The F1 layer, also known as the first layer of the F1 region in the Earth's atmosphere, is primarily composed of ionized particles. This layer plays a crucial role in radio wave propagation, as it reflects certain frequencies back to the Earth's surface, enabling long-distance communication. The F1 layer is part of the ionosphere, which is situated approximately 150 to 1,000 kilometers above the Earth. It is influenced by solar activity, with its density and height varying throughout the day and across seasons, affecting various technologies such as GPS and satellite communications.