Genesis 6:1-7 tells us why God decided to destroy all creation with the flood. The Bible reads “And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually” (Genesis 6:6 KJV). Man’s “wickedness” was not profoundly explained in the Bible. However, we can generalize that sin was rampant during those days. One of man’s wickedness described was the unholy union of sons of God and daughters of men. It is believed that the “sons of God” and the “daughters of men” are referring to the descendants of Seth and Cain respectively. We can also assume that man had forgotten to burn offerings unto the Lord since burnt offerings were done during the time of Adam and after the flood. Nevertheless, God repented creating man on the earth.
However, Noah found grace in the eyes of the Lord (Genesis 6:8 KJV). God warned Noah about the destruction coming and commanded Noah to build an ark giving specific details (Genesis 6:14-16 KJV):
Length – 300 cubits
Width – 50 cubits
Height – 30 cubits
Noah made the ark just like God described it. God then commanded Noah to gather one pair of every kind of creature and keep them alive. In addition he was to gather seven pairs of clean beasts.
Genesis 7 describes how the flood took place. It was in the six hundredth years of Noah’s life when the flood finally came. Seven days prior, God commanded Noah to get inside the ark together with his wife, sons, sons’ wives, and all the creatures God commended Noah to gather. On the seventeenth day of the second month of the six hundredth year of Noah’s life (2348 BC on the Bible Timeline Chart), the rain poured and the windows of heaven were opened (Genesis 7:11 KJV). The rain continued on pouring over the earth for forty days and forty nights. And this killed all creatures not on the ark.
The flood lasted for one hundred and fifty days (Genesis 7:24 KJV). On the seventeenth day of the seventh month of the six hundredth year of Noah’s existence, the ark rested on the mountains of Ararat and the waters continually subsided until the tenth month (Genesis 8:4-5 KJV).
On the six hundredth and first year of Noah’s existence, on the first day of the first month, the covering of the ark was removed and Noah saw that the face of the ground was dry (Genesis 8:13 KJV). On the twenty seventh day of the second month of that same year, God spoke to Noah and commanded him, his wife, his sons, his sons’ wives and all other creatures to be fruitful so that the earth would be filled again (Genesis 8:14-19 KJV).
Noah then built an altar unto the Lord and took all the clean beasts and fowls and gave burnt offerings unto the Lord. God smelled the sweet savour and said in His heart that never again would he curse the earth for man’s sake. In Genesis 9:8-11 God said to Noah and his sons, “And I, behold, I establish my covenant with you, and with your seed after you, and every living creature that is with you… neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.” As a token of that covenant, a rainbow would be present after it rains to remind God of his everlasting covenant (Genesis 9:12-17 KJV).
References for How Long It Took To Build The Ark