Genesis 6:4

6:4 The Nephilim were on the earth in those days (and also after this) when the sons of God were having sexual relations with the daughters of humankind, who gave birth to their children. They were the mighty heroes of old, the famous men.

Genesis 6:11-12

6:11 The earth was ruined in the sight of God; the earth was filled with violence. 6:12 God saw the earth, and indeed it was ruined, for all living creatures on the earth were sinful.