Geological pulse conclusion

Geologists have been investigating a potential cycle in geological events for a long time. Back in the 1920s and 30s, scientists of the era had suggested that the geological record had a 30-million-year cycle, while in the 1980s and 90s researchers used the best-dated geological events at the time to give them a range of the length between 'pulses' of 26.2 to 30.6 million years. Now, everything seems to be in order - 27.5 million years is right about where we'd expect. A study late last year suggested that this 27.5-million-year mark is when mass extinctions happen, too.

Which of the following statements can be BEST concluded from the passage?