Post by Steven K.

If you’ve been following events at Aurora Public Library this summer, you definitely know that libraries rock. Maybe you attended the classical piano concert with Ammiel Bushakevitz at Central, or the John Williams and American Film Music program at Mission Viejo, or one of the many Libraries Rock programs with Bradley Weaver. Whatever your fancy, this year’s Summer Learning Program has been a wild, musical success. (If you’ve missed all this, don’t fret! There’s still time to check out more of our musically-themed programs through the end of July. Visit our Programs and Events page for more details.)

But maybe music isn’t really your thing. (Hard for a musicophile to imagine, I know, but it’s totally a thing.) Or maybe you’re just looking for a change of pace, or a reprieve from the constant audio-bombardment from advertisers and disc jockeys and people who blast music from their smartphones sans headphones.

If so, another way to engage with our Summer Learning Program is to come to Central and check out our rocks! For while it’s true that libraries rock, rocks also rock, and our library’s rocks especially rock.

First, let me apologize for that. Second, allow me to explain.

There’s no denying that rocks have an image problem. They’re literally the most common thing on the planet. They’re used as a metaphor for stupidity. Breaking rocks was once a common form of punishment. And I mean, really, they just let people walk all over them. (Again, apologies.)

Sure, rocks might seem dull at first, but once you get to know them a little they can be positively fascinating. Layers of sandstone and limestone might not grab your interest at first, but let a river cut its way through them over several million years and you get the vast beauty of the Grand Canyon. If you haven’t been living under a rock for the past few months, you’ve probably watched the news and seen rocks being born before your very eyes on the island of Hawaii. Climbed one of Colorado’s 58 fourteeners lately? Imagine what the view would look like when the Rockies were new to the continent and twice as tall are they are today.

Canyons, volcanoes, and mountain ranges are all breathtakingly sublime. Sadly, we can’t fit these in our library—but we can fit something just as wondrous, albeit on a much smaller scale. Many somethings, actually, things that used to be very much alive but are now very much dead and have had all their living tissues completely replaced with rock. Yes, you’ve guessed it: we have fossils!

More specifically, we’ve got trilobites—and they are some of the coolest animals to have ever graced planet Earth. So what, exactly, are they? To put it plainly, they’re very ancient sea bugs. But they’re also so much more than that.

For starters, here’s what one looks like:

You might recognize them from high school earth science textbooks or from a trip to your local natural history museum. In fact, they’re one of the easiest fossils to identify, thanks largely to their anatomical namesake. The word “trilobite” is deceptively simple; it just means “three lobes” and these lobes are easy to spot on a fossil. There’s a raised lobe in the middle (the “axial” lobe) and two other lobes to the left and right (the “pleural” lobes). Coincidentally, trilobites also have three main body sections: head (“cephalon”), body (“thorax”), and tail (“pygidium,” which is just stupid fancy Latin for “rump”). Depending on the species—and also on how well- preserved the fossil is—trilobites will have various forms of eyes, legs, antennae, and spiky spines (that were probably used for defense but could have served other purposes as well).

But to me, one of the most amazing facts about trilobites is how ancient they are. The oldest specimens paleontologists have found (so far) date back to the early Cambrian period, over 540 million years ago (Fortey, 2000). That’s almost incomprehensibly old. Just stupid old. 

Imagine that you could walk back through geological time, with each step you take accounting for one year of history. To get back to the Middle Ages and chill in a castle, you’d need to walk about 3 city blocks. Watching the pyramids being built would cost you 2 miles; seeing the end of our latest ice age would be 5 miles; meeting your first fully-modern human ancestor would be a punishing 88-mile trek. But to get back to the Cambrian and swim with the trilobites, you would literally need to walk to the moon—all 240,000 miles of it. They’re that old.

Our trilobites aren’t quite that old, but they’re still ancient. Based on the identifying characteristics of the species we’ve got, they’re probably about 400 million years old—about three-quarters of the way to the moon in our thought experiment—which places them in the middle of the Devonian period (Gon III, 2009). (Take this with a grain of salt, though. I’m not a paleontologist—I’m just a nerd.) They’re also probably from Morocco, which today is a serious hub for trilobite fossil hunters. But 400 million years ago, what’s now Morocco would have been unrecognizable, because at that time it would’ve been in the Southern Hemisphere and covered by a shallow sea—which was good for our trilobites, since they were exclusively marine animals. It’s also good for us, because seafloor conditions are great for making fossils. Well, relatively speaking.

In reality, fossilization is tricky business. As Bill Bryson puts it in his delightfully accessible "A Short History of Nearly Everything"(2005): “It isn’t easy to become a fossil. The fate of nearly all living organisms—over 99.9 percent of them—is to compost down to nothingness. [...] Even if you make it into the small pool of organisms, the less than 0.1 percent, that don’t get devoured, the chances of being fossilized are very small” (p. 403). Scavengers, microbes, oxygen, and exposure are generally unforgiving to the recently deceased. The key to successful fossilization, then, is quick burial, which prevents things from nibbling away at them long enough for minerals to slowly replace all the once-living tissue. And as it turns out, quick burial is more common on the seafloor, on account of falling sediment, changing tides, churning currents, storms, mudslides, and the like. Had trilobites been land-dwelling creatures we might not have known much about them at all.

But there’s something else about trilobites that makes them the “old reliables” of the fossil record. Unlike many of their contemporaries, trilobites’ shells were infused with calcite—the same hard mineral present in clam shells and limestone. Even their eyes were made of calcite, in a crystalline form that made them some of the first animals to see complex images. In life, these rocky shields protected them from predators; in death, they staved off decomposition and, through the eons, preserved an amazingly rich fossil record for us to study.

And how very rich it is! Paleontologists have identified and cataloged about 20,000 distinct species of trilobite belonging to 10 fantastic orders. The smallest species could be as small as a millimeter long, while the biggest could grow to over 2 feet long. (Most were 1-3 inches long, though, including those we have in our small-but-charming collection.) They were also tremendously successful animals, in terms of evolutionary success and global distribution.

Collectively, they scuttled about our oceans for 300 million years—that’s twice as long as the dinosaurs ruled the earth—and their remains can be found on literally every continent on earth, even Antarctica. They were at last defeated 250 million years ago by the Permian Extinction, the so-called “Great Dying” that wiped out 95% of marine life. Since then, no trilobite has crawled along the seafloor or looked through their remarkable crystal eyes.

They may be long gone, but thanks to trilobite fanatics around the world they’re certainly not forgotten. If I’ve piqued your interest and you want to see what all the fuss is about, come visit us at APL Central in July! You’ll find our trilobites on the lower level near the 750s in the nonfiction stacks. Also, if you’d like to learn more about our ancient friends or more about prehistory in general, come visit me at the Reference Desk and I’ll be happy to indulge you.

Don’t take this opportunity for granite! (That’s the last one, I promise.)

References:

Bryson, Bill. (2005). A short history of nearly everything: Special illustrated edition. New York,
NY: Broadway. Pp. 403-417.

Fenton, Carroll Lane and Fenton, Mildred Adams. (1989). The fossil book. New York, NY:
Doubleday. Pp. 192-212.

Fortey, Richard. (2000). Trilobite! New York, NY: Knopf.
Gon III, Samuel M. (2009). “A Pictorial Guide to the Orders of Trilobites.” Retrieved from
http://www.ps-19.org/Crea11Phyla/References/TrilobitePictorialGuide2009.pdf.