The amazing feat of red blood cell production is scientifically termed "erythropoiesis". This process occurs in your bone marrow, which is basically a crazy goo filled with a type of stem cell that differentiates into all the types of blood cells your body produces. When a stem cell in your bone marrow decides it wants to grow up to be a red blood cell, the process of maturation takes a few days. However, because this process is happening continuously, 2 million red blood cells are ready to break out from their birth place in bone marrow and into your bloodstream every single second.
To make things even more mind-boggling, consider how many oxygen molecules can be transported on each new red blood cell that you produce. Red blood cells are like giant rafts for hemoglobin, a protein that binds to oxygen allowing it to be efficiently transported throughout your body in a matter of seconds. A single red blood cell contains approximately 250 million hemoglobin molecules. Each hemoglobin molecule can bind to 4 oxygen molecules. This means that 1 BILLION oxygen molecules can be transported on a single red blood cell.
Yeah, so next time you are watching the Kardashians, don't feel guilty. Not only are you processing sensory input from your television, you are also producing millions of oxygen hoarding red blood cells per second. Now that's what I call multitasking.