Overall, there was no unicell organisms popping into existence. They do not just get created by nature. It doesn't happen today nor did it happen in the past. A waterworld 3.2 B yrs ago would've dissolved them if it happened, but didn't. There was no 3.2 B yrs ago. That is just the difference is doing radiometric dating.
Yet, we had at that point in time circa 2458 BC, a whole world that went so evil that innocent people were in danger. This was not acceptable for a loving and just God. God contacted Noah because he was still one of the good people of faith and gave him the dimensions of building an ark. It took Noah and his family 100 years to build the ark. People lived longer back then. Just a little before his global flood, God shortened people's lives to 120 years. Thus, the stage is set. The Ark Encounter explains the details and circumstances and that an ark can be built and be seaworthy of its size. It also explains how God used natural selection and gathered all the animals 2 x 2. Thus, this is what has happened before your question.
Hetr is how the flood waters came to be. They came from 40 days and 40 nights of rain. During this time, there was an earthquake on the seafloor and up rose the fountains of the deep or the ocean waters that were inside the Earth. There are those who think there was a canopy of water in the sky. This was their firmament that separated light and dark on the 2nd day. It may just have been clouds, in which case all we have is the rain storm for 40 days and 40 nights. We see from Bill Nye's video in #118 that mountains were formed from the sea floor. We also think that Pangaea was was broken up during this time into seven continents. There may be some connection of why one was broken into seven as it comes into play during end times. I dunno. Thus, the waters came from above and below and this covered the entire Earth. Flowing water is very powerful and a flood is one of the weather catastrophes that could kill the most people. A global flood would kill everybody who was unprepared. Even then, I think the rapid flooding would capsize their boats.
Afterward, there was a change in Earth's topography due to the catastrophe of the global flood. The mountains such as the Mt. Everest and the Himalayas that already existed rose even higher as the flood waters surged over its peaks and created a deeper valley below. The evidence we have for this is that Mt. Everest and the Himalayas are one of the highest mountain ranges on Earth and it takes skill and courage to climb to the top. We also have the valleys that were formed and the waters flooded in and it is shown by the deepest oceans that we have and its difficult to go that deep to study. We find exotic sea creatures that somehow have adapted to live at those depths. Humans cannot just go dive that deep. They would need special equipment.
As for the waters, where did they go afterward? They formed our seas that we have now. The waters are still here and we have an planet covered with 3/4 ocean water. Thus, the entire topography of the Earth changed with the global flood and it explains the rapid change in our topography to this day. This is how our mountain ranges and depths of our oceans formed. It wasn't glaciers taking millions of years. We find underwater and buried civilizations all over the world. They were advanced civilizations, as well, and not stone age cave dwellers.
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