The first great cataclysm is "The Birth of Life" in the form of the Firstborn. There is no indication of how or why life began, but it was initially elemental who arose in Tratho. These Firstborn do not age or die, they do not reproduce. Firstborn life began spontaneously, by all accounts. The Birth of Life is marked as a cataclysm because before life there was no suffering. All was equal and in balance. However, there is no escaping suffering for the living.
The second great cataclysm is "The Release of the Challa". The Challa are Firstborn of Fire. They know only consumption due to their immaterial nature. The Challa were imprisoned by the other Firstborn when all attempts to sate their desire for consumption failed. They were released when Tratho was stricken by a meteor that cracked their prison. This same meteor planted the seeds for the third great cataclysm.
The third great cataclysm is "The Birth of Chaos". Though the Challa were eventually returned to their prison under the crust of Tratho during the Second Age, the elements that rode in on the meteor circulated throughout the system until they eventually give rise to Chaosborn. The Chaosborn are not born with an innate affinity for any native element, but they can develop it. Because of this, the balance of the elements is disrupted when a disproportionate number of Chaosborn develop affinities for one or two elements.