The Paradoxical Element That Gives Life and Takes It Away
We breathe it without thought, approximately 20,000 times each day, yet oxygen holds a deeper story than mere sustenance. This invisible gas, making up 21% of our atmosphere, is the protagonist of an epic saga spanning billions of years—a tale of catastrophic extinctions, evolutionary leaps, and the fundamental processes that dictate how we age and die.
Nick Lane's Oxygen: The Molecule that Made the World unravels this extraordinary paradox: how could the same element that enables complex life also act as a potent poison that ultimately contributes to our demise? This journey explores everything from dragonflies with seagull-sized wingspans to the hidden reasons we grow old, revealing how oxygen fundamentally shaped our world and continues to influence our future.
Around 2.7 billion years ago, cyanobacteria began releasing oxygen through photosynthesis, causing Earth's first mass extinction 8 . For anaerobic life, this new atmospheric component was disastrously toxic.
As oxygen levels rose, it reacted with atmospheric methane, potentially triggering global cooling while permanently changing planetary chemistry 8 .
Life evolved to harness oxygen's reactivity through aerobic metabolism. Oxygen's high redox potential made it an ideal terminal electron acceptor, allowing more efficient energy generation than anaerobic processes 8 .
This metabolic innovation paved the way for complex multicellular life, enabling evolutionary experiments in complexity that were previously impossible 1 .
As cells metabolize oxygen, they generate reactive oxygen species (free radicals) that can damage proteins, lipids, and DNA 1 .
This damage accumulation is thought to be a primary contributor to aging and age-related diseases. Lane examines why organisms with higher metabolic rates don't necessarily age faster, challenging simplistic interpretations of the free-radical theory 1 .
Discovering "Dephlogisticated Air"
Used a 12-inch-wide glass "burning lens" to focus sunlight onto mercuric oxide contained in an inverted glass vessel placed in mercury 6 .
The mercury pool created a seal preventing outside air contamination while allowing gas collection.
When heated, mercuric oxide decomposed: 2HgO(s) + heat → 2Hg(l) + O₂(g)
Tested the gas with flames and living organisms to determine its properties 6 .
He found the gas was "five or six times as good as common air." In succeeding tests, it caused a flame to burn intensely and kept a mouse alive about four times as long as a similar quantity of air.
He noted the personal experience of breathing this new gas: "The feeling of it in my lungs," Priestley wrote, "was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards" 6 .
Despite his groundbreaking discovery, Priestley remained wedded to the prevailing phlogiston theory, calling his discovery "dephlogisticated air" 6 . It would take Antoine Lavoisier's systematic work to correctly interpret oxygen's role in combustion and rename the element 5 6 .
| Observation | Result | Modern Interpretation |
|---|---|---|
| Flame test | Burned more intensely and brightly | Oxygen supports combustion more effectively than air (which is only ~21% oxygen) |
| Mouse viability | Survived 4x longer than in ordinary air | Oxygen essential for efficient cellular respiration |
| Personal inhalation | "Breast felt peculiarly light and easy" | Subjective experience of pure oxygen breathing |
| Gas production | From heating mercuric oxide | Mercuric oxide decomposes to mercury and oxygen gas |
An Evolutionary Timeline
The history of oxygen on Earth is marked by dramatic fluctuations that directly influenced the evolution of life. By examining key periods, we can see how oxygen levels shaped the development of everything from single-celled organisms to the giant creatures of prehistoric times.
| Time Period | Oxygen Level (Approx.) | Biological Impact |
|---|---|---|
| Pre-2.4 billion years ago | <1% | Anaerobic life dominates; oxygen virtually absent from atmosphere |
| Great Oxidation Event (2.4-2.1 bya) | Rising to ~1-5% | First mass extinction of anaerobic life; beginnings of aerobic metabolism |
| Carboniferous (300 mya) | ~35% | Giant insects (dragonflies with 1m wingspans); global firestorms possible |
| Present Day | 20.95% | Current balance supporting diverse life forms while causing gradual oxidative damage |
Key Research Reagents in Oxygen Science
Understanding oxygen's role in biological systems requires specialized reagents and materials. This toolkit highlights essential components used in studying oxygen's effects on life processes, from historical experiments to contemporary research.
Function: Thermal decomposition produces oxygen
Application: Laboratory oxygen generation, catalyzed by manganese dioxide 9
Function: Antioxidant enzyme neutralizing superoxide radicals
Application: Studying oxidative stress and cellular damage 8
Function: Enzyme decomposing hydrogen peroxide
Application: Research on oxidative stress management in cells 8
Function: Protected amino acids for peptide synthesis
Application: Studying protein structure and oxidative damage 7
Oxygen remains a molecule of profound contradictions—both essential and dangerous, creative and destructive. As Nick Lane masterfully illustrates in Oxygen: The Molecule that Made the World, understanding this elemental paradox helps explain not only life's ancient history but also our own biological future.
From Priestley's first experiments with "dephlogisticated air" to modern research on aging and disease, oxygen continues to challenge and fascinate scientists across disciplines.
The very air we breathe connects us to cyanobacteria that transformed a planet, prehistoric dragonflies that soared through oxygen-rich skies, and the fundamental biochemical trade-offs that dictate our health and lifespan. As research continues, particularly in understanding how different organisms manage oxidative stress, we may uncover new insights into aging, disease, and perhaps even ways to extend human healthspan—all by better understanding the molecule that made our world.