What is the origin of water on Earth, and does it descend from the sky?

Specialists still differ on the origin of water on Earth, and the Quran has not definitively settled the matter. Some verses indicate that water originated from the earth, such as the Almighty's saying: "He extracted from it its water." Other verses point to a celestial origin, such as the Almighty's saying: "And We sent down from the heaven water in due measure and settled it in the earth." Some contemporary scholars have combined both approaches, believing that water on Earth is partly celestial and partly terrestrial, and the matter is still under investigation.