I shall be late because I missed the earlier train.
I'd seen earlier (in the day).
adverb
comparative form of early: more early
previously; before now; sooner
From what I vaguely saw earlier this morning, when I had just woken up and was tidying my bed, a tall, bulky person left an unfamiliar box at my front door.
I shall be late because I didn't start earlier.
They were looking for some measuring equipment they had placed in the ice earlier.