The earth is an regular surface in average with a great number of small irregularities (small with respect to the global earth surface).
The geometrical center of earth is obtained by approximating the earth surface with the best fitting rotational ellipsoid, with a circular section corresponding to the equator and a minor axis joining the geographical poles.
The so called "sea level" is defined as the average distance from the geometrical center of earth of all the points on the sea surface.
The altitude of a single earth point is the difference between the distance from the earth center of that point and the conventional sea level.
water
Altitude adjustments are made for baked goods because of the effects of altitude on how dough and batter rises in baking. There are no altitude adjustments needed for cooking meats.
Air pressure decreases as altitude increases.
they are made of stuff
Cruising altitude is an economical height for an aircraft to fly. It is also a choice made in view of other aircraft routes.
No, normally they are made of water.
cirrus
The question makes no sense. Altitude has nothing at all to do with black hole formation. "Altitude" really only has any significant meaning in terms of Earth and humans, and it is as far as we know absolutely impossible to "make" a black hole at any altitude.
Altitude affects the composition of clouds because the troposphere is very cold, hence the clouds up higher are made of ice crystals.
Magnitude Pholositude <----(I think I made that up)
The higher you get in the atmosphere, the more cold it is. For example, the earth's core is very very hot, and it gets colder the more away you are from it. Or something like that. :P.
Altitude affects the composition of clouds because the troposphere is very cold, so the clouds up higher are made of ice crystals. The clouds in the lower sections are made of water droplets or a mixture of water droplets and ice crystals.