In Latin American history, the Pre-Columbian Era refers to the time .

Had a democratic form of government

No, because you are more likely to see volcanic mountains where magma is rising along the mid-ocean ridge spreading to the center.

Bcold,less-dense air falls

It's probably because the earth is actually tilted and is not straight when orbiting the sun. that's why when it's winter here, it's summer in the southern hemisphere. in the wintertime in the northern hemisphere, it's colder here because it's tilted away from the sun and the southern hemisphere is tilted closer to the sun (i believe this is the case anyways)