GED Science Practice 2025 - Free GED Science Practice Questions and Study Guide

The ionosphere is indeed an outer region of the Earth's atmosphere, situated roughly between 30 miles (48 kilometers) and 600 miles (1,000 kilometers) above the Earth's surface. This layer is characterized by the presence of ionized particles, which are created when the sun's ultraviolet and X-ray radiation interacts with atmospheric gases.

One of the key functions of the ionosphere is its role in radio wave propagation. The ionized particles can reflect and refract radio waves, allowing them to travel over long distances beyond the horizon, which is particularly useful for communication. This property is why the ionosphere is important for both commercial and amateur radio communications, as well as for determining the position of satellites and other spacecraft.

In contrast, the innermost layer of the atmosphere refers to regions like the troposphere, which is where weather events occur. Being below the Earth's crust pertains to geological layers, such as the mantle and core, which are entirely different from atmospheric layers. Lastly, the Earth’s core is a solid inner layer surrounded by a liquid outer layer that is crucial for the planet’s magnetic field but is not related to the ionosphere.