The statement that provides the best additional evidence supporting the conclusion that continents were once joined but have drifted apart over time is:
The sequence of rock layers on Africa's western coast is almost identical to those found on South America's eastern coast.
This observation highlights geological similarities that imply a common origin, supporting the idea that these continents were once part of a larger landmass before drifting apart. The alignment of rock strata across continents serves as a strong piece of evidence for continental drift, in line with Alfred Wegener's theory.