How did water form on the surface of the Earth after the Big Bang?

Water formed on the surface of the Earth, according to current scientific theory, long after the inner worlds of the solar system developed. Current thinking must be regarded as only a stage in our certain understanding of how our world developed.

However, this is what is thought: our world was originally dry, the surface then becoming molten as result of collisions. Later collisions with wet comets and asteroids led to water forming on the surface of Earth.