Oxygen May 2026

Earth was not always the "blue marble" we know today. For the first half of its 4.5-billion-year history, the atmosphere was almost entirely devoid of free oxygen. Approximately 2.4 to 2.1 billion years ago, a pivotal biological innovation changed everything: .

While we often focus on the 21% of oxygen in our atmosphere, the vast majority of Earth's oxygen is actually hidden beneath our feet. The origin of atmospheric oxygen on Earth - PNAS oxygen

). However, when cooled to extreme temperatures, it transforms into a striking pale blue liquid or solid. Earth was not always the "blue marble" we know today

Oxygen is much more than just the air we breathe; it is a foundational pillar of terrestrial existence, a highly reactive chemical powerhouse, and a critical tool in modern medicine and industry. From its absence in Earth’s primordial atmosphere to its current role as a life-sustaining gas, oxygen's story is one of radical transformation. While we often focus on the 21% of

Early microorganisms, precursors to modern cyanobacteria, began using sunlight to split water molecules, releasing oxygen as a byproduct. This led to the Great Oxidation Event (GOE) , an environmental shift that paved the way for complex multicellular life and the evolution of aerobic respiration.

Oxygen is a nonmetal element with the symbol and atomic number 8 . In its most common form at room temperature, it exists as a colorless, odorless, and tasteless diatomic gas ( O2cap O sub 2