Perhaps you want to take a look at this?
Sooner vs Earlier
I know the difference between early and soon, but with earlier and sooner I am not sure. Please could you explain what the difference is?
So they are not interchangeable except in certain cases where both are modifying a verb having similar meanig; as:
His reply reached him sooner/earlier than mine..
When would you like to meet? The sooner/earlier the better. (adverb; in or within a short time than expected)
Not in this case:
No sooner had he got home than the rain stopped
When used as adjective, the question of sooner does not arise; as:
Here's a dish I prepared earlier (adjective; before the usual, expected or planned time)