We shouldn’t exist. We really shouldn’t. But through the stroke of evolution, combined with the right place at the right time, with the right temperature and the right elements, we’ve come to fruition. The process hasn’t been too quick, in fact, taking millions upon millions of years. Nearly every science program you watch mentions how human life occupies such a small strand of history, compared to everything else. We weren’t here when the first life forms were, nor was the earth sustainable in any way for us. If you were to take a time machine back to a Pre-Cambrian wasteland the atmosphere would be so full of hostile elements and toxic vapors that you wouldn’t be able to survive. So much for all those time travel films.
It took the proliferation of oxygen, released from small bacteria, to establish a new form of organism that relied on it, also mixing with another vital element: hydrogen. But oxygen can actually kill certain organisms that don’t rely on it. These, so to speak, went the way of the dinosaurs. Prokaryotes (non nucleic cells) gave way to eukaryotes (nucleic) with mitochondrion soaking up the oxygen and using it for energy. Think about how crazy it is that something we’re dependent on now was once toxic. Also think about how crazy it is that the dying out, or extinction, of certain organisms was necessary for the advancement of new ones, leading to us.
In addition there was the fact of the earth’s surface constantly shifting and being battered by meteorites and chunks of debris. If at any point we were at a different position in space, one just big enough (and we’ve big hit by plenty) might have struck us with a factor of “times Hiroshima.” There, have in fact, been extinctions throughout Earth’s history. The largest one was the Permian extinction, wiping out most animal life forms. It is estimated that, even with our extensive study of fossil record, there are still thousands of prehistoric life forms that were taken off the map, not just because fossils are so rare to form, but as a result of these cataclysmic events. One of the best-known results of prehistoric extinctions is that the dinosaurs went out the window. But they were actually survived by turtles, you’ll be interested to know. They were among one of the few land species to survive (including crocodiles), but many water species thrived afterwards. Something just as simple as water (but not so simple when you really think about it) was responsible for the protection of certain organisms after the dinosaur extinction. And the extinction basically allowed for other organisms to step in and take the place of their predecessors. It’s pretty crazy to expect an influx of new life forms on a planet that nearly just got purged of them. It’s almost like wiping a slate clean and seeing new words form in their absence. In Earth’s case, the slate was never completely clean. But it nearly was.
Another truly mesmerizing thing about life on Earth is its variety. So much of it is utterly microscopic that we’ll probably never discover it for the rest of human existence. In fact, most life is still waiting to be scrutinized somewhere, perhaps someday with the proper technology.
The separation between Cambrian and Pre-Cambrian revolves around an explosion of complex organisms that occurred about 540 million years ago and supposedly (depending on the theory) has every implication for life as we know it today. This theory was also assisted by the discovery of the Burgess Shale, made in 1909, by scientist Charles Doolittle Walcott. The Burgess Shale showed the widest array of fossils ever uncovered and, to add insight, a large variety of different forms. However, many of the forms were unrecognized and had failed to pass the evolution test for survival. Yet they were all here, gathered together in one place, and it was proposed that all permanent life forms that we see today are the result of a sporadic burst that had seemingly occurred here. It was later found that the life forms were, in fact, not completely new life forms, but more than likely larger and luckier versions of their predecessors, debunking the “Cambrian explosion.”
When you think about all of these factors it really is insane that we’re all here, alive and well. Well, at least some of us, biologically speaking. Very few. In a number with millions and millions of digits (and I’m likely off here), any slight adjustment would turn the lights out and wipe out the entire arrangement. If the earth were, say, five percent closer or farther from the sun, that could be the difference between scorching alive (or dead, as it would be) or living in an eternal ice age much harsher than any ice age we’ve ever had. The right elements have to be in the atmosphere at just the right concentration. The right organisms have to die at just the right time. And the calculation is always increasing as time goes on and more factors are added to the puzzle. But the puzzle always manages to keep us intact. Well, at least for now. We can only hope, for a long damn time.