He gases in earth's early atmosphere are inferred to have come primarily from

The early gasses that composed the Earth's atmosphere are believed to have derived from the volcanoes that were in huge numbers and dispersed all across the globe. They were very active, and some of them very big and with enormous capacity, and they were constantly letting gasses out, which made the first atmosphere of our planet.

Ther are many reasons.. is it a multiple choice?

Gravitational force i believe