[antonmks]

"significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago" - it seems that periods between extinctions events are so large that you can easily fit there hundreds and even thousands of civilizations like ours. So not much to worry about, we will have plenty of opportunities to kill ourselves before a comet does us in.

[dghughes]

I'm not a math wizard but going by that pattern it seems the periods are getting shorter.

I tried to find a sequence https://www.wolframalpha.com/input/?i=415,+322,+300,+145,+33....

[mrec]

The periods (intervals between events) there would be [93, 22, 155, 112] My. That doesn't look like they're getting shorter.

[swamp40]

But they are getting closer! :)

[marcosdumay]

My bet is that is because of observation biases. We don't know a lot about distant past, and may have lost some events that we'd call great extinctions if they were recent.