The Nephilim were on the earth in those days--and also afterwards--when the sons of God went to the daughters of men and had children by them. They were the heroes of old, men of renown.
So the LORD said, "I will wipe mankind, whom I have created, from the face of the earth--men and animals, and creatures that move along the ground, and birds of the air--for I am grieved that I have made them."
So God said to Noah, "I am going to put an end to all people, for the earth is filled with violence because of them. I am surely going to destroy both them and the earth.
I am going to bring floodwaters on the earth to destroy all life under the heavens, every creature that has the breath of life in it. Everything on earth will perish.