When you have marble near your city and you take the time to research and build a Quarry you get a bonus of 25% to Wonder Production. If you hover over the Production number in the city screen it breaks it down to which bonuses you are receiving.
As for what happens when a A.I. beats you to a Wonder, it gets converted to gold.
As for what happens when a A.I. beats you to a Wonder, it gets converted to gold.
