Complex sentence: Fleeing for their lives, Tarzan and Jane are forced to enter a mysterious valley, which has become under the effects of the meteor's unique energies for millions of years, causing bizarre mutations in the local flora and fauna.
Split into simpler sentences: Fleeing for their lives, Tarzan and Jane are forced to enter a mysterious valley. This particular stretch of the jungle has been under the effects of the meteor's unique energies for millions of years, causing bizarre mutations in the local flora and fauna.