First Life

What was the first living organism on Planet Earth?

Hmm… that depends. Cue the queue of questions. What do you mean by living? Why would you assume there must be a singular first? What’s your definition of organism? Isn’t Planet Earth itself an organism?

Perhaps you’ve heard of LUCA, the Last Common Universal Ancestor. Using phylogenetics, scientists have attempted a top-down approach to elucidate the bare minimum crucial functionality of the organism at the root of the Tree of Life. Yes, I called it an organism – because the entity in question shows some degree of modularity in its function with separate parts playing separate roles. Where was LUCA’s Garden of Eden? The most popular suggestions right now are hydrothermal vents, for a variety of reasons. The acidic vents seem hellish; the milder alkaline vents might not be so bad.

There might not have been one LUCA with a specific genetic code. Instead, a community of similar-functionality organisms may have co-evolved thanks to horizontal gene transfer, maintaining adaptability with variability. But here I’ve assumed that an individual is an enclosed cell-like entity; I’ve defined a (membranous) boundary to separate one individual from another. Maybe the original question should be: What was the first ecological community on Planet Earth? After all, can an individual organism be alive independent of its environment? How would it exchange energy and molecular matter to maintain itself away from equilibrium death? What is living anyway?

The thorny issue is related to how we define life versus non-life. There is no universally agreed-upon definition, perhaps for good reason. Maybe the binary boundary is not so clear cut. Multicellular eukaryotes such as ourselves might be considered confederacies of multitudes of organisms. Or perhaps we are just one big super-organism, Gaia, and those boundaries are artificial. I’m not so sure about that last one, that is, I think the boundaries are interesting in theory and certainly seem useful in practice. But where do they come from and why do we have them?

In the physical realm (acknowledging my bias as a chemist), one might first think of atoms as fundamental entities. Atom A is an individual entity. Atom B is a separate individual entity. Atom A has its own boundary, often assumed spherical, as does Atom B. But how did A and B gain their own separate identities? An introductory chemistry class might discuss protons, neutrons and electrons. Atoms are differentiated as different elements based on the number of protons, and their chemistries might be different based on the number of outer electrons.

But where did these sub-atomic particles come from? How did they differentiate from each other? A physicist might say that in the beginning was the high-energy field, and as the universe expanded and cooled, different particles condensed into existence (a sort of phase change) because of certain symmetries. There could have been a zoo’s worth of different particles, but planet Earth uses only a few types including the proton, neutron and electron. These three condensed further into mostly hydrogen, some helium, and a little lithium; and then built up some of the higher elements up to a limit. Go past 83 protons and atomic nuclei are inherently unstable, prone to radioactive decay.

Living things pick out only a few elements to use over and over again: CHNOPS (Why?) and trace amounts of metals. But these few elements lead to a huge diversity of molecules, thousands upon ten thousands. But yet again, living things condense this list into a small number of metabolites and building blocks; and this leads to a diversity of organisms of all shapes and sizes.

There’s a pattern here. It’s like a hotspot gated by a bouncer, there’s a large crowd but only a small subset gets to join the party. Open. Close. Open. Close. With double-sided funnels to facilitate the motion. You might even picture a bow-tie architecture. And perhaps this is how we classify hierarchies of individual entities. The proton. The atom. The molecule. The cell. The organism. The ecosystem. Each has its own boundary conditions. Fuzzy they may be, but this allows us at a practical level to make distinctions between entities. What is life? Perhaps this strange pattern of unity and diversity gives us some clue.