The Great Flood was a global cataclysm that covered the whole world, killing all air breathing land animals and birds except those within the ark which Noah  had built based on a pattern given him by God Himself. The flood was the Creator's action in response to the level of violence and disinterest that the population of the world had risen.
After a period of intense rainfall and general destruction from below the floors of the oceans, the earth had been covered with water to a depth 15 cubits (about 22.5 feet) above whatever the highest mountain was at the time. This rise took a full 150 days before receding to present levels.
Destruction came from rain and activity under the surface of the seas, and perhaps, the land. After forty days and night the rain stopped but the water rose until all the mountains were covered, the water eventually receded but left much of the Earth deformed and damaged. The Great Flood occurred because of the sinfulness  of humanity at the time.
The World That Was
In six days — each having an evening and a morning in that order — the LORD God created everything that exists. The earth had been deemed "very good" by God himself. Everything worked properly, the animals co-existed while eating plants created specifically to be food.
In the highlands was the place of the Garden of Eden, from which flowed a great river that split into four lesser rivers that provided water for the rest of the world. The world was a large field, sown with all manner of plant life, but hydrated naturally by a mist rather than rain. Eden, at the center of the great continent, was especially prepared as a home for mankind, with the plan to spread to every part of the world.
After leaving Eden, Adam and Eve found a world less friendly to cultivation. The dew and groundwater was not enough to sustain the widely dispersed food sources that mankind needed. This required men and women to work much harder — to work up a sweat — to get anything near what they had in the Garden. But the command to multiply and fill the earth with people became even more important. Large families were a must in order to coax food from the ground.
The original perfection of both mankind and the world around them lent well to the success of man apart from the direct protection that was theirs in Eden. Having turned from God, mankind proved resourceful. There is no doubt that the civilization that is evident immediately after the Flood was based on knowledge acquired before it.
Though people worshiped the true God, the Creator in the early years, the descendants of Cain, with possible collaboration from fallen angels, became more and more selfish, living each day for themselves. This led to constant in-fighting and violence of the sort of Cain their father. The descendants of Seth could not escape the corruption of their neighbors. In the end, the LORD found Noah worthy of notice, choosing to show mercy upon him. With one hundred years to work, Noah would build an ark to preserve life as it would be known after the flood.
Preparations for the Flood
Back on the third day of creation, after separating light from darkness and the "waters above" from the "waters below," God had created what He called "earth" — the dry land. It had been the home to most of the animal life that mankind knew. Following the command of God, and the nature of animals in general, living things spread out over the whole world.
For over fifteen hundred years, mankind probably followed the paths of the great rivers to the furthest points of the world. At the ends of these rivers, it is likely that those travelers found the ocean beyond a very frightening place. It is probable that river crossings had taken human life along the way, so the vast ocean surrounding the dry land was in all likelihood seldom used along its shores.
By the time that Noah heard the voice of God, it had been over five hundred years since Enoch had been taken bodily to be with God. Enoch had been preaching about God's judgment coming upon the earth at the end of time. Nobody seems to have been listening. Even Noah, a righteous man, was tainted as to have to "find grace (favor) in the LORD's eyes. Sometime prior to the 600th year of Noah's life, instructions were given to Noah to build a large structure designed to be waterproof. God informed him that the world would soon experience destruction by water.
The structure was a "tebah," and is defined by its shape and purpose. The word is ancient with no certain origin. It is used once more by Moses, in his telling of his own rescue in a waterproofed basket. The English term "ark" goes back at least to the Latin "arca" meaning a chest or coffer (from arcere: to safeguard). The structure was built to float, for as large as it was, no provision was made for a foundation. The Ark was to be 300 cubits long and 30 cubits tall, where a cubit is the length between the builder's elbow and tip of his longest finger. This ratio was made even more secure by a wide base of fifty cubits. In feet, the structure was from 450'x45'x75' to 600'x60'x100' built in three stories with a window across the top and a single door that could not be opened from the outside.
Starting on the project years before his three sons could assist him, Noah (and possibly his father Lamech) procured supplies and materials over a course of decades. Then, over a period of perhaps 80 years, the four of them took advantage of the technology of their day to slowly build a structure big enough to house a small town — if its purpose weren't for more essential life forms. Long term, the task of preserving and storing seed and edible food was essential. Noah had to trust God that the plan would work. He may have been told the deadline as early as 20 years before Japheth, his oldest son, had been born. He trusted God that the duration of the flood would be tolerable for all the occupants of the ark.
As the ark was being finished, the Lord Himself was leading animals  toward the site where the barge-like structure awaited. Having been told to bring a mating pair of most land animals and birds, Noah was further instructed to bring in either seven or seven pairs of animals designated as "clean". It is probable that these extra animals were in anticipation of periodic sacrifices. It is also possible that these were the "domesticated" animals used for various purposes — beasts of burden, sources of wool, and so forth.
Finally, after the animals were all aboard, God caused the door to close. For seven days Noah and his family — his wife, three sons and their wives — settled into a routine. And then, the water came. Around the world the people began trying to find high ground. Some undoubtedly tried to break through the walls of the ark. But by the time the ark began to float the screams had surely ceased. Mankind's hope was inside the huge structure that now became a ship.
See also: The Flood: A Biblical Timeline
On the seventeenth day of the second month, in the six hundredth year of Noah's life (the Year of the World 1657) the rains began to fall. In addition, the "fountains of the deep" burst forth from the ocean floors. The creative act of the third day was dramatically reversed. Though the rain lasted "only" forty days and nights, the waters rose for a full 150 days. It took about six weeks of receding water before the ark caught on a lonely mountaintop many miles from the next highest hill that was seen on the first day of the tenth month. For another forty days, the ark rested as the waters receded even more, probably revealing other mountaintops on the horizon.
Finally, Noah sent out avian scouts: a raven and a dove. The raven, finally released from the darkness inside the ark, flew endlessly, finding floating plants and occasional carrion upon which to feed. The dove, a much more particular eater and — since it was a "clean" animal — a favored animal, came back to the ark when it could not find anywhere else to rest. A week later the dove was sent out again. That time, the dove came back with an olive leaf it had found. Seven days from that, the dove was sent out and stayed out, having found a place to make her nest.
With this proof that the world world was drying off, Noah removed the upper covering of the ark to get a better view of things. The earth had survived and the plants had taken root in a slow rebuilding of the ground cover. Noah faced the new year, the year 1658 — and 601st of his life — with faith that God was indeed with him. However, it would be nearly two months — 57 days — before God spoke once again to his servant Noah. He told him to come out of the ark onto dry land.
On the twenty seventh day of the second month, year of the world 1658, a new age began. In God's plan, the best gene pool in the world had been preserved for over a year. With instructions much like those given on the sixth day of creation, mankind, beasts and birds set out on a huge task to build a new world.
As the animals moved out into the surrounding world, Noah and his family worshiped God. Following a practice that the LORD himself had begun, Noah killed and burned "clean" animals — both birds and beasts — on an altar. As the smoke rose symbolically into the "face" of God, He was pleased. God then set down some basic ground rules. Death had become part of the experience of the earth. Where from the beginning plant-life had existed to feed all the animals, animals were now allowed to be proper food for mankind. However, killing of animals for food had one restriction: blood was not to be consumed.
That murder was disallowed was self-evident based on the characteristic violence that brought about the flood. However, the mercy shown to Cain in the beginning was not to be extended to murderers in this new world. God established the punishment for murder to be death itself. The reason for this was given as a reminder of the creation of the first man: the image of God was sacred as it was found in each human being.
God revealed His intent to Noah — that he would never destroy all mankind by water again. As long as the earth lasted, up until it would be restructured at the end of time, seasons would continue to cycle, bringing life and rest, recycling itself until all that God has planned for mankind will come to pass. Rain would come, but not to destroy the earth. Clouds would gather, but only to bring blessed water for life. God called a truce, laying down his bow in the clouds, symbolically portraying this with a new phenomenon: the multifaceted light of the rainbow.
- ↑ Genesis 6:8-9, 18; 7:1 (Link)
- ↑ Genesis 6:7, 17; 7:21-23 (Link)
- ↑ Genesis 6:5, 11-12 (Link)
- ↑ Genesis 6:6, 13 (Link)
- ↑ Genesis 1:31 (Link)
- ↑ Genesis 1:29-30 (Link)
- ↑ Genesis 2:10 (Link)
- ↑ Genesis 2:5 (Link)
- ↑ Genesis 1:28; 2:8 (Link)
- ↑ Genesis 3:17-19 (Link)
- ↑ Genesis 4:19-22 (Link)
- ↑ Genesis 10:8-10; 11:1-6 (Link)
- ↑ Genesis 4:25 (Link)
- ↑ Genesis 6:4 (Link)
- ↑ Matthew 24:37-39 (Link)
- ↑ Genesis 6:1-8 (Link)
- ↑ Genesis 5:22; 6:10, 13-14 (Link)
- ↑ Genesis 5:23-32 (Link)
- ↑ Genesis 6:8-9 (Link)
- ↑ Genesis 6:13-15 (Link)
- ↑ Genesis 6:21 (Link)
- ↑ Genesis 7:9 (Link)
- ↑ Genesis 6:20; 7:2 (Link)
- ↑ Genesis 7:16 (Link)
- ↑ Genesis 7:11 (Link)
- ↑ Genesis 7:17-24 (Link)
- ↑ Genesis 8:1-5 (Link)
- ↑ Genesis 8:6-12 (Link)
- ↑ Genesis 8:13-16 (Link)
- ↑ Genesis 8:20-21 (Link)
- ↑ Genesis 9:1-4 (Link)
- ↑ Genesis 9:5-8 (Link)
- ↑ Genesis 9:8-17 (Link)