<p>The optical extinction through a typical Bok globule is 20-30 magnitudes (e.g. <a href="https://iopscience.iop.org/article/10.1088/0004-637X/703/2/1444" rel="noreferrer">Racca et al. 2009</a>). If the Bok globule is say a light year thick, that amounts to less than a milli-magnitude of extinction per astronomical unit.</p>
<p>i.e. the dust density in a Bok globule is nowhere near high enough, by many orders of magnitude, to cause any significant obscuration of the Sun.</p>

CC BY-SA 4.0
2024-09-17T20:42:10.073Z
2024-09-17T20:42:10.073Z
ProfRob
<p>Bok globules are unlikely as explanations for <a href="https://Grading%20Extropian%20Predictions" rel="noreferrer">Snowball Earth episodes</a>, mainly because of their duration. The Huronian lasted 300 my, the Sturtian 57 my, and the Marinoan 22.2 my. This is much longer than a 0.2 lightyear globule is likely to remain near the solar system.</p>
<p>Furthermore, as commenters have pointed out, the material density needed to reduce sunlight significantly would also imply a lot of material deposited, which has not been observed. Finally, if the globule was dense enough to intercept sunlight strongly, the light pressure from the sun would also blow it away strongly.</p>
<p>There is some debate about what triggers snowball episode, and maybe an interstellar event might be involved there. But the maintenance of the episode is fairly well understood as moving to a high albedo equilibrium due to the ice rather than a long reduction of insolation.</p>

CC BY-SA 4.0
2024-09-17T18:17:58.397Z
Yes it's a very strong rhetoric against the theory. I disagree that the sun would send all the material away, i.e. the solar system would transition through the bok cloud at i.e. 32 km/s and the dust would be blown away at 1 to 10 km/s... It's not possible to have a Bok or a meolecular cloud which envolps the world for more than 50k years perhaps 1 Mya for a giant cloud of 100 ly depth, and that would mean an accumulation of 5-10 meters of foreign materials... I'm still in favor of imagining that there can some layers evidencing gigakilos of bok material in billion year old rocks.
bandybabboon
CC BY-SA 4.0
2024-09-17T19:25:50.647Z
Just a heads up, your link is broken; looks like you pasted the wrong thing.
Idran
CC BY-SA 4.0
2024-09-17T20:01:17.960Z
"rhetoric" implies that it's just persuasive writing rather than strong scientific evidence
Darth Pseudonym
CC BY-SA 4.0
2024-09-18T08:20:41.957Z
Ok. Rhetoric is bad wording. better words are discourse and reasoning, even rational inquiry.
bandybabboon
CC BY-SA 4.0
2024-09-17T09:55:11.263Z
2024-09-17T09:55:11.263Z
Anders Sandberg
<p>Bok clouds are tenebrous regions of .1 to 2 light years diameter and 2-50 solar masses.</p>
<p>Gliese 710 will pass at 0.06 ly of us in 1.28 million years, so isn't it very probable that we have been through some dense space dust and bok globules in the previous 1 billion years, and the sea just froze to a km of ice?</p>
<p>Perhaps <a href="https://en.wikipedia.org/wiki/Snowball_Earth" rel="noreferrer">Snowball Earth</a> was due to bok globules?</p>
<p>Is it reasonable to think so?</p>

CC BY-SA 4.0
2024-09-17T02:31:19.127Z
What is "snowballing"?
uhoh
CC BY-SA 4.0
2024-09-17T02:33:58.887Z
@uhoh - https://en.m.wikipedia.org/wiki/Snowball_Earth
Jon Custer
CC BY-SA 4.0
2024-09-17T03:11:33.100Z
Are you proposing that the Solar System may have passed through a dust cloud dense enough to dramatically affect the solar energy reaching the Earth? Wouldn't that leave a significant "footprint" of dust in the geological record?
PM 2Ring
CC BY-SA 4.0
2024-09-17T05:22:24.647Z
Without trying to work out if it possible, this seems to be an explanation in search of a problem.  There's no difficulty in understanding why Earth might go into an extreme ice age.  We've had significant glaciation in the last 100.000 years,  so we know there is that kind of variation in climate, Throw in a major dip in CO2 from disrupted geochemical cycle and Algal removal of CO2, and dim early sun. Indeed, the only surprise might be that "snowball earth" wasn't more common.  There's no need to propose space dust etc
James K
CC BY-SA 4.0
2024-09-17T05:44:17.593Z
@James_K, We are passing at 0.5 light years of alpha centauri in only 65,000 years, perhaps there can have been dense dust clouds in the previous million years. A global algal bloom needs regular warm conditions, that coal evidence is known from carboniferous. Has a significant carbon, coal, oil source ever been found pre-carbonifeeous? Space dust is very common, is it likely that we can travel right around the galaxy twice and through the plane of the disk 20 times and not have significant space cloud episodes.
bandybabboon
CC BY-SA 4.0
2024-09-17T06:14:12.507Z
@PM_2Ring if there was 750 billion kilos of dust intercepting 50% of sun rays, then we'd pick up perhaps 2250 billion kilos every year, so 4.5g on every m2 of the planet, a 45 kilo rock equivalent over 45,000 years. Including iron, water, metals, silicon, how can we detect  a 4.5cm global sedimentary layer from 500million to 1 billion years ago? It would be transported by the glacial flowd and ice?
bandybabboon
CC BY-SA 4.0
2024-09-17T07:50:58.307Z
@bandybabboon easily by chemical composition. The asteroid which exterminated the dinosaurs was maybe similar mass, and is also detectable in sediments.
planetmaker
CC BY-SA 4.0
2024-09-17T10:59:57.353Z
Yes, irridium bonds with iron and is rare on the planet surface, however irridium timing is scarecly studied prior to 500 Mya, the geological record is incomplete, there's just 1 irridium event discovered older than 450 Mya? here is a list: Cretaceous–Paleogene (K-Pg) - 66 MA; Eocene-Oligocene Limit - 34 MA; Paleocene-Eocene Thermal Maximum (PETM) - 56 MA; Sudbury Impact - 1,850 MA; Popigai Crater - 35 MA; Chesapeake Bay Crater - 35 MA; Permian-Triassic Boundary - 252 MA; Frasnian-Famennian Boundary - 372 MA; Triassic-Jurassic Boundary- 201 MA; Ordovician-Silurian Event - 445 MA.
bandybabboon
CC BY-SA 4.0
2024-09-17T11:28:45.953Z
@planetmaker because we have found 5 iridium markers since 100 MA, the complete list of events since 1 billion years ago is at least 400, however, because of the lack of fossils we'd have to conduct a zircon chronology - iridium study of every 10,000 years group of rocks ever found to discover new iridium periods.
bandybabboon
CC BY-SA 4.0
2024-09-17T12:01:18.800Z
Fossils go back 4 billion years, thus are not lacking
planetmaker
CC BY-SA 4.0
2024-09-17T14:29:02.807Z
@JonCuster I've put that in the question so others may also benefit. I did a lot of snowballing in the winter when I was a kid (from behind the walls of my snow fort), but I knew it had to  e something different.
uhoh
CC BY-SA 4.0
2024-09-18T06:15:30.787Z
Closely related https://astronomy.stackexchange.com/questions/27862/how-dark-would-the-sun-become-if-we-traversed-a-bok-globule
ProfRob
CC BY-SA 4.0
2024-09-18T06:43:13.247Z
Methinks somebody's been reading a certain eminent astronomer's science fiction.
Mark Morgan Lloyd
CC BY-SA 4.0
2024-09-18T07:39:29.400Z
@planetmaker, 26 fossils for 1.5 billion years of the archean is not very complete for a fossil record, 0.018 fossils for every million years. Here is the fossil record, you can see for yourself: https://paleobiodb.org/classic/displayTimescale?interval=Proterozoic there is about 0.3 fossils for every million  years of the proterozoic... 3000 fossils for every million years in the cretacious, 5000 per Mya of the paleogene. The other SE related question about bok density negates OP question.
bandybabboon
CC BY-SA 4.0
2024-09-19T08:30:20.927Z
@bandybabboon I don't think Alpha Centauri will be that close... from the graph I see it doesn't appear closer than ~3ly.
Michael
CC BY-SA 4.0
2024-09-20T16:00:25.377Z
Yes you are right, 3.2ly ... Another probability figure is that 0.1% of of the galaxy is a cloud, so if we are travelling for 1 billion years, about 1 million years would average through molecular clouds, even though, as noted, they are too sparse to have much effect.
bandybabboon
<galaxy><earth>
Was the total glaciation of the world, a.k.a. snowball earth, due to Bok space clouds?
bandybabboon
# Was the total glaciation of the world, a.k.a. snowball earth, due to Bok space clouds?

(Asked by: username_0 on 2024-09-17)

Bok clouds are tenebrous regions of .1 to 2 light years diameter and 2-50 solar masses.

Gliese 710 will pass at 0.06 ly of us in 1.28 million years, so isn't it very probable that we have been through some dense space dust and bok globules in the previous 1 billion years, and the sea just froze to a km of ice?

Perhaps [Snowball Earth](https://en.wikipedia.org/wiki/Snowball_Earth) was due to bok globules?

Is it reasonable to think so?

**Tags:** galaxy, earth
> **Comments:**
> **username_1**: What is "snowballing"?  
> **username_2**: @uhoh - https://en.m.wikipedia.org/wiki/Snowball_Earth  
> **username_3**: Are you proposing that the Solar System may have passed through a dust cloud dense enough to dramatically affect the solar energy reaching the Earth? Wouldn't that leave a significant "footprint" of dust in the geological record?  
> **username_4**: Without trying to work out if it possible, this seems to be an explanation in search of a problem.  There's no difficulty in understanding why Earth might go into an extreme ice age.  We've had significant glaciation in the last 100.000 years,  so we know there is that kind of variation in climate, Throw in a major dip in CO2 from disrupted geochemical cycle and Algal removal of CO2, and dim early sun. Indeed, the only surprise might be that "snowball earth" wasn't more common.  There's no need to propose space dust etc  
> **username_0**: @James_K, We are passing at 0.5 light years of alpha centauri in only 65,000 years, perhaps there can have been dense dust clouds in the previous million years. A global algal bloom needs regular warm conditions, that coal evidence is known from carboniferous. Has a significant carbon, coal, oil source ever been found pre-carbonifeeous? Space dust is very common, is it likely that we can travel right around the galaxy twice and through the plane of the disk 20 times and not have significant space cloud episodes.  
> **username_0**: @PM_2Ring if there was 750 billion kilos of dust intercepting 50% of sun rays, then we'd pick up perhaps 2250 billion kilos every year, so 4.5g on every m2 of the planet, a 45 kilo rock equivalent over 45,000 years. Including iron, water, metals, silicon, how can we detect  a 4.5cm global sedimentary layer from 500million to 1 billion years ago? It would be transported by the glacial flowd and ice?  
> **username_5**: @bandybabboon easily by chemical composition. The asteroid which exterminated the dinosaurs was maybe similar mass, and is also detectable in sediments.  
> **username_0**: Yes, irridium bonds with iron and is rare on the planet surface, however irridium timing is scarecly studied prior to 500 Mya, the geological record is incomplete, there's just 1 irridium event discovered older than 450 Mya? here is a list: Cretaceous–Paleogene (K-Pg) - 66 MA; Eocene-Oligocene Limit - 34 MA; Paleocene-Eocene Thermal Maximum (PETM) - 56 MA; Sudbury Impact - 1,850 MA; Popigai Crater - 35 MA; Chesapeake Bay Crater - 35 MA; Permian-Triassic Boundary - 252 MA; Frasnian-Famennian Boundary - 372 MA; Triassic-Jurassic Boundary- 201 MA; Ordovician-Silurian Event - 445 MA.  
> **username_0**: @planetmaker because we have found 5 iridium markers since 100 MA, the complete list of events since 1 billion years ago is at least 400, however, because of the lack of fossils we'd have to conduct a zircon chronology - iridium study of every 10,000 years group of rocks ever found to discover new iridium periods.  
> **username_5**: Fossils go back 4 billion years, thus are not lacking  
> **username_1**: @JonCuster I've put that in the question so others may also benefit. I did a lot of snowballing in the winter when I was a kid (from behind the walls of my snow fort), but I knew it had to  e something different.  
> **username_6**: Closely related https://astronomy.stackexchange.com/questions/27862/how-dark-would-the-sun-become-if-we-traversed-a-bok-globule  
> **username_7**: Methinks somebody's been reading a certain eminent astronomer's science fiction.  
> **username_0**: @planetmaker, 26 fossils for 1.5 billion years of the archean is not very complete for a fossil record, 0.018 fossils for every million years. Here is the fossil record, you can see for yourself: https://paleobiodb.org/classic/displayTimescale?interval=Proterozoic there is about 0.3 fossils for every million  years of the proterozoic... 3000 fossils for every million years in the cretacious, 5000 per Mya of the paleogene. The other SE related question about bok density negates OP question.  
> **username_8**: @bandybabboon I don't think Alpha Centauri will be that close... from the graph I see it doesn't appear closer than ~3ly.  
> **username_0**: Yes you are right, 3.2ly ... Another probability figure is that 0.1% of of the galaxy is a cloud, so if we are travelling for 1 billion years, about 1 million years would average through molecular clouds, even though, as noted, they are too sparse to have much effect.  

---

## 2 answers

### Answer by username_9 on 2024-09-17. Score: 25 | Accepted answer

Bok globules are unlikely as explanations for [Snowball Earth episodes](https://Grading%20Extropian%20Predictions), mainly because of their duration. The Huronian lasted 300 my, the Sturtian 57 my, and the Marinoan 22.2 my. This is much longer than a 0.2 lightyear globule is likely to remain near the solar system.

Furthermore, as commenters have pointed out, the material density needed to reduce sunlight significantly would also imply a lot of material deposited, which has not been observed. Finally, if the globule was dense enough to intercept sunlight strongly, the light pressure from the sun would also blow it away strongly.

There is some debate about what triggers snowball episode, and maybe an interstellar event might be involved there. But the maintenance of the episode is fairly well understood as moving to a high albedo equilibrium due to the ice rather than a long reduction of insolation.

> **Comments:**
> **username_0**: Yes it's a very strong rhetoric against the theory. I disagree that the sun would send all the material away, i.e. the solar system would transition through the bok cloud at i.e. 32 km/s and the dust would be blown away at 1 to 10 km/s... It's not possible to have a Bok or a meolecular cloud which envolps the world for more than 50k years perhaps 1 Mya for a giant cloud of 100 ly depth, and that would mean an accumulation of 5-10 meters of foreign materials... I'm still in favor of imagining that there can some layers evidencing gigakilos of bok material in billion year old rocks.  
> **username_10**: Just a heads up, your link is broken; looks like you pasted the wrong thing.  
> **username_11**: "rhetoric" implies that it's just persuasive writing rather than strong scientific evidence  
> **username_0**: Ok. Rhetoric is bad wording. better words are discourse and reasoning, even rational inquiry.  

---

### Answer by username_6 on 2024-09-17. Score: 15

The optical extinction through a typical Bok globule is 20-30 magnitudes (e.g. [Racca et al. 2009](https://iopscience.iop.org/article/10.1088/0004-637X/703/2/1444)). If the Bok globule is say a light year thick, that amounts to less than a milli-magnitude of extinction per astronomical unit.

i.e. the dust density in a Bok globule is nowhere near high enough, by many orders of magnitude, to cause any significant obscuration of the Sun.


---

