So wait.
You have a hard time believing that in 4.5 billion years the earth hasn't 'used up' all its water (which you still haven't said how or why it would be used up), but you have no problem believing that it's has more than 4.5 billion years worth of hydrogen to create both water and hydrocarbons?
You have a hard time believing that in 4.5 billion years the earth hasn't 'used up' all its water (which you still haven't said how or why it would be used up), but you have no problem believing that it's has more than 4.5 billion years worth of hydrogen to create both water and hydrocarbons?