Let's break down the words now:
Sun: the heat or light radiated from the luminous celestial body around which the earth and other planets revolve, from which they receive heat and light, and which has a mean distance from earth of 93,000,000 miles (150,000,000 kilometers), a linear diameter of 864,000 miles (1,390,000 kilometers), a mass 332,000 times greater than earth, and a mean density about one fourth that of earth.
Block: to make unsuitable for passage or progress by obstruction
So sunblock would make passage of the heat or light radiated from the luminous celestial body around which the earth and other planets revolve, from which they receive heat and light, and which has a mean distance from earth of 93,000,000 miles (150,000,000 kilometers), a linear diameter of 864,000 miles (1,390,000 kilometers), a mass 332,000 times greater than earth, and a mean density about one fourth that of earth unsuitable and obstructed.
Suntanning is accomplished by letting the heat or light radiated from the luminous celestial body around which the earth and other planets revolve, from which they receive heat and light, and which has a mean distance from earth of 93,000,000 miles (150,000,000 kilometers), a linear diameter of 864,000 miles (1,390,000 kilometers), a mass 332,000 times greater than earth, and a mean density about one fourth that of earth pass to the skin and the body.
Would sunblock help? You tell me.
(This was presuming you meant SPF25 or 30 sunblock... Use suntan lotion with SPF 4 or 6 rating)