Review of Oxygen - The Molecule that made the World

Written by: Tushar Sharma

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These are my rough notes while reading this book

Nitrates in food are used as preservatives, especially in processed meats like bacon and sausages. When these foods are deep-fried or cooked at high temperatures, the nitrates can react to form nitrosamines, compounds known to be carcinogenic.

The saying "diamonds are forever" comes with a caveat. Diamonds are forever only in the absence of oxygen. In an oxygen-rich environment and at extremely high temperatures, diamonds can burn and convert to carbon dioxide (CO₂).

Lavoisier, the French chemist, played a crucial role in our understanding of oxygen. He demonstrated that combustion (burning) and respiration (breathing) are fundamentally the same process—both involve the reaction of oxygen with other substances to release energy. He was executed by guillotine during the French Revolution, despite his immense contributions to science.

Potassium nitrate (KNO₃), also known as saltpeter, is used in fertilizers and gunpowder. When mixed with acids, it can release nitric acid, historically called aqua fortis or “acid of nitre.” Combined with hydrochloric acid, it forms aqua regia, one of the few substances capable of dissolving gold.

Does oxygen accelerate aging? Oxygen is essential for life, but it’s also inherently damaging. Reactive oxygen species (ROS)—byproducts of normal metabolism—can damage DNA, proteins, and cell membranes. This oxidative stress is a key factor in aging and many degenerative diseases. Even moderate increases in oxygen concentration can harm tissues. For instance, breathing pure oxygen for extended periods causes lung inflammation and other toxic effects. Experiments have shown that exposure to air containing just 33% oxygen (instead of the normal 21%) can cause serious inflammation over time.

However, oxygen is also life-saving in controlled medical use. People with pneumonia or respiratory distress benefit from supplemental oxygen because it increases the amount of oxygen available to damaged lungs. Likewise, people living at high altitudes (where oxygen levels are lower) often develop physiological adaptations like higher red blood cell counts to compensate for reduced oxygen availability.

In the early days of diving, some rebreathers used pure oxygen. But divers soon learned that breathing pure oxygen under pressure causes oxygen toxicity, leading to convulsions or even death underwater. Today, scuba divers use carefully balanced gas mixtures:

Air (21% O₂, 78% N₂) for most recreational dives.
Nitrox (32–36% O₂) for extended bottom times at moderate depths.
Trimix or Heliox (oxygen diluted with helium or nitrogen) for deep dives to avoid both nitrogen narcosis and oxygen toxicity.
Pure oxygen is still used, but only at very shallow depths or during decompression stops.

The first great mass extinction on Earth was ironically caused by oxygen. Around 2.4 billion years ago, during the Great Oxygenation Event, photosynthetic cyanobacteria began releasing large amounts of oxygen into the atmosphere. For most existing life—which was anaerobic (thrived without oxygen)—this new gas was toxic. The buildup of oxygen wiped out much of early microbial life and dramatically changed Earth’s chemistry, paving the way for the evolution of more complex, aerobic organisms.