"manifestly, noticeably," 1799, from marked + -ly (2). "A favorite 19th c. adverb" [OED].
Entries linking to markedly
marked adj.
"having a mark," Old English gemearcodan (see mark (v.)). Meaning "clearly defined, easy to distinguish" (pronounced as two syllables) is from 1795. Related: Markedly. Marked man "one who is watched with hostile intent" is from 1769.
-ly 2
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.