How a simple molecule shaped our world, from the first breath to our final days.
We hardly give it a thought. With every effortless breath, we draw in the invisible gas that sustains us. Oxygen is the essence of life, the fuel for our cells, and a cornerstone of our very planet. But what if we told you that this life-giving molecule was once the worst pollutant the Earth had ever seen? That it triggered global ice ages, mass extinctions, and ultimately, forced life to evolve in a dramatic new direction? This is the incredible story told in Nick Lane's Oxygen: The Molecule that Made the World—a tale of catastrophe, creativity, and the delicate balance that keeps us alive.
For the first half of its existence, Earth was an anaerobic planet—devoid of free oxygen (O₂). Its atmosphere was a suffocating mix of methane, carbon dioxide, and other gases. Life existed, but it was simple, single-celled, and microscopic, thriving in the oxygen-free depths of the oceans.
Then, around 2.4 billion years ago, a revolutionary invention emerged: photosynthesis. Certain bacteria, the ancestors of today's plants and algae, learned to harness sunlight to turn water and CO₂ into food. There was just one world-changing waste product: oxygen.
To the existing lifeforms, oxygen was a deadly poison. It reacted violently with their cellular structures, causing a biochemical meltdown.
The Great Oxygenation Event was the planet's first, and perhaps most severe, mass extinction.
Earth forms with an atmosphere containing no free oxygen
First life appears - anaerobic microbes
Photosynthesis evolves, oxygen begins accumulating
Great Oxygenation Event causes first mass extinction
The key to oxygen's success lies in its incredible reactivity. It's a greedy molecule, eager to rip electrons from other substances. While this makes it destructive, it also makes it an incredibly efficient fuel source.
The breakthrough was the evolution of the mitochondrion—a tiny powerplant inside our cells. Mitochondria perform aerobic respiration, a process that uses oxygen to "burn" food molecules and generate energy.
Aerobic respiration produces 18x more energy than anaerobic respiration
Produced from one glucose molecule without oxygen
Produced from one glucose molecule with oxygen
This energy bonanza provided the power necessary for complex life to evolve. Multi-cellular organisms, large predators, and eventually, us—all owe our existence to that moment life tamed oxygen's fiery nature.
One of the most compelling applications of oxygen science is in solving history's greatest whodunnits. The End-Permian extinction, 252 million years ago, was the closest life ever came to being completely wiped out. A staggering 96% of marine species and 70% of terrestrial vertebrate species vanished. For decades, the cause was a mystery. Was it an asteroid? Volcanic activity? A crucial experiment shed new light on this catastrophe.
The extinction was caused by a collapse in oceanic oxygen levels (anoxia), triggered by massive volcanic eruptions in Siberia.
| Sample Layer (Age) | δC-13 Value (‰) | Interpretation |
|---|---|---|
| Late Permian (Before Extinction) | +4.0 | Normal biological activity |
| Extinction Boundary | -2.0 | Massive injection of CO₂ |
| Early Triassic (After Extinction) | +1.5 | Struggling, low-diversity ecosystems |
| Evidence Type | Finding in P-T Sediments | Indicates |
|---|---|---|
| Uranium Isotopes (δU-238) | Sharp negative excursion | Severe global anoxia |
| Pyrite Framboid Abundance | High concentration & small size | Prolonged, toxic seafloor conditions |
| Fossil Record | Disappearance of burrowing organisms | Lack of oxygen in seafloor sediments |
The End-Permian extinction was the most severe in Earth's history
Oxygen's story doesn't end with giving us energy. Its reactive nature is a constant threat. During energy production, mitochondria leak free radicals (Reactive Oxygen Species or ROS)—unstable oxygen molecules that damage DNA, proteins, and fats.
This is the oxidative stress theory of aging. We essentially rust from the inside out. Our bodies have a sophisticated army of antioxidants to fight this damage, but over time, the accumulated wear and tear contributes to aging and age-related diseases like cancer, Alzheimer's, and heart disease.
The very molecule that gave us the energy for complex life also writes the expiration date on our bodies.
The human body has developed multiple defense mechanisms against oxidative stress:
The story of oxygen is a humbling reminder of our planet's dynamic history and our own fragile place within it. It is not simply the "gas of life." It is a molecule of immense power—a planet-shaping force, a driver of evolution, a historical record-keeper, and a necessary poison. From its toxic beginnings to its central role in our energy and our health, oxygen truly is, as Nick Lane argues, the molecule that made our world. The next time you take a deep breath, remember you are drawing in a billion years of history, a paradox of creation and destruction, and the very fire that powers your existence.
Since oxygen first appeared
Aerobic vs anaerobic energy production
Wiped out in Permian extinction
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