
A plunge in incoming sunlight may have triggered 'Snowball Earths' - pseudolus
https://phys.org/news/2020-07-plunge-incoming-sunlight-triggered-snowball.html
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jonnycomputer
There are many really interesting episodes in Earth's history. The one that
I'm really fascinated by lately is the so called Azolla Event, in which it is
hypothesized that Azolla aquatic ferns at the North Pole at the beginning of
the Eocene soaked up carbon from the atmosphere, to be deposited on the sea
floor, taking the earth from a hothouse (where the poles were above freezing)
to an icehouse.

[https://en.wikipedia.org/wiki/Azolla_event](https://en.wikipedia.org/wiki/Azolla_event)

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ip26
It begins to look like every large drop in atmospheric carbon is linked to
photosynthesis, in one way or another.

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thangalin
You may find the Great Oxygenation Event from my book to be of relevance (it
supports what you're saying):

[https://impacts.to/preview.html](https://impacts.to/preview.html)

If you'd rather read it as a PDF instead of images:

[https://impacts.to/downloads/lowres/impacts.pdf](https://impacts.to/downloads/lowres/impacts.pdf)

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chrisco255
Volcanoes seem like most likely culprit. Although, I wonder if there was
evidence of reduced geomagnetism which increased cosmic ray cloud nucleation
via the Svensmark Effect. See:

Winter monsoons became stronger during geomagnetic reversal
[https://www.sciencedaily.com/releases/2019/07/190703121407.h...](https://www.sciencedaily.com/releases/2019/07/190703121407.htm)

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User23
The Milankovitch cycles[1] almost certainly play a significant role. The
arrangement of the continents also has a huge effect on climate, because an
Earth with only one large ocean transfers heat much differently than one with
two major oceans. It's largely because of the positions of the continents,
including a large polar continent, that we are still in an ice age[2]. However
an event like a massive volcanic discharge could conceivably start a positive
feedback loop of cooling. Since ice has a high albedo, we could get a runaway,
well, snowball effect.

[1]
[https://en.wikipedia.org/wiki/Milankovitch_cycles](https://en.wikipedia.org/wiki/Milankovitch_cycles)
[2]
[https://en.wikipedia.org/wiki/Quaternary](https://en.wikipedia.org/wiki/Quaternary)

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wwarner
This is a strange result -- it's saying that an ice age could be caused by a
change in sunlight. With made up numbers, it's saying that a change from
100W/m2 to 60W/m2 could cause an ice age, even though a stable regime at
60W/m2 would not create an ice age. Even if it just claims that a change in
temp speeds the onset of an ice age that's surprising to me.

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brandmeyer
The positive gain from albedo feedback has been well-known for quite some
time. Its part of why the Arctic is heating up so much faster than the rest of
the world right now.

The negative gain from weathering and volcanism is also quite well-known.

The authors of this paper put 2 and 2 together and showed that you only need a
brief period of reduced insolation to trigger a snowball earth, and that once
insolation returns to normal it can stay in the snowball state for much
longer.

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compscistd
Weird question, how large would an alien spaceship have to be to position
itself between the sun and the earth and cause us major problems? Distance
would also play a factor as would the degree of “major problem” (varying
effects on plant life/temperature). The equivalent of finding a parked car in
front of your driveway, on a cosmic scale.

Would be fun to learn the mathematics, physics, and macrobiology to solve
this!

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alquemist
An object capable to completely shade Earth must be larger than Earth itself.
The Moon can only shade a small fraction of Earth at a time, see eclipse path
maps, for example
[https://www.timeanddate.com/eclipse/map/2024-april-8](https://www.timeanddate.com/eclipse/map/2024-april-8).

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riverdweller
This is plainly untrue.

Hold a finger up in front of a torch, and look at the size of the shadow cast.
Move the finger closer to the torch, and watch the shadow area increase.

A shadow is always larger than the light-facing area of the object blocking
the light. This is true even of your own shadow in sunlight, even though your
distance from the light source means the change is so tiny you don't even
notice it.

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ben_w
A finger is comparable size to a torch. Not much light goes around a finger
despite the non-zero size of the light source making the rays both non-
parallel and originating from different places.

Sol has a diameter of ~100 times the Earth. A shade near Earth would have to
be similar size to Earth to block most of the light, and likewise similar size
to Sol if it was near Sol.

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riverdweller
That's a good point. I made the mistake of treating the sun as a point light
source, which of course it is not!
[https://www.timeanddate.com/eclipse/shadows.html](https://www.timeanddate.com/eclipse/shadows.html)
explains the difference clearly.

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foxhop
My guess is the actual sun has periods of less activity / heat.

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ben_w
How would that even be possible on these scales?

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d_silin
The article mentions in the end that the opposite effect of rapid warming-up
might be possible, tripped by a similar rapid spike in one of the global
climate variables.

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jjclarkson
A large asteroid is the obvious possibility to create such an event

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goatlover
I doubt the dust from a large impact would stay in the atmosphere long enough
to trigger a snowball earth. It didn't happen with the Chicxulub impact/non-
avian dinosaur extinction.

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leptoniscool
All life that survived snowball Earth has genes that improves health in cold
temperatures, and this has been documented in humans as well.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4486781/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4486781/)

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vkou
The article you cited makes no claims about 'all life having genes that
improve its health in cold temperatures'.

The leap between its claim, and yours, is massive, and would require
incredibly extraordinary evidence.

