If all animals vanished, most bacteria would still live on, but if all bacteria disappeared, we would die quickly.
Cells are the atoms of life, and life is what cells do.
— Franklin M. Harold, In Search of Cell History, p. 2
In the above post we were tracing our heritage back to chimps and gorillas. Is it a bridge too far to take your heritage back to a rock? Okay perhaps, but strange as it may seem, there are similarities between you and a rock…. A rock is made of oxygen, carbon. nitrogen, iron and calcium, and so are you. What is it that clearly occupies this middle ground between geology and biology, between the organic and the inorganic? Minerals! If you break open a rock what do you find? Minerals. What is your body made of? Minerals. From shells to teeth and bones, mineralogy contributes to life while life contributes to mineralogy. An active biosphere is one that is constantly demonstrating give and take between its participants, and mineralogy is the overlapping link between the animate and inanimate. Geochemistry demonstrably gives rise to biochemistry.
Nothing seems more lifeless than a rock. It’s inanimate. It’s the antithesis of a living thing. But we are beginning to realize that rocks played an absolutely fundamental role in the origin of life…. This is a very new set of understandings, and the more we look, the more we see that life depends on rocks, rocks depend on life. And this has been going on for four billion years.
— Robert Hazen, PBS, Nova: Life’s Rocky Start, 2016
Life gathered out of the materials that were readily available — and that is to say that life arose out of the most common elements on the earth. Simply, lemons made lemonade. As the Miller-Urey experiment showed back in the 1950s, the compounds of life could have arisen very quickly on early earth, and as many meteorites demonstrate, simple amino acids and organic compounds are found in abundance within any random rock floating in space. The old school of thought of these compounds organizing into life from shallow ponds has been challenged in recent decades by the idea that deep sea hydrothermal vents (discovered in the 1970s) might have been more likely catalysts, and that itself has given way to the discovery of underwater alkaline vents, the slightly more hospitable variant of their hot cousins that were found in 2000. The unique property that water possesses is its ability to dissolve and mix compounds. Water is a soup of life… a soluble of something, anything or everything. If “Water” were to be added to Rock, Scissors and Paper the game would be over because Water would ultimately win every time. Water wins the game of life. Water is a kind of cheat code that wins everything.
Over time water dissolves rock, and in so doing it releases gases that alter the PH level of the body of water. At its most fundamental cellular level, life is essentially born out of the same simple processes that power a battery — alkalinity (a proton deficiency) vs. acidity (a proton surplus); that is to say, harnessing energy from an imbalance of protons (a proton flow from a reservoir of too many protons to a reservoir of too few).
The oldest fossils of life go back some 3.5 billion years, though there is a strong suggestion and signature of life at 3.8, but the general consensus is that life might date back to 4 billion years or longer. As long as there is liquid water, there is a possibility of life, and as zircons — the hardy survivors or early earth — clearly indicate, there were oceans in place on earth by 4.3 billion years ago. So at some point between 4.3 billion years ago and 3.8 billion years ago, there emerged a first cell, and every cell in your body is a direct descendant of that cell.
You have parents, you have grandparents. You have great-grandparents. But this goes, like way, WAY back. Like a person, no cell is created out of the blue, it is created from the cell that came before it. “Omnis cellula e cellula.” Every cell in your body is a testament to and legacy of 4 billion years of life on earth. Each and every cell that makes your body is the latest link in an unbroken chain that dates back to one-third of the age of the universe. And so does every cell in the grass of your lawn. And your pet. As far as we can tell, all life of earth emerged from the same tree of life. Plants and animals share a same common ancestry; only unlike chimps — from whom we humans diverged about 6 million years ago — plants and animals (or what would much later become plants and animals) diverged about 1.6 BILLION years ago, while both existed only at the microbial stage. Really, any understanding of life on the scale of deep time starts with two basic facts (and the one factor that altered them both). Let’s spend a moment or two to consider the first, because once that first cell arose, life, well… really… took… its… time.
- The mind-blowing majority of the history of life on earth was microbial. Life on earth began some 4 billion years ago, and for 85% of those 4 billion years the most advanced life on the planet was single-celled bacteria, Prokaryotes, and later Eukaryotes — our ancient and primitive single-celled ancestors.
Life appeared on Earth within a few hundred million years, but for billions of years it was restricted to single celled organisms.
In the 1970s our current scientific classification of the Three Domains of Life was established: Bacteria and Archaea — the two Prokaryotic (and primary) domains, which have evolved very little in 4 billion years — and Eukarya, a minor offshoot whose cells seem more closely related to Archaea than Bacteria, though conversely the mitochondria within each cell seems more closely related to Bacteria than Archaea.
You are an Eukaryote. Eukarya is the domain that encompasses all complex life — all people, all plants, all animals, any and all life that is big enough for you to see (and some you can’t) comes from this small, modest and much-mutated branch. We’re an extended footnote in a thousand-page book. Eukarya represents a fraction of a fraction of the life on earth, but it represents all the life that can be seen without a microscope. Eyes, ears, limbs, backbones, hair, scales and toes — BRAINS, for that matter — bacteria and single-celled life that dominates the biosphere have none of these things; these are tools and inventions only made possible with the joining of cells into complex structures. Eukaryotes have the freedom to link together cells like a kid tossing together Legos. With Eukarya, complexity built upon complexity… in contrast to bacteria, which has spent 4 billion years essentially in a flatline.
The consensus today is that Eukarya represents an unlikely merging of the two Prokaryotic types that occurred only once. Anyone of a certain age will remember those old Reeses Peanut Butter Cups commercials, speculating about the origins of the candy as two people walking on the street collide and exclaim, “Hey, you got chocolate in my peanut butter!” “Hey, you got peanut butter in my chocolate!” Pause. Taste. Both cry out, “YUM!” The analog here is that the mitochondria is that peanut butter that gave an unexpected zing to the chocolate.
According to Wikipedia, “the most accredited theory at present is endosymbiosis… The endosymbiotic hypothesis suggests that mitochondria were originally prokaryotic cells, capable of implementing oxidative mechanisms that were not possible for eukaryotic cells; they became endosymbionts living inside the eukaryote.” (https://en.wikipedia.org/wiki/Mitochondrion) In a symbiotic relationship, mitochondria ended up jettisoning much of its own genes, in the process becoming a power source for the eukaryotic cell. In the words of Nick Lane, with mitochondria — the “batteries” that power each eukaryotic cell — “Eukaryotes have 100,000 times more energy per gene than bacteria, which allows them to support far larger and more genomes and make far more proteins from each gene.” (https://www.youtube.com/watch?v=PhPrirmk8F4)
Given how early life on earth began, it seems a strong argument that simple life is an easy threshold to cross… considering the fact that Eukaryotic life seems to have emerged only ONCE in 4 BILLION YEARS may suggest that this may be the truly “narrow needle to thread.” Achieving complexity, then, is akin to a lottery, that played endlessly and relentlessly over two and-a-half billion years, eventually resulted in winning numbers. The sheer immensity of time eventually gives rise to the unlikely. Once in 4 billion years is a very lucky stroke, but if time is on an immense enough scale all odds eventually fall away.
Really, one factor was responsible for the possibility of complex life, and that factor was oxygen. It is only in this last 15% of life’s history on earth (600 million years) that significant multicellular life has arisen, and a freakish abundance of oxygen seems to have produced the fuel for driving complexity.
Now, if it seems sobering that 85% of life’s history was simple, unchanging and unicellular, here’s the second fact to consider…