Reflecting back, he raised a very important consideration. Obviously we’re on Earth, not Pluto, because this is where life occurred. But the conditions on Earth were good – the moderate temperatures, the stable axis of rotation caused by the moon, which was itself a lucky accident ... the right mix of gasses and organic compound. But how did life occur? That's what I think about in this entry, after doing a little reading.
False starts aside, after the first cellular organism divided into two living things it's easy to understand what happened next. It continued dividing. The first living thing probably found a lot of food lying around and there clearly were no predators.A single bacterium, I've read, if provided optimal conditions, could become a mass the size of the Earth in 9 days, the size of our galaxy in 15 days, or the size of the visible universe in 20 days. Early conditions on Earth certiainly weren't that wonderful, to say the least, but once life got started it very well may have been off and running. Connecting the dots from then to now is not only relatively easy, it's also very fun!
But how did life happen in the first place? There is always spontaneous generation, or a spark of life from God, if you want to skip over it altogether. There's no evidence for either. But there are several realistic ideas -- one proposal is another sort of non-solution called exogenesis which just means life here was seeded from elsewhere. In a more bold version, panspermia, the universe is teeming with simple life,and it continues to rain down upon us. Since conditions elsewhere are largely unknown, if it happened there we may never understand how it did. There are those who argue that it was divinely created by a divine being, or it always existed with no start or end. But they can talk amongst themselves, as they do. True panspermians point out the vastness of the universe and the fact that interstellar dust contains many of the building blocks of life, if not dessicated bacterium themselves, though evidence for the latter is thin.
The more popular explanation is that life began on Earth. Life must do two things: survive and replicate, and there's a disagreement over which came first. One of the more fanciful replication-first ideas is called "clay theory;" it suggests that silicate crystals were the first replicants, spreading by wind or in solution, causing a chemical reaction now and then which begat more bits of themselves. If these particles spread or copied more efficiently when coated with organic film, as some minerals are coated today, natural selection could have taken these wrapped bits (more likely, just the wrappings) a few more incremental steps to create a pseudo-cell ... and there you go.
A more popular theory is that life rose out of the "primordial soup," maybe in shallow waters where organic matter could accumulate, maybe jolted by lightning or stimulated by sunlight. Or in volcanos, or deeper underground. After all, little protein-like spheres can be created today with heated lava bits and amino acids in a laboratory setting. Or life could have started in freezing areas; there's some evidence for this as well. The day/night cycle might have caused a pulsating temperature which stimulated interesting reactions. The shoreline might have provided a linear zone of accumulation, and radioactive minerals may have accumulated there. Bubbles provide another haven. Whichever direction it came from, early life likely, at some point, involved RNA, the short assistants to today's DNA.
Maybe the most popular and well developed position is that life happened first in the deep ocean at the hot alkaline vents which still spew. It is said that these pH and heat gradients -- where hydrogen-rich fluids encounter carbon-dioxide rich fluids -- provide for a series of interesting interactions I've had detailed by an expert and won't pretend to understand in full. Tiny crevices in the iron-sulfer formations there may have served as the first pseudo-cells, isolating miniscule areas in which interesting things could happen in concentration. Eventually these units began to replicate, and then mutate, then they developed their own lipid membranes and became mobile. They were probably simple and vulnerable, but were being pumped out in large quantities.
And all this probably took just 500,000,000 years.
I'm reminded of Siddhartha Mukarjee's extraordinary book The Emperor of All Maladies: A biography of cancer. Cancer is a disease, not a life form, but it shares some of the same characteristics. It occurs in an organism, a complex environment (analogous of the turmoil at the ocean vents), when an unfortunate combination of genetic mutations (analogous to the chance chemical precursors to life) co-opt an existing unit, a healthy cell (similar to the iron-sulfur crevaces); it's accidental, but appears to be for its own purpose (just as does life itself). It affects the DNA replicator (similar to the probable RNA replication of early life). Because it duplicates itself, like the first life that "stuck", it only has to happen once. It's not that mysterious really; cancer is simply a DNA-jack of several normal functons. It causes the cell to duplicate furiously (like young cells do naturally), it stimulates local blood supply (a normal response after injury), it resists expulsion (like any real body part), it never dies (just as stem cells don't), and it travels throughout the body (like antibodies do). And, like first life, it just takes one such freak convergence of mutations to get going. That is, to exploit its environment, and flourish.Whether first Earth life suffered the horrors of interstellar travel, or if it rose from the tortured ocean depths, it eventually escaped those nasty environments to become the first invasive species. The atmosphere was not yet oxygenated, but who cares? Life doesn't need oxygen; in fact it's a waste product, a toxin, introducted much later, by plants. Some of our bacterial ancestors moved toward complexity, toward nucleated cellular structure, intercellular cooperation, complex organisms capable of sexual reproduction, then coalitions of organisms, and when one of them developed language it burst into cultures and societies. It's speculative, but other bits may have moved the opposite direction, stripping down to survive in new niche environments -- the intestine of a particular species of insect, perhaps, in magma, or, or very near the core of a nuclear plant. Short, lean, and mean.
From this view it's easy to see humans as reckless, wasteful, ignorant, lumbering idiots, but we're also the pinnacle of complexity. We are a virulent invasive species, which has put its stamp on the planet so thoroughly that many geologists say we're in a new epoch -- the anthropocine. And we're soiling our nest, it's quite clear. We may actually manage to lumber into extinction and we wouldn't be the first. And even if we take all complex organisms with us in in a nuclear firestorm or an environmental catastrophe it gives me some comfort to think that some desiccated, dormant, space dust, or some small bacterium whose ancestors now preen near the warm core of a nuclear reactor, or some wiggly bit in magma -- will yawn, stretch, and get down to business.
And the next interesting era will skip the boring part altogether.
Now comes the disclaimer. I'm not a molecular biologist, please refer to a real molecular biologist to correct any errors herein. My purpose with this post, if any, was to give my best perspective to the most fascinating question on Earth, or anywhere, ever.