Here's why:

* The troposphere is the lowest layer of Earth's atmosphere. It's where we live and where most of the atmosphere's mass is concentrated.

* Weather phenomena like clouds, rain, wind, and temperature changes happen within the troposphere because it contains most of the atmospheric water vapor and has the greatest temperature variations.

* The upper layers of the atmosphere (stratosphere, mesosphere, thermosphere, exosphere) are too thin and have too little water vapor to support weather as we know it.