What part of speech is early?

Answer 1

its an adjective

No, it's a noun (when you can count it: ie. The summer mornings make you feel full of....). It can also be an attribute (hence the confusion with an adj) : ie. The morning paper is ....
In the morning we like to.... - this is a different situation, when the entire group functions as an object.

Answer 2

"Early" can be an adjective, e.g. the early morning. It can also be an adverb, describing when something happens, e.g. "early in the morning".

Answer 3

Morning can be a

noun: It was a sunny morning.

adjective: It is time for morning prayers.

Answer 4

adjective