Here I am not much concerned with the regular churning of sea water taking place, but how and when it stops and when it starts all over again.
Yes, as per Puraans the churning of water stops and then restarts and the entire cycle of oceans churning, then churning stopping, and again restarting is anything of the duration of 1.5 to 4.0 million years.
So the easiest thing to start the post, is from the current period.
Pollution, indiscriminate exploitation of natural resources has rendered this earth vulnerable for worldwide floods because of green house effects.Know more about Greenhouse effect, link: https://en.wikipedia.org/wiki/Greenhouse_effect
They forget that ....
nature itself plays an important role to check such hazards and had done so quite consistently. If checks and balances from nature were not there earth would have been destroyed long back.