The word Antediluvian, a big word with two words therein. (1) Ante - meaning, before. (2) diluvian or deluge - meaning a severe flood. So, basically when you say Antediluvian, you are saying before the flood. Precisely the Flood during the time of Noah. This is better to say than Noah's flood. For Noah wasn't responsible for the Flood. The Flood was due to the increasing corruption on Earth. For reference, this is found in Genesis chapter 6. The period of the Antediluvian age was from creation as we know it, until the door of the Ark was shut and the rain and the deluge came.
This period or the Antediluvian dispensation (meaning a particular time) could be divided into two parts: (1) At the dawn of creation, and the (2) fall of man from the garden and until the flood.
Dealing with the first, at the dawn of creation, all was good. This is a phrase used with repetition throughout the account of creation, denoting, everything God made was good. However, after the fall of man, things began to change. An example would be, the children born, were born in the image of their father, not in the image of God as it was intended to be. This is why when a baby is born, the baby is already aging. The consciences of men were the delight of their fulfillment, but without God conscience, their desire was evil. As recorded in Genesis 6:5, the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. That is to say, the human race became a reprobate in a depraved world. Or as a commenter puts it:
Violence, profligacy among the lower, and cruelty and oppression among the higher classes, being only predominant. All the imaginations of their thoughts were evil - the very first embryo of every idea, the figment of every thought, the very materials out of which perception, conception, and ideas were formed, were all evil; the fountain which produced them, with every thought, purpose, wish, desire, and motive, was incurably poisoned. All these were evil without any mixture of good.
The population of the human race at this point in time was on a rapid increase than ever before. Imagine a world where the life expectancy was as high as 600-900 years. A single individual could have over 100 children in his or her lifetime, excluding grandchildren. These figures are not a miscalculation or fable. The body was created originally to live forever. Hence, the human body, replenishes and refresh itself every so often. From the outside to the inside, the skin is renewed every 2-4 weeks. Certain cells like colon cells are refreshes in four days. The white blood cells take about two years to regenerate. The liver renews itself at least once within two years.
Back to our text, at this point in time, sin was at its initial stage, infiltrating and wearing down the human race. Therefore, these men and women lived a long life. Sadly so, the majority was evil, from their youth and upward. Therefore, evil begot evil. With the unquenchable thirst of evil desire in the hearts of men, the presence of God was absent.
There are many things about this time frame, but the little we do know gives an insight to the harmony of the Word of God, and a perspective of the earth. For an example, Adam, the first man, was alive. Likely he heard of what was coming (the Flood) as well as others who were alive during this time, Enoch will be another. However, this doesn't mean Adam died in the Flood.
The earth likely took on a different form after the Flood, in terms of physical divisions and partitions. We are told in Genesis 7:11, the fountains of the great deep were broken up. The result was the rise of water from beneath the surface of the earth. The Flood wasn't just rain water turning into a flood. It was a catastrophic event, with earth movements and eruptions. It was a time of tribulation. The implication of the Greek word for tribulation denotes the act of pressing together or squeezing. This was the condition of the earth, as the waters from beneath broke forth, gushing out. The waters from above were released, causing immense pressure, crushing and destroying everything therein.
Now, before the creation of the earth as we know it, water was everywhere (Genesis 1:2) During the process of creation, God divided the waters. (Genesis 1:7) Thus, we read, God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. However, the law that held the firmament in place, was withdrawn, causing a massive crushing of water on the earth.
Looking up into the sky, there is a great expand, this is the firmament, beyond that, are the clouds, which consist of oxygen and hydrogen. Electric spark or lightning, passing through these airs, decomposes them and converts them to water causing rain. However, this was like none other rain. The Scripture described the scene as the windows of heaven were opened. Meaning a far greater downpour of rain than we are accustomed to. Consider a little spark of lightning causes rain upon a tiny portion of the earth. However, on a far greater scale, when the windows of heaven are open, imagine the scope of the lightning or the continuation thereof, and the loudness of such roaring thunder that follows. A horror to the scene for those who faced judgment. Slow is the judgement of God, but swift is its action.
Blessed are those who accept His will, such was Noah and his family. During the of time judgment, God is with those who look on to Him. For we read in Genesis 7:1, the LORD said unto Noah, Come thou and all thy house into the ark; for thee have I seen righteous before Me in this generation.
The verb "come" denotes the presence of the Lord was already in the ark. Hence, He said to Noah and his family, come in.
For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ.
(1 Thessalonians 5:9)