I would be very grateful if anyone could explain me the difference between the adverbs "deep" and "deeply" in general, and apart from that , I found the following sentences and I don´t understand why they use "deep" in the first three and "deeply" in the last one. Thank you in advance. They dived deep into the ocean. The gold lies deep in the earth. He went on studying deep into the night. The dog bit deeply into his arm.