"Life-friendly molecules" is the cute phrase of the day. My personal favorites are O2 and CH3-CH2-OH.

Agreed. Single cell life evolved around 4-3.5 billion years ago when the early earth's atmosphere was devoid of appreciable levels of oxygen. Many of these early life forms died out in the first mass extinction brought on by the evolution of cyanobacteria and the subsequent great oxygenation event of our planet about 2.5 billion years ago. It is always fascinating to remember that the introduction of such a reactive element (oxygen) to our planet in the form of O2 resulted in evolutionary opportunities for energy capture in biological systems by oxidation of food (sugars, amino acids, fats) to generate ATP and GTP. Processes that we humans carry out with respiration. Increased available oxygen dissolved in world oceans and in the atmosphere also lead to an extensive diversification in the minerals present on earth. So the rise of oxygen producing life forms actually terraformed earth to the conditions we see as 'normal' today. We live by exploiting oxidation in a world crafted by oxygen generating life. You can still see cyanobacterial stromatolites in Shark Bay, Australia and imagine a similar scene 2 billion years ago.