Oxygen

Oxygen helps you understand the biology of our evolution by taking a close look at the molecule that can make and break all life and how it’s shaped the rise of animals, plants and humans, as well as why it might be the key to ending aging.

Most of the organisms we know and interact with today are multi-cellular. Animals, humans, and most plants on earth have many different types of cells. But life didn’t start that way.

Around 500 million years ago, most of earth’s organisms were uni-cellular – they only had one type of cell. For those organisms, oxygen was a death threat. They didn’t have any anti-oxidants, so when exposed to O2, it’d steal their cells’ electrons and make them disintegrate (kinda like this).

During that time, the Cambrian Explosion, plants were the only remaining survivors of a long ice age. Since they photosynthesized a lot of oxygen to survived, it amassed in the atmosphere and oceans.

All of the single-cell organisms in the water tried to escape from all the oxygen around them, but with so much oxygen everywhere, they had no choice but to huddle up together and form a single mass. Eventually, many single-cell organisms integrated into the first multi-cellular organisms, which led to the start of evolution as we know it.

Ironic, huh? More oxygen, more organisms trying to escape it, and the result? Multi-cellular organisms, which thrive on oxygen.

Because the floods from the ice age then washed out tons of minerals and nutrients from the earth, these new organisms lived in an evolutionary utopia, and that’s why they developed so fast (hence the term “explosion”).

In fact, animals were on a meteoric rise in terms of sophistication and size after that point. Fast forward 200 million years from what we just talked about (that puts us 300 million years ago) and if you had walked around outside back then you’d have seen dragonflies with wings spanning 2 feet (65 cm), scorpions of over 3 feet in length (1m) or mayflies with huge wings.

The reason these animals could grow to such huge sizes is that the atmospheric oxygen level was about 35% (as opposed to 21% today).

This not only meant more oxygen for breathing and cell growth, but also that moving around was a lot easier, thanks to the oxygen-rich environment. For example, huge dragonflies wouldn’t be able to fly in today’s 21%-oxygen air, but could generate enough lift for taking off when oxygen levels were that high.

Similarly, air provided less resistance against moving objects at those oxygen levels, so scorpions and other land animals could run and move faster, thus getting an advantage when hunting for food.