Rain occurs through the water cycle of evaporation and condensation. Water evaporates from Earth's surface due to heat from the sun, rises into the atmosphere as vapor, cools and condenses into liquid water droplets, and falls as precipitation like rain or snow. Some rain evaporates before reaching the ground, seen as virga in dry regions. Cell phones work by transmitting radio signals to cellular towers connected to switching stations and wired telephone networks to connect calls between mobile and other phones. Earthquakes happen when built-up pressure causes rocks underground to break suddenly along faults, releasing energy as seismic waves that shake the ground.