Was watching few days ago a program on the NGC about comets and how water formed on earth. A British scientist was interviewed and his statement was as follow:
"Billions of years ago the earth was bombed with comets ( who allegedly carry oxygen found through spectrometry).The surface of the moon is a perfect representation of what happened then. We just now don't have the same evidence to show regarding the earth".
So, they speak with absolute certainty of something they can't support or justify.
And then if the same thing happened to the moon ( bombed with comets) then why there isn't any water or oxygen on it?