A satellite photograph of Earth. Oxygen is a major constituent of the planet’s mass and is the third most abundant element in the universe after hydrogen and helium.

A satellite photograph of Earth. Oxygen is a major constituent of the planet’s mass and is the third most abundant element in the universe after hydrogen and helium.

A satellite photograph of Earth. Oxygen is a major constituent of the planet’s mass and is the third most abundant element in the universe after hydrogen and helium.