1. The Earth's Crust: The crust is primarily composed of oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. While oxygen is the most abundant element by weight, silicon is the most abundant by volume. Oxygen comes in second.
2. The Earth's Atmosphere: The atmosphere is primarily composed of nitrogen (78%) and oxygen (21%). While nitrogen is more abundant by volume, oxygen is the second most abundant element.
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