• Question: I watched a documentary about a comet and they said the Earths water could have come from comets could this have happened?

    Asked by billytheshark to Alex, Ali, Kerry, Philip, Theo on 18 Nov 2014.
    • Photo: Alison Thomson

      Alison Thomson answered on 18 Nov 2014:

      Absolutely! Comets are really cold, and quite a bit of them is made up of ice, so in the past 4 billion years they’ve been colliding with earth and the ice has melted, giving us our water!
      Although there are other theories of where the water came from that suggest the water was here in the first place.

      Great question!

    • Photo: Kerry O'Shea

      Kerry O'Shea answered on 18 Nov 2014:

      I think there are different opinions about this. People have suggested that some of the Earth’s water came from comets, but not all of it. Most of the water on Earth was probably already there during the early evolution of the planet. People have measured the ratio of deuterium to protium in the water of the Earth’s oceans and compared it to that of comets and protoplanets to come up with theories for the origin of water on Earth. However, this ratio could have changed over the lifetime of the Earth, so it’s impossible to know for sure.

    • Photo: Philip Ratcliffe

      Philip Ratcliffe answered on 18 Nov 2014:

      Well, it’s certainly possible and many scientists have theorised this. But since it would have happened a long time ago it’s very difficult to prove it for sure either way. However, as a physicist I know that when something is reasonably possible (plausible) then usually it really does occur. Having said that there is an awful lot of water on Earth so I think it’s also reasonable to assume that much of it was already here or at least formed on Earth from combining hydrogen and oxygen.

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