TeXes Science Practice Test

Which factor contributed to the early atmosphere of the Earth breaking down gases?

1. Geothermal activity

2. Solar winds

3. Sun's ultraviolet radiation

4. Asteroid impacts

The correct answer is: Sun's ultraviolet radiation

The early atmosphere of the Earth was primarily composed of gases such as hydrogen and helium, which were later influenced by a variety of factors. The primary reason that the Sun's ultraviolet radiation significantly contributed to the breakdown of gases in this atmosphere lies in its ability to provide high-energy photons. As the early Earth was bombarded by high levels of ultraviolet radiation due to a weak magnetic field and a lack of an ozone layer, this radiation caused photodissociation. Photodissociation is a process where molecules break apart into their constituent atoms under the influence of UV radiation. For instance, the intense ultraviolet light could break down water vapor into hydrogen and oxygen. This splitting of molecules contributed to a change in the atmospheric composition, paving the way for the development of a more complex atmosphere that would later support life. While geothermal activity, solar winds, and asteroid impacts may also have played a role in shaping the early Earth's environment, they did not directly break down atmospheric gases in the manner that ultraviolet radiation did. Therefore, recognizing the role of the Sun's ultraviolet radiation is crucial in understanding the evolution of the Earth's atmosphere during its formative years.