If something happens in a significant way or to a great degree, you can say it occurs markedly. If the price of milk rises markedly, you'll notice it the next time you're grocery shopping.
When the acting on your favorite bad TV show improves markedly, you might guess that all the actors took acting lessons over the summer. And if the speed limit in your city is markedly lowered, you'll feel a lot safer riding your bike around town. The adverb markedly comes from marked and its sense of "having a mark," from the Old English mearc, "sign or mark."