Radio propagation that rely on reflection (actually refraction) of radio waves from the ionosphere. The ionosphere is a region of the atmosphere from about that contains layers of charged particles (ions) which can refract a radio wave back toward the Earth. A radio wave directed at an angle into the sky can be reflected back to Earth beyond the horizon by these layers, allowing long distance radio transmission. The F2 layer is the most important ionospheric layer for long-distance, multiple-hop HF propagation, though F1, E, and D-layers also play significant roles. The D-layer, when present during sunlight periods, causes significant amount of
Atmospheric escape brighter than it is now, making it hot enough for Earth to lose enough hydrogen to space to cause it to lose all of its water (See Future of Earth#Loss of oceans). Atmospheric escape Atmospheric escape is the loss of planetary atmospheric gases to outer space. A number of different mechanisms can be responsible for atmospheric escape, operating at different time scales; the most prominent is Jeans Escape, named after British astronomer Sir James Jeans, who described the process of atmospheric loss to the molecular kinetic energy. The relative importance of each loss process is a function of the planet's