Answer:
To protect the Earth and the living organism from ultraviolet radiation, heat, and to let the oxygen inside the atmosphere.
Step-by-step explanation:
An atmosphere is a gas layer that surrounds a planet. Especially on Earth is the layer that allows life inside the planet. It maintains the heat of the Sun outside along with the ultraviolet radiation and the solar wind, all things that could harm all life inside the Earth.
I hope this answer helps you.