Out of this world: did Earth’s water come from icy comets and grains of space dust?

New British research backs theory that parched planet's water all came from extraterrestrial source

It covers three quarters of the surface of the Earth and gives our planet its distinctive blue complexion when viewed from outer space. But the source of the liquid water that sustains our seas and which has nourished life on our world for eons is a subject of major scientific debate.

Some researchers argue that water in some form has been present on our world ever since it coalesced out of swirling clouds of dust and gas 4.5 billion years ago. Earth has always been provided with a reservoir, in short.