Here's why:
* First Radio Transmission: The first intentional radio transmission occurred in 1895 by Guglielmo Marconi. However, these signals were weak and short-range.
* Broadcasting Begins: Radio broadcasting started in the early 1920s, with powerful stations transmitting signals over longer distances.
* The "Sphere of Influence": Radio waves travel at the speed of light. So, the signals from Earth's first powerful radio stations have created a sphere of influence around Earth with a radius of 100 light-years.
Therefore, any alien civilization within 100 light-years of Earth could potentially pick up our radio signals.
