Who planet has an atmosphere that would crush a human?
Assuming the planet was just like Earth in every other way... First, the planet would have to be large enough to have enough gravity to sustain an atmosphere, or it would be impossible for a human to survive. As long as the planet had enough atmospheric pressure, then a human could survive, but their bones would slowly degenerate because when there is someone is not subjected to enough gravity, the bones become weaker.
Life as we know it requires both water and air. Certainly human beings cannot live without those things. So from our point of view, it is very convenient to be living on a planet that has both an atmosphere and a hydrosphere. It would be much harder to live on a planet such as Mercury, which has neither of those things.
Yes, most definitely. Jupiter is a large ball of gas (biggest planet in our solar system). The weight of all that gas surrounding you, above you, would most definitely crush you. Our next door neighbour Venus (brightest object in the sky) has an atmosphere of Carbon Dioxide. Due to the run away greenhouse effect on our sister planet, the atmosphere is very thick - lots of gas = high pressure. The atmospheric pressure on Venus…
That depends on when you consider a planet to be "really small." Mars is much smaller than Earth, but it still retains an atmosphere. Mercury, the smallest planet in the solar system, does not have an atmosphere, but it is also very close to the sun, which would tend to drive away atmospheric gasses.
It depends entirely upon the conditions of the planet. If the planet was too small for its own atmosphere or an atmosphere that was toxic to humans, some sort of airtight base would have to be established. If the planet had conditions similar to Earth, humans could potenially live there. But, there would be a great chance that lifeforms had already evolved there.
Venus has an atmosphere containing 99% Carbon dioxide, so if you didn't die of asphyxiation, the crushing force of atmospheric pressure would have an accordion-like effect on the human body, pushing it into the ground somewhat comically. Following that, the temperature of 460 degrees C would burn the remains of the body.