system
Given the following post, respond as if you're commenting on Reddit:
human
As Pangea began to drift apart, did the bodies of water that would become known as today's oceans begin as narrow channels and grow over time, or did they come about later on?

I suppose that I'm asking, was there a time you could wade from "North America" to "Africa"?  In the same vein, was there a time when if I stood on the southern coast of Asia, I would see the Indian subcontinent a few kilometres away, very slowly (imperceptably, no doubt) approaching?
gpt
There's no single answer. In some cases, the splitting of continents would have occurred so that seawater filled in as it happened. In others, the splitting progressed further before reaching a point where existing ocean could have entered.

When the Atlantic rift opened, it did so along a series of rift valleys in what are now eastern North America and northwest Africa. Most of these failed to form large rifts and infilled only with sediment from terrestrial sources (rivers, etc.). But others connected to form a longer rift that is now the mid-Atlantic ridge.