Have occurred on average every 500,000 years over the past 65 million years of earth's history

Magnetic Reversals/ Flips

Explanation:

Magnetic Reversals/ Flips are a shift in the magnetic field of the Earth resulting in alignment of the magnetic north with the geographic south and alignment of the magnetic south with the geographic north.

The Earth's magnetic field has experienced several polarity reversals as a matter of geological record. In average, there have been 4 to 5 reversals every million years over the past 10 million years.

Many times in the history of Earth, for example during the Cretaceous period, when there were no reversals, there were much longer periods. By fact, reversals are not linear and definitely are not periodic. Therefore, only the average reversal time can be spoken about.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.