Earth is a unique planet, with 71% of its surface covered by water. Where do these 1.4 billion cubic kilometers of life-giving moisture, essential for life, come from? Scientists have been searching for the answer to this fundamental question for decades. For a long time, it was believed that the water was brought by comets. However, in 2014, the Rosetta mission to comet 67P/Churyumov–Gerasimenko revealed that the deuterium-to-hydrogen ratio there differs from that found in Earth's oceans. This significantly reduced their contribution. Asteroids turned out to be a much more likely source. Carbonaceous chondrites, such as the Murchison meteorite that fell in Australia in 1969, contain up to 20% water. Their isotopic composition is remarkably close to that of Earth's water. There is evidence that some water has always been present within the Earth. Studies of mantle minerals indicate that the oceans may have formed as a result of volcanic degassing during the Hadean era, more than 4 billion years ago. It's likely a combination of sources: asteroids, comets, and the internal outgassing of the early Earth. Every drop of water is the result of billions of years of cosmic history. Cherish this priceless blue pearl!