how earth was formed 

Dear Student,

The universe started out with only two elements, hydrogen and helium gas, which formed stars that burned these elements in nuclear fusion reactions. .Billions years ago supernova exploded, pushing a lot of its heavy-elements into a nearby cloud of hydrogen gas and interstellar dust. The mixture grew hot and compressed under its own gravity, and at its center a new star began to form.

That new star became our Sun, and the glowing disk gave rise to Earth and its sister planets.

This was the initial events that lead to the formation of earth. The atmosphere of earth was formed by the process described by yukti.

Hope this will help you,

Cheers !!