AND IN THIS CORNER... LIVE!
We saw earlier that life as we know it on our planet, began with and in the water. Water has a key role in our kind of existence. Consider that we humans are composed of seventy percent of that element; we could almost say that we are sea animals adapted to the surface.
Well, we must place ourselves there and think that, the planet is cooling, the water remains liquid longer, and it is accumulating in the lowest places by simple gravity simultaneously.
This initial ocean, it seems, was just one and so were the lands -as continents.
Science calls today that super-continent Vaalbara-Pangaea  .
Pangaea does not remain as the only continent but gets fractured and its segments drift, sail so to speak on the molten lava beneath the crust and lead to the continents we know today.
Let's tell now tell a racconto and put all these facts in perspective.
Note that life, to evolve, develops first in the sea and then migrates to the land, while the supercontinent Pangaea-Vaalbara breaks and moves across the globe to fill the places we find familiar today.
At sea, where life generated animals, plants were also created, which moved inland and became land -dwelling vegetation, trees, grass, etc. ..
Some of the marine animals that had "come out" to land, while evolving, returned to the sea where they continued their evolution-e.g. cetaceans (whales, dolphins, etc.).
Other primeval animals became used to living on the surface and resulted in the famous dinosaurs, who reigned on the planet for about one hundred and sixty million years.
I do not want to overwhelm or drown you with the history of our world -many of you are certainly aware of it- but it is important we refresh what we know and try to notice certain "details" that are essential clues for understanding the topic at hand...