Owing to the changes in the gravitational forces applied by the celestial bodies, the Earth's orbit tends to change slightly and become a little more elliptical than usual every '100,000 years'.
This change in the orbit causes the Earth to move closer to the Sun and as a result, the climate on Earth gets warmed up owing to the increased proximity to the Sun.
Thus, this cycle exhibits substantial changes in the overall environment of the Earth every '100,000 years'.
