They would know if they see anything like traces of water or anything else that would be nessecary for a living organism to have. They look for these with technology like the hubble telescope as well as the drone on Mars to gather as much information as possible.
Explanation:
why u want to know why u disturb ur mind by things which are already written in books
however the Question is not clear, but, the geosphere is defined as the natural environment we live in. it also controls the minerals distribution, soils and rocks and generate natural hazards that shape the land and impact the lives on earth.
Birds-Migratory
Freshwater Fish-local endemic
Large predators-sparse distribution
Small leaves protect desert plants from animals that eat plants.
