Geology And Geophysics

A Guide to Backyard Geology



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Poured onto the glass slide of a microscope, a thimbleful of sand becomes a cornucopia of remarkable tiny objects. Pierced cartwheels, clams and thin shelly tubes. Fractured clumps that resemble miniature bunches of bananas. You can find snails in a bewildering variety of colors and sizes, rolling around like marbles with the nudge of a pin amid the scattered calcite rhomboids. There is the occasional windblown quartz sphere, as beautiful as a tiny crystal ball. This is a teeming zoo of insignificant life forms, frozen in time, like characters in a cryptic message from a half a billion years in the past.

Then, amid the scatter of debris, you spot something. Impossibly sharp, polished like a piece of translucent bone, fishhook-curved and buttressed with delicately engineered grooves and projections, it is a jewel-like object of incredible beauty - a tiny fang from a fossil ocean. You have found the tooth of a conodont.

You are not be first to discover one. That pleasure went to the Russian scientist, Dr. Christian Pander in the year 1856.

Nevertheless, to spy a conodont is to experience a sudden, illuminating vision into one of the strangest eras of life's past, when the land was barren desert and the first animals were stirring within the brackish seas. Delicately layered lines visible through the glossy surface, cracks and pits in the whitened tooth enamel - these are the physical evidence of a roving predator's hunger, its travels and destiny.

Does discovering the toothy fossil of an ancient hunter seem like an impossible dream? Guess again. You might be surprised to find that rocks in your own backyard might contain tiny, ancient objects that are as vicious-looking as any Tyrannosaur jawbone - and are ten times older.

These remarkable teeth belong to extinct marine creatures called conodonts. Tiny, jaw-like structures the size of a grain of sand, these "cone-teeth" were the first cellular bone ever to be deposited in ocean sediments during the Paleozoic era about 250 to 500 million years ago, first appearing long before land animals, fish or other creatures with backbones. (Dinosaurs became extinct about 65 million years ago.) Conodonts may have been ancestral to modern vertebrates, and their teeth were complex structures that were clearly specialized for many different lifestyles, with durable chemical composition that allowed them to pass this tremendous span of time almost unchanged. Although complete fossils of the complete animal are quite rare, poorly preserved imprints suggest an eel-like creature with up to 7 different kinds of tooth element clustered together in the head to form a bizarre feeding apparatus unrelated to modern jaws. Conodonts may have been minnow-sized, with two large eyes, with chevron-shaped markings along the body suggesting muscle blocks found only in chordates. Although some researchers think conodonts may have been related to the hagfish or "slime eel," these creatures were quite different from anything alive today, and conodonts are still a major mystery to paleontologists.

One thing is certain - conodonts lived on a very different kind of world. During the Ordovician era 450 million years ago, the Earth's rotation was slightly faster. The air had a different pressure and composition. The continents were arranged differently, with vast shallow oceans filled with a bewildering variety of strange organisms - thousands of species of filter-feeding, clam-like brachiopods amid crumbling islands of sponges and coral-like bryzoans. In other areas dense "flower gardens" of armored crinoids swayed gracefully in the currents. Bottom sediment was inhabited by burrowing worms, snail-like cephalopods and early segmented animals such as the extinct trilobites. The land would have been a barren, almost lifeless environment with very primitive mosses inhabiting low swampy regions. The wide variety in conodont teeth suggest that even at this early stage in the evolution of life, they were part of a complex ecosystem of predator and prey, although most of the creatures that made up their diet probably had soft bodies that left no fossils. Whatever their origins, these small, beautiful objects offer tantalizing clues about a world that seems as remote as an alien planet, yet is as close to us as the sand below our feet.

If you want to find you own conodonts, you must first locate an outcropping of well-weathered rock that contains paleozoic fossils. Such rocks are abundant in many areas of the central United States. Many professionals use acetic acid to dissolve conodonts out of limestone. (Don't use hydrochloric acid - it will etch and destroy the conodonts). You can use household vinegar, or buy inexpensive industrial grade glacial acetic acid and cut it to 10% strength. (Use an area with good ventilation, and always use gloves and eye protection!) Break the rock into centimeter-sized chunks, and put the fragments into a small bucket with holes in the bottom and soak it in a larger bucket of acid for a few days. Then lift the bucket out to drain, pour off the liquid, and repeat the process. After a few weeks, you should find enough sandy residue to sieve, clean and inspect.

Rock that has large fossils will probably contain microfossils too. Productive residue should also contain tiny gastropods or shell fragments. Several small samples are best - if you find just barren rock, go on to another sample. Locate productive areas and then return for larger samples later.
I have had success simply scooping up samples of crumbling soil and limestone from old road cuts - materials that are often rich in heavy conodonts that remain when lightweight clays have been washed away. Once you have obtained enough residue or sediment, it is time to pan for conodonts. You will need two screens - a wide 20 mesh and fine 80 mesh filters to sieve out the conodonts. You can buy suitable sieves from the Carolina Biological Supply Company, but true-blue do-it-yourselfers can try using a fine mosquito screen as your coarse screen, and fabric from an old pair of women's nylon stockings as your fine screen. Stretch the fabrics over a couple of crochet loops, stack them together with the fine filter underneath and wash the sediment through the two filters using a gentle stream of water. (Be sure to do this outside so that you won't destroy your plumbing.) The evenly graded sandy material trapped between the two filters may contain conodonts. Collect about 50 grams of this material, dump it into a flask and and carefully flush off any organic material by repeatedly swirling and pouring. Clean and sterilize your sediment by boiling the residue for a few minutes in a flask with a few grams of dishwashing soap. Wash the material again by pouring the sediment over your fine filter and rinsing off the soap and clay. Then allow the remaining sandy material to dry. Professionals further concentrate their conodonts several fold by using heavy non-toxic liquids such as Sodium Metatungstate to float off the lighter parts of the sediment inside a separation funnel.

When you are ready to look for conodonts, sprinkle the dried material into a thin layer on a card, and scan it under the microscope. You will get best results with a binocular dissecting microscope that allows you to inspect large areas of sediment, brightly lit from above. Improve your efficiency by sticking a piece of graph paper to the card so you can scan systematically. If you have picked productive rock, you should find an interesting assortment of tiny snails, bits of bryzoan, and silica fragments. If conodonts are present, you should begin finding them within 15 to 20 minutes. A spoonful of material can contain hundreds of conodont elements - but similar looking rock only inches away can be barren of specimens. A good way to file your collection is by using paleontological micro-slides small cardboard slides with an aluminum clip to hold a glass slide in place to protect your specimens.

Use a fine, slightly moistened paintbrush to pick up the conodonts, and touch the brush to small cardboard slides lightly coated with diluted white glue. Like snowflakes, each conodont is a unique and fascinating sight. You are looking at the teeth of an animal that roamed the warm seas a half billion years ago!

Although museum-quality fossils are out of reach of most of us, conodonts are often easy to find and fascinating to study. After discovering them in the soil of my own yard here in Nashville, Tennessee, I decided to make their study a hobby, and ten years ago I created a website to organize and display my collection. Over the decade, I have gotten many visitors who have looked for conodonts. Some are from scientists or teachers who have borrowed pictures for their publications. I have heard from researchers in Antartica, and backyard geologists. I have gotten a chance to meet some of the handful of serious researchers that publish today on this most arcane of topics.

Sadly, I never published any original discoveries, and my interests over the years have wandered to other topics. Nevertheless, my efforts left an unexpected legacy. My website still appears at the top of the list if you "google" the word "conodont, offering information to students and enthusiasts - more than 50,000 of them.

And of course there is the small box in my basement. It contains treasure - hundreds of slides covered with tiny, magnificent relics of the Paleozoic.

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