AICE Environmental Management Practice Exam 2026 - Complete Preparation Guide

The main gases in the Earth's atmosphere are nitrogen, oxygen, argon, and small amounts of other gases. Nitrogen is the most abundant gas, making up about 78% of the atmosphere, while oxygen accounts for around 21%. Argon is present in trace amounts, approximately 0.93%.

Helium, on the other hand, is not considered one of the main gases in the atmosphere. It exists in very minimal quantities, primarily as a result of radioactive decay and other natural processes, and does not play a significant role in the atmospheric composition or in supporting life on Earth. This distinction of helium being present in negligible amounts compared to the other gases confirms that it is the one that is NOT a main gas in the atmosphere. Understanding this composition is crucial in environmental science, as it helps explain various atmospheric processes and the behavior of other gases.