What are the three regions of the atmosphere in order of their relative heights?

The three regions of the atmosphere, in order of their relative heights, are the troposphere, stratosphere, and ionosphere.

The troposphere is the lowest layer of the atmosphere, extending from the Earth's surface up to about 8 to 15 kilometers, depending on the geographical location. It is where all weather events occur and where the majority of the atmosphere's mass resides.

Above the troposphere is the stratosphere, which begins around 10 to 15 kilometers and extends up to about 50 kilometers. The stratosphere contains the ozone layer, which works to absorb and scatter ultraviolet solar radiation, playing a crucial role in protecting life on Earth.

The ionosphere, while not always classified as a distinct layer like the troposphere and stratosphere, extends from about 30 kilometers to around 1,000 kilometers above the Earth's surface. It is characterized by its ionized particles created by solar radiation, which can reflect radio waves and is critical for radio wave propagation.

By placing the troposphere at the bottom, followed by the stratosphere, and then the ionosphere, this answer accurately captures the relationships and relative heights of these atmospheric layers.