I’ve heard this before, but I don’t see the pattern in the numbers at all!
Major extinction events:
542 million years ago
517 million years ago (25 million years later)
502 million years ago (15 million years later) *
488 million years ago (14 million years later) *
440 million years ago (48 million years later)
373 million years ago (67 million years later)
359 million years ago (14 million years later) *
260 million years ago (99 million years later)
252 million years ago (8 million years later)
201 million years ago (51 million years later)
145 million years ago (56 million years later) *
66 million years ago (79 million years later)
34 million years ago (32 million years later)
14 million years ago (20 million years later)
current (of course, 14 million years later) *
Several seem to be some multiple of 14 years apart from the previous one, but there’s no multiple of 14 between such pairs, so it just seems like a byproduct of randomness.
Just because the comets in the distant Ort Cloud may get stirred up every 25-26 or so million years, doesn’t mean comets from there will necessarily come crashing into earth each time. There are many possible causes for mass extinctions, and it could well be a combination of various factors.