|from Dan Chure's Land of the Dead|
The griffenfly you see in the image to the right had a two and a half foot wingspan, and for that hefty size we can thank oxygen. The level has varied over geologic time, and was once so high it allowed insects, which breathe less efficiently through tubules rather than lungs, to grow much larger. That was 300 million years ago. There's less oxygen now, hence no more griffenfly; see Dan Chure's, Land of the Dead for more on these fantastic prehistoric insects.
Oxygen is reactive, meaning it likes to strip atoms from surrounding molecules. As such free radicals, oxygen atoms can cause a lot of damage in living tissue. It's probably a good thing the level has gone down. If it were too low, however, it would be that much harder to breathe, as anyone who's been at high altitude can attest to. If not for nature's self-balancing oxygen level, earth would not have quite the diversity of life it does.
Oxygen is key to life in more ways than you might think. It likes to bonds with lots of other atoms, such as hydrogen to make life-essential water. Oxygen atoms bond with themselves and form the diatomic molecules (O2) that we breathe and metabolize energy with. One of oxygen's preferred molecules is trioxide (O3), also called ozone. It resides in the stratosphere and is essential in reducing the amount of harmful ultraviolet light that reaches the planet. Ultraviolet light is a life killer, so those griffenflies, like much of life on earth, would never have evolved.
The diverse ways that patterns in nature come together and allow our planet to teem with life seem miraculous. The earth is nestled in what astronomers call the goldilocks zone; a place in the solar system not too hot and not too cold for liquid water to exist. Jupiter's massive gravity well sucks up many of our solar system's rogue asteroids and comets. In four and a half billion years Earth has experienced about five mass extinction events, and each time life had to start over. If not for Jupiter's protection, many more impacts on our world would have stunted life further. In the center of the earth there is a giant ball of iron spinning inside a vaster liquid ocean of iron. The spin generates the protective magnetic field around the planet. If not for the magnetic field, periodic solar storms would eventually strip away the atmosphere (like happened on poor Mars), and life would be buffeted with deadly radiation.
All of these things allowed for an evolving biosphere and ultimately us.
Some wonder if it is divine providence that creates these seemingly miraculous and interwoven patterns. On the other hand, if not for all of the things that make life on earth possible I wouldn't be wondering about it, would I? It could all be just a numbers game, as according to the most current data there are likely billions of planets just in our galaxy.
As a science fiction writer, I like to think that there are many other worlds that also got life lucky. We are searching...