No specialist here, but it can also grow.

Id the coin in my hand goes to you and than to me, ans this cycle repeats once per year, our Gpd is 1.

But if we do this 2 per year, our GDP is 2.

Compare this with the barter system (escambo).

We don't have the goal of trading money, but of trading goods.

If I get 1 kg of rice from my plant pee year to sell to you for 1 real, and you get 1 kg of beams, we can do this as often as you want, having only one real.

The "earth resources" plus our work is the real good being traded, not the paper