024-06-13T15:04:06.183Z
@CristobolPolychronopolis Yes, it's secondary radiation, and yes, you should make a new question.
zwol
CC BY-SA 4.0
2024-06-13T18:19:24.187Z
@Peter Erwin but the problem is why the air density reaches the necessary density close to the surface. If the amount of air in earth were random, it should most probably be reached at higher altitude, or below sea level (not reached).
wepajakeg
CC BY-SA 4.0
2024-06-13T20:39:59.687Z
@wepajakeg The graph shows that there is nothing special about sea level. What do you mean by "necessary density"? If you go to lower altitudes (assuming you could dig a big hole), the effective dose rate would keep going down exponentially.
WaterMolecule
CC BY-SA 4.0
2024-06-13T23:17:16.833Z
@WaterMolecule The special thing about sea level (and a few kilometers above)  is that 98% or so of the lethal cosmic radiation has been absorbed. The logarithmic scale shows that it is never zero but the absolute scale shows clearer that it is "good enough" for us. Which is no coincidence, if only for the anthropic principle.
Peter - Reinstate Monica
CC BY-SA 4.0
2024-06-13T23:22:32.667Z
@wepajakeg Your absolute graph shows nicely that the radiation is "almost zero" already at around 13,000 feet and probably "small enough" close to 20,000 feet which is more than a quarter of the strongly absorbing atmosphere.
Peter - Reinstate Monica
CC BY-SA 4.0
2024-06-14T01:45:41.533Z
@Peter - Reinstate Monica Let's round at 10k feet. Subtract the average continental altitude 3k. We are around 5%-10% of the height of the atmosphere that affects cosmic rays, and there is an unknown variability on the data along 4 billion years of Earth's history. (also, no data at Equator).
wepajakeg
CC BY-SA 4.0
2024-06-14T03:16:05.543Z
@WaterMolecule The most earth like planets in the Solar System are Mars and Venus. Mars has orders of magnitude less atmosphere, and Venus has orders of magnitude more atmosphere. Within that immense range of variation, 4 orders of magnitude, Earth has just enough atmosphere to stop cosmic rays.
wepajakeg
CC BY-SA 4.0
2024-06-14T08:35:29.083Z
The Earth's atmosphere does not stop all cosmic rays. Cosmic rays were detected at ground level at the beginning of the 20th C. Cosmic rays can even be detected underwater -- in fact, Domenico Pacini [detected cosmic rays underwater back in 1911](https://cerncourier.com/a/domenico-pacini-and-the-origin-of-cosmic-rays/).
Peter Erwin
CC BY-SA 4.0
2024-06-12T11:31:15.370Z
2024-06-12T11:31:15.370Z
ProfRob
<p>Why does cosmic radiation diminish entirely, reaching zero, at sea level?
<a href="https://i.sstatic.net/3GQuEPul.png" rel="noreferrer"><img src="https://i.sstatic.net/3GQuEPul.png" alt="enter image description here" /></a></p>
<p>If the atmosphere's thickness were random, it should not happen at sea level, but at a random altitude.</p>
<p>Is there a specific mechanism or interaction within the Earth's atmosphere that causes this complete nullification of cosmic radiation at sea level?</p>
<p>For example, maybe nitrogen is created by cosmic rays interacting with seawater or rocks, until the density stops it? (So, perhaps all planets with water oceans should have similar atmospheric densities).</p>

CC BY-SA 4.0
2024-06-13T12:30:19.423Z
My Geiger counter confirms a couple of times per minute that the cosmic ray flux at sea level does not go all the way down to zero.
MTA
CC BY-SA 4.0
2024-06-14T09:13:30.527Z
(speculation) I think there's a bit of Anthropic Principle at play here. Earth's atmospheric thickness depends on how much air there is, and how much gravity the Earth exerts on it to keep it close to the surface. It just so happens that, for Earth, these values are appropriate for most of cosmic radiation to _not_ reach the surface — which is one of the reasons why life could develop and, ultimately, the reason why you're here asking this question :) IOW, if Earth had less air or gravity, cosmic radiation _would_ reach the surface, and you wouldn't be asking this, because you wouldn't exist.
walen
CC BY-SA 4.0
2024-06-14T18:11:41.050Z
@MTA How do you know that that's due to cosmic rays, rather than some other source of background radiation?
Mark Morgan Lloyd
CC BY-SA 4.0
2024-06-14T20:59:49.053Z
Cosmic neutrinos are not at all stopped by the atmosphere.
R. J. Mathar
CC BY-SA 4.0
2024-06-14T21:00:14.493Z
@MarkMorganLloyd Process of elimination. There is no other known source of ground level *background* ionizing radiation that is continuous day and night, unchanging with wind or weather, independent of proximity to mineral deposits, etc. First studied in 1912 by Victor Hess and well known by discerning geeks everywhere since Dr Millikan of the famed oil drop experiment did extensive work in the field in the 1930s.
MTA
CC BY-SA 4.0
2024-06-15T06:12:14.343Z
@MTA Very true, but eliminating terrestrial sources is something that has to be done: you can't just say "there aren't any" when the user might- for example- turn out to be in an older building with radon contamination or unshielded vintage equipment.
Mark Morgan Lloyd
CC BY-SA 4.0
2024-06-15T14:50:24.327Z
@MarkMorganLloyd Yes, of course if it's one user in one place at one time, who can say what the source is. But when it's every Geiger counter in the world, everywhere, all the time, continuous and unchanging, the source is well settled.
MTA
CC BY-SA 4.0
2024-06-16T00:14:32.983Z
@walen Earth's atmosphere could easily be double what it is now, and that wouldn't stop life. Mars' atmosphere is approximately 1% of Earth's, while Venus' is approximately 100 times greater. Therefore, Earth's atmosphere could vary by about four orders of magnitude. As shown in the chart, cosmic rays radiation get's close to zero, very close to the surface. Arguing about residual radiation that is orders of magnitude lower is irrelevant to the point being discussed, and is just frivolous. The matter is if there is a cause and effect between the facts shown.
wepajakeg
<planetary-atmosphere><radiation><atmospheric-effects><cosmic-ray>
Is Earth's Atmospheric Thickness Related to Cosmic Ray Radiation?
wepajakeg
# Is Earth's Atmospheric Thickness Related to Cosmic Ray Radiation?

(Asked by: username_0 on 2024-06-12)

Why does cosmic radiation diminish entirely, reaching zero, at sea level?
[![enter image description here](https://i.sstatic.net/3GQuEPul.png)](https://i.sstatic.net/3GQuEPul.png)

If the atmosphere's thickness were random, it should not happen at sea level, but at a random altitude.

Is there a specific mechanism or interaction within the Earth's atmosphere that causes this complete nullification of cosmic radiation at sea level?

For example, maybe nitrogen is created by cosmic rays interacting with seawater or rocks, until the density stops it? (So, perhaps all planets with water oceans should have similar atmospheric densities).

**Tags:** planetary-atmosphere, radiation, atmospheric-effects, cosmic-ray
> **Comments:**
> **username_1**: My Geiger counter confirms a couple of times per minute that the cosmic ray flux at sea level does not go all the way down to zero.  
> **username_2**: (speculation) I think there's a bit of Anthropic Principle at play here. Earth's atmospheric thickness depends on how much air there is, and how much gravity the Earth exerts on it to keep it close to the surface. It just so happens that, for Earth, these values are appropriate for most of cosmic radiation to _not_ reach the surface — which is one of the reasons why life could develop and, ultimately, the reason why you're here asking this question :) IOW, if Earth had less air or gravity, cosmic radiation _would_ reach the surface, and you wouldn't be asking this, because you wouldn't exist.  
> **username_3**: @MTA How do you know that that's due to cosmic rays, rather than some other source of background radiation?  
> **username_4**: Cosmic neutrinos are not at all stopped by the atmosphere.  
> **username_1**: @MarkMorganLloyd Process of elimination. There is no other known source of ground level *background* ionizing radiation that is continuous day and night, unchanging with wind or weather, independent of proximity to mineral deposits, etc. First studied in 1912 by Victor Hess and well known by discerning geeks everywhere since Dr Millikan of the famed oil drop experiment did extensive work in the field in the 1930s.  
> **username_3**: @MTA Very true, but eliminating terrestrial sources is something that has to be done: you can't just say "there aren't any" when the user might- for example- turn out to be in an older building with radon contamination or unshielded vintage equipment.  
> **username_1**: @MarkMorganLloyd Yes, of course if it's one user in one place at one time, who can say what the source is. But when it's every Geiger counter in the world, everywhere, all the time, continuous and unchanging, the source is well settled.  
> **username_0**: @walen Earth's atmosphere could easily be double what it is now, and that wouldn't stop life. Mars' atmosphere is approximately 1% of Earth's, while Venus' is approximately 100 times greater. Therefore, Earth's atmosphere could vary by about four orders of magnitude. As shown in the chart, cosmic rays radiation get's close to zero, very close to the surface. Arguing about residual radiation that is orders of magnitude lower is irrelevant to the point being discussed, and is just frivolous. The matter is if there is a cause and effect between the facts shown.  

---

## 1 answers

### Answer by username_5 on 2024-06-12. Score: 25 | Accepted answer

It won't be (and isn't) zero. To see that, you want the plot on a logarithmic scale. Thus there isn't really a question to answer. The attenuation of cosmic rays will follow some exponential decay with airmass. Since most of the airmass is at low altitudes then that is where most of the attenuation takes place. The Earth's magnetic field is also a factor, which is why there is a latitude dependence.

Here's a similar diagram but with a logarithmic dose scale ([Hwang et al. 2010](http://koreascience.or.kr/article/JAKO201017337337120.page)).

[![Dose vs altitude](https://i.sstatic.net/yBobI60w.png)](https://i.sstatic.net/yBobI60w.png)

> **Comments:**
> **username_6**: I would imagine there's also some latitude dependence due to oblateness of the atmosphere.  
> **username_0**: I'm not convinced that 0.001 is significantly different from zero, or that "the air mass is at low altitudes is where most of the attenuation takes place", since the highest slope on the chart is around 40,000 feet  
> **username_7**: @wepajakeg A vertical slope on that figure means *little or no attentuation*, since the amount of cosmic rays isn't changing with altitude. *Strong* attenuation happens when the slope is closer to horizontal: as you go down in altitude, the number of cosmic rays you can detect goes down (a lot).  
> **username_8**: If I'm reading this correctly, the muon and photon curves (and, just barely, the electron and neutron curves) fold back on themselves at higher altitudes.  Is there an obvious reason for this, or should I make it a new question?  My own best guess is secondary radiation from proton (or unmentioned) collisions in the stratosphere.  
> **username_9**: @CristobolPolychronopolis Yes, it's secondary radiation, and yes, you should make a new question.  
> **username_0**: @Peter Erwin but the problem is why the air density reaches the necessary density close to the surface. If the amount of air in earth were random, it should most probably be reached at higher altitude, or below sea level (not reached).  
> **username_10**: @wepajakeg The graph shows that there is nothing special about sea level. What do you mean by "necessary density"? If you go to lower altitudes (assuming you could dig a big hole), the effective dose rate would keep going down exponentially.  
> **username_11**: @WaterMolecule The special thing about sea level (and a few kilometers above)  is that 98% or so of the lethal cosmic radiation has been absorbed. The logarithmic scale shows that it is never zero but the absolute scale shows clearer that it is "good enough" for us. Which is no coincidence, if only for the anthropic principle.  
> **username_11**: @wepajakeg Your absolute graph shows nicely that the radiation is "almost zero" already at around 13,000 feet and probably "small enough" close to 20,000 feet which is more than a quarter of the strongly absorbing atmosphere.  
> **username_0**: @Peter - Reinstate Monica Let's round at 10k feet. Subtract the average continental altitude 3k. We are around 5%-10% of the height of the atmosphere that affects cosmic rays, and there is an unknown variability on the data along 4 billion years of Earth's history. (also, no data at Equator).  
> **username_0**: @WaterMolecule The most earth like planets in the Solar System are Mars and Venus. Mars has orders of magnitude less atmosphere, and Venus has orders of magnitude more atmosphere. Within that immense range of variation, 4 orders of magnitude, Earth has just enough atmosphere to stop cosmic rays.  
> **username_7**: The Earth's atmosphere does not stop all cosmic rays. Cosmic rays were detected at ground level at the beginning of the 20th C. Cosmic rays can even be detected underwater -- in fact, Domenico Pacini [detected cosmic rays underwater back in 1911](https://cerncourier.com/a/domenico-pacini-and-the-origin-of-cosmic-rays/).  

---

