2. Make a natural layer of a green house gases surrounds the earth. It keeps the earth warm. From the book in the library, learn about the gases that forms this layer. What would have happened if the layer was not there? You can take help of various books or internet.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

if you're asking what comes out, it's steam.