Timing of the Deluge. The Deluge did not come suddenly without warning. Years of time were spent building the ark, time that Noah the “preacher of righteousness” also used in warning that wicked generation. (2Pe 2:5) Finally the time limit was up “in the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month.” The “male and female of every sort of flesh” had been brought into the ark with Noah’s family, as well as a sufficient food supply for all, and “after that Jehovah shut the door.” Then “the floodgates of the heavens were opened.” (Ge 7:11, 16)

Noah and his family entered the ark in the 600th year of Noah’s life, the 2nd month (October-November), the 17th day. (Ge 7:11)

In the log that Noah kept, it appears he used months of 30 days each, 12 of them equaling 360 days. In this way he avoided all the complicated fractions involved had he used strictly lunar months consisting of slightly more than 29 1⁄2 days. That such calculations were used in the account is evident from the fact that a five-month period consisted of 150 days.​—Ge 7:11, 24; 8:3, 4.

The Floodwaters. It has been said that if all the moisture in the atmosphere were suddenly released as rain it would not amount to even a couple of inches if spread over the earth’s surface. So from what source was this vast deluge of Noah’s day? According to the Genesis account, God said to Noah: “Here I [Jehovah] am bringing the deluge [or, “heavenly ocean”; Heb., mab·bulʹ] of waters upon the earth.” (Ge 6:17, ftn) Describing what happened, the next chapter says: “All the springs of the vast watery deep were broken open and the floodgates of the heavens were opened.” (Ge 7:11) So overwhelming was the Deluge that “all the tall mountains that were under the whole heavens came to be covered.”​—Ge 7:19.

Where did this “heavenly ocean” come from? The Genesis account of creation tells how on the second “day” Jehovah made an expanse about the earth, and this expanse (called “Heaven”) formed a division between the waters below it, that is, the oceans, and the waters above it. (Ge 1:6-8) The waters suspended above the expanse evidently remained there from the second “day” of creation until the Flood. This is what the apostle Peter was talking about when he recounted that there “were heavens from of old and an earth standing compactly out of water and in the midst of water by the word of God.” Those “heavens” and the waters above and beneath them were the means that God’s word called into operation, and “by those means the world of that time suffered destruction when it was deluged with water.” (2Pe 3:5, 6) Various explanations have been offered as to how the water was held aloft until the Flood and as to the processes that resulted in its falling. But these are only speculative. The Bible says simply that God made the expanse with waters above it and that he brought the Deluge. His almighty power could easily accomplish it.

Effect on the Earth. With the Deluge great changes came, for example, the life span of humans dropped very rapidly. Some have suggested that prior to the Flood the waters above the expanse shielded out some of the harmful radiation and that, with the waters gone, cosmic radiation genetically harmful to man increased. However, the Bible is silent on the matter. Incidentally, any change in radiation would have altered the rate of formation of radioactive carbon-14 to such an extent as to invalidate all radiocarbon dates prior to the Flood.

With the sudden opening of the ‘springs of the watery deep’ and “the floodgates of the heavens,” untold billions of tons of water deluged the earth. (Ge 7:11) This may have caused tremendous changes in earth’s surface. The earth’s crust, which is relatively thin and varied in thickness, is stretched over a rather plastic mass thousands of kilometers in diameter. Hence, under the added weight of the water, there was likely a great shifting in the crust. In time new mountains evidently were thrust upward, old mountains rose to new heights, shallow sea basins were deepened, and new shorelines were established, with the result that now about 70 percent of the surface is covered with water. This shifting in the earth’s crust may account for many geologic phenomena, such as the raising of old coastlines to new heights. It has been estimated by some that water pressures alone were equal to “2 tons per square inch,” sufficient to fossilize fauna and flora quickly.​—See The Biblical Flood and the Ice Epoch, by D. Patten, 1966, p. 62.

In times past, certain primitive people (in Australia, Egypt, Fiji, Society Islands, Peru, Mexico, and other places) preserved a possible remnant of these traditions about the Flood by observing in November a ‘Feast of Ancestors’ or a ‘Festival of the Dead.’ Such customs reflected a memory of the destruction caused by the Deluge. According to the book Life and Work at the Great Pyramid, the festival in Mexico was held on the 17th of November because they “had a tradition that at that time the world had been previously destroyed; and they dreaded lest a similar catastrophe would, at the end of a cycle, annihilate the human race.” (By Professor C. Piazzi Smyth, Edinburgh, 1867, Vol. II, pp. 390, 391) Notes the book The Worship of the Dead: “This festival [of the dead] is . . . held by all on or about the very day on which, according to the Mosaic account, the Deluge took place, viz., the seventeenth day of the second month​—the month nearly corresponding with our November.” (By J. Garnier, London, 1904, p. 4) Interestingly, the Bible reports that the Flood began “in the second month, on the seventeenth day of the month.” (Ge 7:11) That “second month” corresponds to the latter part of October and the first part of November on our calendar.