How long could life survive without sunlight?

Suppose some malevolent alien race were to construct an enormous opaque screen which blocked any direct sunlight (of any frequency) from reaching the earth. Assume that the screen revolves with the earth around the sun, so that the earth never moves out of its shadow, and that, other than blocking sunlight, the screen has no other effect on the earth (e.g., no gravitational or magnetic forces). Under these conditions, how long would the earth remain habitable? Hours? Days? Weeks? How long before our atmosphere freezes? What if we had some warning and could build whatever shelters present technology allows? How long could we extend our survival using geothermal or nuclear energy (or anything else)?

Do you mean “life” in general, or “human life?”

Certain chemosynthetic bacteria do not rely on sunlight at all, and provide the basis for food chains at geothermal vents at mid-ocean ridges. These deep sea communities would continue merrily on their way until all volcanic activity at oceanic plates halts, probably in a few billion years. There are other chemosynthetic bacteria living deep underground that would also survive indefinitely. And recent studies indicate that life survived several periods whan the Earth was completely frozen over long before the Cambrian.

As for human survival, I recall a memorable science fiction story called “A Pail of Air” that described quite palusibly how some humans managed to survive, using very low technology (such as thawing buckets of frozen air by the faire), when the Earth was hurled into interstellar space by a passing rogue planet or something.

With current technology, groups of humans could build greenhouses powered by geothermal or fossil fuels, two heat sources not dependent upon the sun. We have sunlamps, that is, lamps that produce all radiations the sun gives us. We can synthesize vitamin D, so the inhabitants of regions served by greenhouses and their technology would not die of rickets. Of course, most of the surface life would die off, just like after that huge meteor crashed near the Yucatan ~65 million years ago. So it would be a relatively minor thing to construct those greenhouses and give at least a few hundred humans and some food species (rice, some grains, cattle and sheep, fish, etc.) hope for life.

None of that really gives much of an indication as to how humans would handle a sunless planet psychologically. Certain people cannot live in places like Alaska, for example, because they suffer from SAD (Seasonal Affective Disorder), a type of bipolar disorder affected by how much sunlight they receive. During dark periods (winter) they get depressive and possibly suicidal. During light periods (summer) they get manic and possibly self-destructive through their excesses. Such people respond well to sunlamp treatment, however, and could be effectively treated through alternating periods of sunlamp light and darkness simulating night and day on Earth.

And, even if that did not happen and no greenhouses were built, there are some simple species that would live on regardless, as stated above.

I am particularly curious about what would be a realistic description of how things would proceed from the moments immediately following the sun “going out”. How quickly would the surface cool to the point that a human could not survive outside unprotected (besides thick clothing)? Suppose you were on the night side of the planet when it happened. Would you notice any effects before the point where night didn’t end when it was supposed to?

not sure the greenhouse method would work as we can’t even get the biosphere project to work w/o outside resources.

We are at the point where we can realistically think about colonizing Mars and other moons around the solar system. When these colonies become self sustaining then we can probally live here on Earth w/o the Sun - then again why not just move to mars?

I think we could survive some years using fuels but since we don’t fully understand the complexity of the food chain, Im sure we’ll miss a few links and kill us off.

I disagree, k2dave. We have been cultivating and transplanting certain plants for thousands of years without ruining our ecosystem. For example, the potato, native to the New World, became such an important crop in Ireland the potato famine there caused huge starvations and a mass exodus to the New World. If potatos can live in Ireland, a few thousand miles away from their former eastermost extent, I think we can manage most of our food crops and animals even in a greatly reduced ecosystem.

BTW, the Biodome example is insightful, but not entirely relevant. A greenhouse would be more like an isolated village (as in Dark Ages Europe or prehistoric America) than a closed ‘bubble’. Granted, there would be little to no influxes of resources from the outside, but there would be some travel. And, given enough time, we could build some truly massive greenhouses. Much larger than any Biodome, more like a very well-prepared and technologically advanced small town. And if we were given warning (the flame under our butts that convinces us to get off our asses in the first place), we would decide damn quick how to solve the associated problems with the greenhouse plan.

As a final note, leaving Earth for another planet in our solar system might not be the best of plans if the sun is completely blocked (by a Dyson sphere, perhaps). If the shield is aimed against Earth (pretty wasteful move by the aliens) we might have a chance, however.

Why isn’t the answer the same as that given whenever the subject of nuclear winter comes up? Putting aside the deaths occurring from the bombs & drifting radiation, isn’t it generally agreed that the blocking out of sunlight will result in a massive die-off of vegetation? Where does our food come from after that?

I suppose the first to go would be the vegans :smiley:

From Nuclear Winter and Other Scenarios page:
What would happen in the United States and other nations if there was a distant nuclear war or nuclear winter was triggered deliberately? A preliminary analysis of USDA data indicates that stocks of food in pantries and supermarkets could feed U.S. residents for about 30 days, and stocks in warehouses another 60-90 days. After that, they would have to live on feed stocks, which might last a year with tight rationing. Such feed stocks are not well distributed, and converting them to human consumption would present processing problems. Other nations would be in much worse shape. FAO estimates world food reserves at about 33 days now.

I can’t believe that nobody’s mentioned the breathable atmosphere problems. Plants use light from the sun in photosynthesis which is the process of turning carbon-dioxide into oxygen. Take away the sun and plants will start dying off pretty quickly. Humans will continue to pump carbon dioxide into the atmosphere via respiration and other means and there will be no plants to convert the CO2. No oxygen = a pretty difficult situation for us.

I suppose we could try and construct enclosed biospheres and use artificial light to grow plants, but even biospheres which use sunlight havn’t been successfully operated. If they did work, life outside of them would be very difficult if not impossible, billions would surely die. I’d take a guess - and this is a complete guess - at a couple of months. Those lucky enough to be in biospheres would still need to power their lighting and other things, and they’d need huge amounts of lighting power to give enough energy to the masses of vegetation required to keep the occupants alive. I couldn’t see it working, but you never know.

Enclosed bunkers with carbon dioxide converters might stand a chance, but where would food come from. Food comes from either plants or animals. Animals need plants to survive and oxygen, so it’d have to be plants. A combination of a biosphere with technical equipment for converting carbon dioxide to oxygen would I reckon do the job. The vegetation could be the food that the humans require. Perhaps a dam or windmill near the biosphere could provide energy/electricity, but even if this did work, only a handfull of people would be lucky enough to have a go at survival.

Ben hit upon some points to reinforce my assumption. Windmills won’t work w/o a gas atmosphere and hydroelectric needs liquid water (or other liquid).
Water will freeze and I’m pretty sure that the air will condense out. The only power left will be nuclear and geothermal - both plentiful enough to sustain people for many years.

Manufacturing O2:
I know CO2 can easily be converted to CO + O ( 2CO2 + energy -> 2CO + O2 ) as this is a possible fuel sorce for future Mars probes. As for getting the CO bond to break, I don’t know if it is easily done. This would provide O2 for the ‘biodome/greenhouse’ and the CO would be pumped outside - further rendering the planet uninhabbital

As for transplanting plants and animals from one part of the globe to another - yes we can, and yes sometimes it’s good. But there are many examples of transplants both unintentional and intentional that failed and left the situation much worse then before. I really don’t think we got more then a basic understanding of the food chain.

When we manage to live other places in the solar system:
If the sun were completely blocked to all planets, we’d be royally F#$%*d. IMHO our best chance (if we have the technology) would leave for other nearby stars in generation ships (or hopefully ones equipped with FTL drives :wink: ) - assuming we can’t blow up the shield.

Derleth correct me if i’m wrong but you make it seem like we would life in unenclosed city’s (or futal states). I don’t see it due to lack of O2 and possible lack of atmosphere. It might be a colony of air tight buildings with connector tubes but that just adds up to a bunch of little biospheres connected.

Also a shield against Earth might not be such a wasteful idea. It would cause us a great deal of trouble and allow them (the alain race who built and installed the shield) to build an invasion fleet on any nearby planet they choose w/ the benefit of the sun. The alians then could claim the lifeless, earth and could remove the shield. Presto a planet capable of life, right smack in the goldielock zone and nobody living there.

Well, yeah. For one thing, the moon would sudden;y appear to “go out”. Most people would notice sonething like that! :slight_smile: Another is that it would get a LOT darker. Even on the dark side of the planet, you are still able to percieve a good ammount of light from the sun. I guess a lot of astronomers would be extremely happy for a few days until the riots set in.

How is this so? Presuming that is not just before dawn or just after dusk, what sunlight do you see other than what is reflected back at you from other celestial bodies?

I think it’s inevitable that a lot of people would die, but a few might be able to survive thus:

Presumably the earth will be covered with ice. Huge igloo-like “greenhouses” could be tunnelled out at the ice-earth boundary. This would have to be done in places where the ice is relatively stable and thick enough to trap essential gasses. A system of vents would maintain a relatively constant atmosphere. Energy would come from fossil fuels (in the short run, at least) and geothermal sources.

Breathable oxygen is a toughie. Probably we could geneticaly engineer “plants” that can survive without sunlight (as someone already pointed out, life has been discovered that it is not dependent on sunlight). These would be a source of food and oxygen.


I think most of those microrganisims do not produce oxygen either. But if we can produce light and heat, we can get plants to grow which will contribute some O2. But if you eat the plants or burn it as fuel or let it rot on the floor it will consume all the O2 it has created in it’s lifetime.

*Originally posted by Tyrrell McAllister *

The simplest reason is because the earth is smaller than the sun. A great percentage of the sun’s visible light goes right by the earth. Even if it’s not shining on the surface directly, you can still percieve it. This is one of the reasons people can still see at night. I’ve had this demonstrated several times on spelunking trips. Being deep underground and having the lights switched off gives you a good example of the “no sunlight” concept. You might say that the stars would give you some light. This is true to some extent, but even in their multitudes, the total light they produce would not be enough to allow you to see as well as if the sun were “still on” at the opposite side of the planet.

Sure, there’s plenty of light zooming on past the Earth, but that doesn’t matter much: You can’t see light unless it enters your eyeball, and light that misses the Earth on the first time past isn’t likely to do that, unless it bounces off the Moon or some other solar system body. You can see on a moonless night because there’s still light from the stars, from the planets, from cities withing a few hundred miles or so, and assorted other light sources.

Reminds me of a fairly recent novel by Vernor Vinge called “A Deepness in the Sky” (sequel to “A Fire Upon the Deep”–great series, read them if you have a chance), which is about a planet orbiting a star with a wildly variant radiation cycle. In the “dead end” of the cycle, the planet gets so cold the atmosphere precipitates out and the inhabitants go into hibernation. I can’t even begin to list all the cool parts of the novel (picture a Jules Verne style trek across the frozen airless surface of the planet in the dead of winter using 1910ish technology in order to sabotage an enemy base among other things). Great stuff.

Yeah, that’s about it. And on further thought, you’re right, the greenhouses would have to be pretty airtight. Thanks for pointing that out.

On the subject of just shielding the Earth: Well, if they can make and position a shield big enough to only affect Earth, they would probably also be able to make Mars habitable. Making Mars liveable seems so much easier than making the sunshield, and they would have us, a sentient race, to trade with (or just gawk at from afar). Anyway, this is tangental to the question.

According to Zero Hour (and the Professor), 5 days till Earth is solid.


Y’know, I discovered this thread for no other reason than that I’m currently reading “Journey to the Center of the Earth,” and curiosity prompted me to do an SDMB search on “Jules Verne.” Try it yourselves; you’d be surprised at the range of topics it brings up.

The solar shield idea has been proposed for a benevolent purpose, as the first step in terraforming Venus.

Venus, as we all know, is beastly hot, so the first priority is to cool it down. A surpassingly thin Mylar disk with a diameter equal to that of Venus could be positioned at a LaGrange point between Venus and the Sun. I don’t know how long it would take to make the surface temperature tolerable, but ISTR Kim Stanley Robinson suggesting (in Blue Mars that average temps would fall by 10 Kelvins per Earth year.

Obviously the Earth, being cooler to begin with, and with a much thinner atmosphere, would cool faster.


FAO Schwartz?

I have thought about this as a way of lowering the earths tempature. I think it is very simple in theory. There is a spot directly between the earth and the sun that is a (for lack of a better term) gravity neutral spot - where the 2 gravities cancle each other out effectivly. That’s where the ‘solar shade’ must go.

Using thin ultra light and reflective material it can deployed at this point. The shade would be round (like a CD) and would spin (like a cd). THe spin would hold the shade open so no structure is needed. Simular design is proposed for solar sails. The force of sunligh can be overcome by placing it a little closer to the sun.

Such a shield appears vunerable to lets say a thermonuclear device - but w/ alien tech. it could be stronger, self repairing and capable of defending itself.