Q: What is the most abundant element...

Q: What is the most abundant element on Earth?

A: Oxygen, which composes about 49.5% of the total mass of the Earth’s crust, waters and atmosphere, according to the textbook “Modern Chemistry.” Silicon is second at 28%. Aluminum is a distant third, at only 8%. Compounds of silicon and oxygen make up 87% of the materials in the Earth’s crust.

Beyond the Earth, however, the situation is quite different. Hydrogen, the lightest element, makes up about 75% of the mass of the universe, accounting for 90% of all atoms. Most of the rest are helium.