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I am building a setting that is essentially steampunk,being exact it would be pneumatic punk. What electronics and electronic equivalent exists, are primitive and extremely expensive. Thus the majo...
I'm going to talk about Earth below, but since you say "an Earth-like planet", consider that just an space-saving measure. Take an Earth-like planet, about the same size, composition and gravit...
The first thing that comes to mind is an incredibly large volcanic eruption. And I mean a huge eruption. Something never before seen on Earth. One of the largest (if not the largest) eruptions we k...
I think we've established that this monstrous object is going to have to be pretty darn big. You suggested that it could be 500 kilometers in diameter; let's do the calculations to figure out just ...
Broadly speaking you need three things: (1) something that makes it infeasible to keep living on land (most people won't move unless pushed), (2) the inability to evacuate from the planet, and (3) ...
Actually, some of the challenges you describe might not be too hard to overcome. Maybe you've thought of the same things I have. Metals I'll tackle smelting first. The key issue you described is ...
Under the circumstances you describe, my immediate reaction is that it would not be possible. The issue here is that the cluster would be fairly unstable. The black holes would all be mutually attr...
A planet could definitely have multiple gas layers. As was discussed here, gravity affects different gases differently, based on their mass. In other words, there would be more force between the Ea...
Let's say you have a planet pretty similar to Earth. It resembles Earth at around the time life is thought to have begun - except that it's a bit less hostile to life. The atmosphere is mainly carb...
Their main problem would probably be to find food. Plants don't grow underground/without sunlight. Of course, if they have sufficient supply of canned food to survive until the surface is habitable...
My choices: Ganymede and Callisto (and maybe Titan) This is perhaps a bit of a buzzkill, but I honestly would not recommend colonizing much in the solar system besides the Moon and Mars. Here's wh...
From the viewpoint of evolutionary dynamics, the reason why very few species are both autotrophic (photosynthesizing) and heterotrophic (hunting / foraging on other living organism) at the same tim...
This is really sort of cheating, but it could actually work, so here it goes. As professorfish says, It is theoretically possible, but I don't know how you could rip off the atmosphere and man...
One possibility that has not yet been mentioned (actually inspired from githubphagocyte's comment on how the evolution of plants began in the first place): It could be that the animal doesn't do ph...
As Neil pointed out, there is no absolute frame of reference, so I'll pretend that the frame of reference is relative to something - in some scenarios, the Sun; in others, the Earth, and in others,...
I'm actually going to answer the question from the opposite viewpoint of TimB, if only because there are some loopholes to a lack of fire. They primarily apply to deep-sea civilizations, but still,...
As others noted, there's no real physical effect that does this. However let's look at how a fictional effect might work. Water can be supercooled to quite low temperatures, that means, there does...
Hit it with a rock. A big rock. Something like Ceres might do, if you could somehow get it into an orbit that hits the moon with sufficient relative velocity. Alas, moving Ceres significantly fr...
TL;DR To make a long story short, the planet will lose its atmosphere and some of its crust, but most of it will remain intact, even in the worst-case scenario. That should be the major effect you...
This is only a partial answer (it only addresses land animals), but I don't know if anyone else is going to mention it, so I might as well. Land animals rely on their bodies to support their weigh...
I'll take a completely different approach from what everyone else is saying, because everyone (okay, sans ivy_lynx) seems to be assuming that there are asteroids in planetary rings. This is not tru...
I think an interesting option could also be that dragons can switch between cold-blooded and warm-blooded metabolism. For example, they could be warm-blooded when young (providing them the needed e...
I'm actually going to consider how such a year would affect animals, because I have a feeling nobody else is planning on addressing it. This should be short and to the point, unlike some of my othe...
I'll narrow down your list by talking about all the stars you shouldn't use. You'll find it gives you a pretty narrow range. Let's start with the exciting ones: neutron stars. These are, technical...
Apart from the problems of formation and the problems of mechanical stability already mentioned by others, there's also the problem that gravitation cannot preserve that situation. If the sphere w...
