<p>Considering the presence of speleothems, indicating the infiltration of water along fractures (i.e. fracture permeability), and the range of daily tides in the vicinity (noted as presently about 0.8 ft, or 0.24 m), one would suspect that there is at present an exchange of air with the exterior atmosphere.  Air would be gently pulled into the cave along permeable fractures during the transition to low tide, and be similarly exhausted during the transition to high tide.  Consequently, the composition of the air in the cave would be similar to, or exactly the same as, the exterior air outside of the cave.</p>

CC BY-SA 4.0
2024-02-19T19:39:24.040Z
2024-02-19T19:39:24.040Z
Thomas Perry
<p>It's extremely likely that the cave was on dry land a few tens of thousands of years ago. Early humans would not have had any diving equipment, so 30+ meters below the waves was downright inaccessible for our early ancestors. Also it's safe to assume the cave was once part of the mainland, as boats had probably yet to be invented. That said, it is possible that early humans did have boats of some kind, like hollowed out logs.</p>

CC BY-SA 4.0
2024-05-28T06:52:43.180Z
2024-05-28T06:52:43.180Z
Costillo
<p>I recently stumbled upon images of the <a href="https://en.wikipedia.org/wiki/Cosquer_Cave" rel="nofollow noreferrer">Cosquer cave</a> in France, famous for being a recently discovered Paleolithic decorated cave.</p>
<p>The entrance to the cave now is more than 30m below the waterline and, according to Wikipedia, has presumably been underwater since the Holocene.</p>
<p>In the photo attached, we can see the diver breathing the cave air.</p>
<p>I wondered what the initial air would be when humans entered the cave if we assumed the cave was in rocky strata. The source of gas for an extended period was the seawater column.</p>
<p>Would it be correct to say that the air composition should be similar to when the cave started being underwater, or are there processes that would ensure the air in it would be identical to the one in the outside atmosphere nearby?</p>
<p>I understand there can be several ways in which gas exchange could happen.</p>
<p><a href="https://i.sstatic.net/5CVQa.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/5CVQa.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2024-02-20T22:48:27.740Z
note the cave was not occupied during the Holocene it was occupied during the late Pleistocene, when the entrance was above water. when the cave was entered by humans it was well above sea level. or are you talking about when it was entered by modern divers?
John
CC BY-SA 4.0
2024-03-25T12:15:29.310Z
@John yes, about modern divers.
Gnudiff
<geology><geochemistry><hydrology><atmospheric-chemistry>
Likely air composition in cave only accessible from underwater?
Gnudiff
# Likely air composition in cave only accessible from underwater?

(Asked by: username_0 on 2024-02-19)

I recently stumbled upon images of the [Cosquer cave](https://en.wikipedia.org/wiki/Cosquer_Cave) in France, famous for being a recently discovered Paleolithic decorated cave.

The entrance to the cave now is more than 30m below the waterline and, according to Wikipedia, has presumably been underwater since the Holocene.

In the photo attached, we can see the diver breathing the cave air.

I wondered what the initial air would be when humans entered the cave if we assumed the cave was in rocky strata. The source of gas for an extended period was the seawater column.

Would it be correct to say that the air composition should be similar to when the cave started being underwater, or are there processes that would ensure the air in it would be identical to the one in the outside atmosphere nearby?

I understand there can be several ways in which gas exchange could happen.

[![enter image description here](https://i.sstatic.net/5CVQa.png)](https://i.sstatic.net/5CVQa.png)

**Tags:** geology, geochemistry, hydrology, atmospheric-chemistry

> **Comments:**
> **username_1**: note the cave was not occupied during the Holocene it was occupied during the late Pleistocene, when the entrance was above water. when the cave was entered by humans it was well above sea level. or are you talking about when it was entered by modern divers?  
> **username_0**: @username_1 yes, about modern divers.  

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## 2 answers

### Answer by username_2 on 2024-02-19. Score: 4 | Accepted answer

Considering the presence of speleothems, indicating the infiltration of water along fractures (i.e. fracture permeability), and the range of daily tides in the vicinity (noted as presently about 0.8 ft, or 0.24 m), one would suspect that there is at present an exchange of air with the exterior atmosphere. Air would be gently pulled into the cave along permeable fractures during the transition to low tide, and be similarly exhausted during the transition to high tide. Consequently, the composition of the air in the cave would be similar to, or exactly the same as, the exterior air outside of the cave.


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### Answer by username_3 on 2024-05-28. Score: 1

It's extremely likely that the cave was on dry land a few tens of thousands of years ago. Early humans would not have had any diving equipment, so 30+ meters below the waves was downright inaccessible for our early ancestors. Also it's safe to assume the cave was once part of the mainland, as boats had probably yet to be invented. That said, it is possible that early humans did have boats of some kind, like hollowed out logs.


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