Tearfall

The Tearfall, also known as ileleste (falling rain, in elven), the changing of the stars, the seven-turn winter, or the month of mist, was a planet-wide disaster that struck Abeir-Toril in the final millennium of the Days of Thunder. It was widely believed dragonkind was created as a consequence of the Tearfall.

History
According to the Parwiccan Cycle, a devastating meteor rain fell in -31000 DR, creating a series of natural catastrophes across the planet that destroyed whole continents in earthquakes, fires, and windstorms, rearranging even the position of the seas. Ancient sarrukh accounts called this event the "changing of the stars." Due to the catastrophe, the four Inner Seas merged together to form the Sea of Fallen Stars. In both the Parwiccan Cycle and the giants traditions, the meteors were actually dragon eggs from which the varied races of dragonkind were born.

Scholars from Candlekeep had the theory that those natural catastrophes were the consequence of a comet or an ice moon (possibly one of the Tears of Selûne) that fell from the sky and devastated much of the planet, and referred to this event as the Tearfall. According to their theory, the dramatic climate change that followed quickly brought an end to the batrachi civilization and allowed the rapid evolution of proto-dragons into the various dragon species.

The red dragon's creation myth compiled in the Book of the World tell a similar history, in which the dragon deity Asgorath casted down an entity known as Zotha after creating the world and then she proceded to create dragonkind.

According to abeiran scholars, however, the Tearfall was actually caused by the actions of the batrachi. As they were losing their war against the titans, they performed a powerful summoning ritual and released several primordials from their ancient prisons. The gods quickly moved against their ancient foes, and were those battles that caused the worldwide catastrophes that destroyed the batrachi civilization. A primordial known as Asgoroth the World-Shaper, determined to destroy the world if she couldn't control it, thrown an ice moon to the planet creating the Sea of Fallen Stars. Before the world was completely destroyed, Lord Ao intervened and sundered Abeir-Toril into two twin worlds, Abeir and Toril, giving the former to the primordials and the later (the original world) to the gods, ending the conflict.

Nobody knew for sure if Asgoroth actually thrown dragon eggs to the world when she casted down the ice moon, although dragons revered Asgorath as the creator of their race. A similar event happened in 1374 DR, when many dragon eggs fell from the sky across Faerûn on an unusual year-long meteor rain, after the dragon population was greatly reduced in number in the last Rage of Dragons. Most of the eggs were recovered by the followers of Tiamat, a few by the followers of Bahamut, and the ones that weren't found either hatched on their own or were lost.