“The little things are infinitely the most important.” ~ Irish-Scots novelist and physician Arthur Conan Doyle
For nearly 3 billion years, life on Earth kept to tiny single cells. These productive inhabitants were prokaryotes, of 2 main varieties: bacteria and archaea.
In their initial eon, archaea dabbled in most every lifestyle, from eating photons to consuming chemical compounds. The phototropism of archaea was much simpler and direct than photosynthesis, which is a complex quantum process. Various archaea were autotrophic, heterotrophic, or saprotrophic.
Meanwhile, bacteria made a living chewing rocks: unlocking energy from sulfur, nitrogen, iron, and hydrogen. This created sediment that acted as a geologically viscous lubricant, which was instrumental in generating tectonic plate subduction. By this, bacteria facilitated the rise of continents.
Cyanobacteria arose by deriving energy from fermentation, which does not require oxygen. By 3.5 bya, cyanobacteria had acquired the quantum trick of photosynthesis: microscopic reactors, capturing fleeting photons to convert carbon dioxide and water into the universal organic currency for energy: the sugary molecule ATP.
“During the first half of Earth’s history, the majority of life forms were probably capable of photosynthesis.” ~ Columbian biologist Tanai Cardona
Thus chlorophyll was born. It literally changed the world. Animal life on Earth was made possible by the byproduct of photosynthetic bacteria: oxygen.
At first, oxygen was poisonous to life. But organisms adapted and evolved to appreciate the accessible energy that atmospheric oxygen offered.
Oxygenating the atmosphere altered every form of life. Even prodigal oxygen producers had to adapt to their own success.
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Through exquisite adaptation, microbes perfected metabolism to near the optimality afforded by physical chemistry, with the slight trade-off of being able to adjust to alternative nutritional conditions. This efficiency goes a long way in explaining the diversity and staying power of microbes.
Viruses descended from bacteria ~4 billion years ago, slimming down to live vampirishly. But they kept their wits about them. Viral exuberance for communion with others is positively infectious.