Carbon Dioxide - An Essential Ingredient of Life

Life on Earth formed a staggering 3.6 billion years ago. Conditions back then would have been pretty inhospitable to anything composed of more than just a few cells. In fact, that's so long ago that the crust had barely formed, asteroids were still pelting the Earth at an alarming rate and the atmosphere probably had upwards of 250 times more CO₂ than it does today.