Imagine a world where scorpions were as large as dogs, and dragonflies had wingspans wider than a human arm. This wasn't the plot of a sci-fi film—it was Earth's reality 300 million years ago, during the Carboniferous period. In his book The Story of CO₂, science journalist Peter Brannen explores how extreme carbon dioxide levels shaped our planet's ancient ecosystems.
The Age of Giant Arthropods
Brannen reveals that atmospheric CO₂ concentrations during the Carboniferous were nearly 15 times higher than pre-industrial levels. This supercharged greenhouse effect created a world where oxygen levels reached 35% (compared to today's 21%), allowing arthropods to grow to monstrous proportions.
Why Size Mattered
The book explains three key factors behind these prehistoric giants:
- Oxygen abundance: Higher O₂ levels enabled more efficient respiration in arthropods' primitive respiratory systems
- Warmer climate: Elevated CO₂ created tropical conditions across the globe
- Evolutionary advantage: Larger size provided protection against newly evolving vertebrate predators
Modern Parallels and Warnings
While we're unlikely to see dog-sized scorpions return, Brannen draws sobering parallels between ancient CO₂ spikes and today's climate crisis. Current CO₂ levels at 420 ppm—the highest in 3 million years—are changing ecosystems at unprecedented rates.
The book serves as both a fascinating deep dive into Earth's history and a timely reminder of how profoundly atmospheric composition shapes life on our planet.
