An article this week in Smithsonian got me to thinking about the scale of history and prehistory.
The topic of the article is fascinating enough on its own. Archaeologists working in the Nefed Desert of northern Saudi Arabia have discovered tracks of what was pretty close to an anatomically-modern human, fossilized in a dried-up lake bed. What's remarkable about these tracks is that the best estimate the researchers have for their age is 120,000 years.
This is a surprise for a couple of reasons. The conventional wisdom is that humans didn't leave Africa until 50,000 years ago, so this would mean our cross-continental walkabout started over twice as long ago as we thought it did. Also, it points to the Arabian Peninsula as having had a dramatically different climate back then -- along with the human footprints were the prints of elephants, camels, buffalo, and horses, suggesting something more similar to the central African savanna than the current barren desert.
But what this brought to my mind is the vastness of time. When we think of "old stuff" we tend to lump it all together. If asked to name something old that humans did, a lot of people would come up with the Egyptian Pyramids -- but these footprints are 24 times older than the Great Pyramid.
So when the person who created these prints was walking across this mudflat, it would be another 115,000 years before the builders of the Great Pyramid were born.
Our minds boggle at big numbers. The 120,000 year old footprints are still, geologically speaking, recent, still in the middle of the Pleistocene Ice Ages. Ten times further back -- 1.2 million years ago -- you're still in the Pleistocene. To reach the next age back -- the Pliocene -- you have to go over twenty times deeper into the past, on the order of 2.6 million years ago.
And still, things would be more or less like they are now. Sure, there were some odd animals lurching about -- the enormous short-faced bear and tank-like armadillo relatives called glyptodonts come to mind -- but a map of the continents wouldn't be too very different from today's.
Ten times further back than that, 26 million years ago (and 25.88 million years prior to the "extremely old" Saudi Arabian footprints), and you're in the Oligocene Epoch, the time of some of the largest land mammals ever, and finally things are looking pretty different. The aptly-named titanotheres hit their peak size with the Baluchatherium, which was five meters tall at the shoulder. This is also when the weird little multituberculates bit the dust for reasons unknown, after being one of the dominant mammal groups since the Jurassic Period.
To get back to the last of the non-avian dinosaurs, we have to go a bit over twice as far back as that -- 66 million years, or 550 times older than the Arabian footprints we started with. T. rex bought the farm during the Cretaceous Extinction, but what's kind of mindblowing is that another of the popular dinosaurs, Stegosaurus, went extinct over twice as far back as that, toward the end of the Jurassic, around 150 million years ago.
Put a different way, in terms of time, you're fifteen million years closer to the Tyrannosaurus rex than he is to the Stegosaurus.
It's why I always get a bit of a laugh when I hear people say the dinosaurs were a colossal evolutionary failure. The earliest true dinosaurs appeared in the early Triassic Period, something like 240 million years ago, and the last of them (again, other than birds) died at the K-T Boundary, 66 million years ago. So they were the dominant life forms for 174 million years, roughly seven hundred times longer than humans have been around.
Back another twelve million years before the first dinosaurs was the horrific Permian-Triassic Extinction, caused by a serious Series of Unfortunate Events -- the lockup of Pangaea changing the climate, sea level, and ocean current flow, along with a volcanic event for which superlatives fail me. It covered virtually all of what is now Siberia, burning through live vegetation and Carboniferous-era coal deposits, spiking the carbon dioxide content of the air, simultaneously boosting the temperature by fifteen or more degrees and turning the oceans into an acidic, anoxic sewer. By some estimates, 96% of life on Earth died, pretty much because a natural event did accidentally to the world's sequestered carbon reserves what humans are now doing deliberately.
Cautionary tale, that should be, but for some reason it isn't.
Over twice as far back as that -- something like 541 million years ago, or 4,500 times older than the Arabian footprints -- we reach the Cambrian Explosion, the rapid diversification that produced just about every basic animal body plan that exists today.
And that's where we'll stop, although be aware that in a trip back to the formation of the Earth, you would still only be one-twelfth of the way there.
I don't know how anyone can not be impressed by the vast depths of time, and how honestly insignificant and ephemeral we are. You are the end product of a lineage that stretches back all the way to the beginning, each generation of which lived long enough to reproduce. As my evolutionary biology professor put it, "Your ancestors all the way back had to be good at two things: surviving and fucking." (Accurate if a bit crass.)
What it all makes me think of is where it's all going. What, if we could look forward, would we see? 120,000 years, 5 million, 50 million, 500 million years from now? Highly unlikely that humans (or their descendants) will last so long; extinction and replacement are the rule, not the exception. I expect that whatever we'd see would be as weird to our eyes as the glyptodonts and pterodactyls and stegosaurs are.
But considering what the Earth's ecosystems have gone through in the past, I'm pretty sure there'll still be life of some kind, even in those far reaches of the future. And I find that a comforting, if humbling, thought.