Why are astronomers looking for evidence of ancient water on mars?

I am pretty sure they are looking for ancient water on mars, because they are trying to see if mars could be a habitable zone for humans to live

But the truth is, that right now, well... if humans were to live on mars, they would only last on that planet for possibly 40 or 80 seconds unless they have on a suit.

burning of wood and coal

explanation:

the panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in earth's temperatures over the past 50 years.

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.