Since it appears that the coasts of North and South America would fit together with the coasts of Africa and Europe, perhaps they once did.
So if we take the distance between any given point from the East Coast of North America to its corresponding midway point along the Mid-Atlantic Ridge (half-way point to Europe), this gives us the distance that the Continents have traveled.
Then we simply divide this distance by our 200 million year "date" to arrive at the (assumed) distance that the Continents are still moving apart each year, or so the theory goes.
The figure is around five feet per century or 0.6 inches per year.
Since we have never witnessed rapid movements of huge landmasses over the surface of the earth, many think that it must have taken many millions of years for the continents to separate.
When one gets beyond the dogmatic parroting of popular (i.e.
evolutionary) "science" publications, it becomes increasingly clear that virtually all radiometric dating methods are highly questionable and subjective.
However, the dating of ocean bottom sediments by radiometric methods is even more questionable.
They base this on present day earthquakes and radiometric dating of ocean bottom (igneous) rocks.
Since present day earthquakes only move adjoining faults from one to five inches per year (on average), it is assumed that this must have been the case throughout the earth's past.
This assumption would be reasonable except for two things: For these reasons it is difficult, if not impossible, to estimate how long it took for the continents to separate.
In other words, this "clock" is invalid simply because the 200 million-year "age" of the Atlantic ocean is not based upon any measurable movement at the Mid-Atlantic Ridge, but rather upon the (assumed accuracy of) radiometric dating of ocean bottom rocks.