In answer to your question: yes. Humid cold pure air. By pure, I mean no contaminates until the hyrdrocarbons from the jet fuel are emitted into that pure, moist air. To form a droplet, a nucleus is needed. The hydrocarbons of the jet engine exhaust provide that nuclueus.

Hmm. America (any part of it, North America, South America) didn't become part of this until a little more than 500 years ago at the earliest. Not THOUSANDS of years. Then, it was Catholics who spread the western 'civilization' to the Americas, yet the United States hates Catholicism and says the protestant King James Bible is the true word of a non-existent god. The nation that is not supposed to push any religion only pushes protestant christian religion denying the THOUSANDS of years of Catholicism.

Lead gives you brain damage. Rock laughs.

No. Not the easily fragmented feldspar. Nice solid granite.

Oh, no no no. There are many things proven to kill you. Curare, arsenic, botulism, too much salt, not enough salt, too much water, not enough water, and on and on and on and on ...

Well, it's impossible to ban natural clouds but planes could avoid making contrails by just not flying in the zone where their exhaust would cause them. Source: I was a weatherman in the Air Force and would tell military pilots where to fly to not have a shiny line pointing to their exact location if such information could be a concern.

I never thought it about as a green house thing before though I do remember reading an article many years ago that contrails do contribute when they spread out into cirrostratus clouds.

I was a meteorologist in the Air Force and did make forecasts telling pilots at what levels to fly to avoid making contrails since having a long silver line pointing to your exact location makes sneak attacks a little difficult. Perhaps commercial airlines should make use of that information. It's usually just a few thousand foot difference. Fly a little higher or lower and problem solved.

It looks like the cage has cedar chips on the bottom which is softer than the packed dirt this creature would sleep on in the wild.