forgive my ignorance, but where is the money coming from?

so i understand that people can buy bitcoin via coinbase. they send in their USD and get bitcoins.

then there are others that mine their bitcoins. they are rewarded these coins but no USD have been put into the exchange.

so now, this means there may be more coins than USD to support it when you want to cash out. isnt this the definition of a ponzi scheme?

where is the money - actually fiat to spend on every day goods - coming from when the price of bitcoin explodes?

Cryptoflame