Here's why:
* Early Earth was too hot: The early Earth was a very hot, molten ball, and any water present would have quickly evaporated into space.
* Asteroids and comets: These celestial bodies are known to contain significant amounts of water ice. When they collided with the early Earth, the impact would have vaporized the ice, which then condensed to form oceans and other water bodies.
* Isotopic evidence: The ratio of hydrogen isotopes in Earth's water is similar to that found in comets and some types of asteroids, suggesting a common origin.
However, some scientists believe that a portion of Earth's water could have come from volcanic activity, as water molecules are present within Earth's mantle.
It's important to note that the origin of Earth's water is a complex and ongoing area of research. While the asteroid/comet theory is currently the most favored, other sources might have contributed, and more research is needed to fully understand this fascinating aspect of our planet's history.
