all the fountains of the great deep burst open, and the floodgates of the sky were opened. (Genesis 7:11)Not only did water fall from the sky, but the fountains of the great deep burst open— water exploded out of the ground. Doubtless, this must have been accompanied with cataclysmic earthquakes across the entire globe. If a map of the pre-flood world was ever created, it would not have been very useful after the flood.
The historical division between the pre-flood world and post-flood world is not artificial; rather, the division is almost mandatory. The flood not only marked the destruction of every lineage except for Noah's, but it marked a reshaping— a remolding of the surface of the earth. Geology (the study of rocks) can reveal a lot of information about how the earth might have looked prior to the flood (for more information on this subject take a look at the Geology section of AnswersInGenesis.org).
The floodgates of the sky refers to rain. Perhaps God gathered a massive quantity of water in the atmosphere through natural processes, or perhaps he used supernatural processes. Either way, there was an absolutely massive amount of water gathered— this is known due to the length of time for which the rain fell:
The rain fell upon the earth for forty days and forty nights. (Genesis 7:12)"Forty nights," seems to be added in order to further emphasize the length of time for which the rain fell. Seven days ago, God had mentioned to Noah this detail (Genesis 7:4). Now what God had said was being fulfilled. The first day of the rain had arrived. And if the first day was accompanied with so much destruction— with torrential downpours and water gushing out of the earth's crust, the next 39 days were sure to be jammed with similar destruction.
Noah and his household were safe in the ark. And they must have stood in amazement— gazing in awe at the power and majesty of the one true God. At the God who puts to death and gives life— at Him who wounds and Him who heals (Deuteronomy 32:39).
Noah's Timely Entry (Part 1) - Genesis 7:13-15
State of the World (2349 BC): The Flood (Part 1) - Genesis 7:11
A Short Account of the Ark's Final Preparation - Genesis 7:6-9
7 More Days - Genesis 7:4-5
The Pre-Flood World: Filled With Violence (Part 1) - Genesis 6:11-13