Contradiction with Genesis 6:19-20
These verses state that Noah took two of every kind of living creature into the ark, which implies they were alive, but Genesis 8:6 sets a timeline well after creatures entered the ark.
Genesis 6:19-20: And of every living thing of all flesh, two of every [sort] shalt thou bring into the ark, to keep [them] alive with thee; they shall be male and female.
Contradiction with Genesis 7:4
Here, God states He will cause it to rain for forty days and nights, conflicting with the timeline implied by Genesis 8:6 where rain had already stopped before this verse.
Genesis 7:4: For yet seven days, and I will cause it to rain upon the earth forty days and forty nights; and every living substance that I have made will I destroy from off the face of the earth. [destroy: Heb. blot out]
Contradiction with Genesis 7:17
This suggests flooding for forty days, while Genesis 8:6 occurs after this period with no indication of rain.
Genesis 7:17: And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lift up above the earth.
Contradiction with Genesis 7:24
It states the waters prevailed for 150 days, which contrasts with Noah opening the window of the ark after the earlier rain timeline implied in Genesis 8:6.
Genesis 7:24: And the waters prevailed upon the earth an hundred and fifty days.