Why does the decimal system need a decimal point for fractions?

The decimal system is a positional numeral system that relies on the base of 10 to determine the value of digits based on their position.1

The decimal point is essential because it serves as a separator that distinguishes whole number place values from fractional place values, which represent negative powers of 10. In this positional scheme, digits to the left of the point represent increasing powers of 10 (${10}^0,{10}^1,{10}^2$, etc.), while digits to the right represent decreasing powers of 10 (${10}^{-1},{10}^{-2}$, etc.).1

Without this marker, it would be impossible to distinguish between a whole number and a decimal fraction or to identify the specific power of 10 intended for the fractional digits. For example, in the number 543.21, the decimal point clarifies that the 2 and 1 represent tenths and hundredths, respectively, rather than whole units.12