Welcome to Jurassic High: how do teen fossil hunters know where to dig for bones?

How do teen fossil hunters know where to dig for bones? "Sedimentary, my dear!"

Last summer, a group of fossil hunters scoured the "badlands" of eastern Montana in search of dinosaur bones. On the high-and-dry prairies, one geologist stumbled upon a bone embedded in rock. From the bone's weathered look, the geologist decided it was useless--and took a pass.

But a gut feeling made his partners Simon and Sarah White, a brother-and-sister duo, curious about the bone. They started to chisel and hammer away. Before long, they unearthed the bones of a hadrosaur--a duck-billed dinosaur!

Sarah and Simon White aren't paleontologists--scientists who study fossils of prehistoric plants and animals. Simon, 17, is a senior at the Webb Schools in Claremont, California. Sarah, 19, graduated from Webb in 1996. That's where they learned the ropes of fossil hunting.

Simon and Sarah excavated for seven days straight. Their hadrosaur treasure trove included three complete leg bones, many fist-sized toe bones, a pelvis, and several vertebrae (back bones)--including a tail stretching more than two meters (7 feet)!

"You uncover a little bit and you just want to keep going," Simon says. The biggest surprise: On the dinosaur's heel the teen diggers found an imprint of the animal's skin--a very rare discovery. Only 11 or so dinosaur skin imprints have been discovered since the early 1900s. "It looks kind of scaly, almost reptilian," says Sarah. From maps, the teens knew the rock's age to be 66 million to 67 million years old. So they were able to guess that the hadrosaur fossil formed around that time, too.

Fossils are the remains of plants and animals usually preserved in rock. Paleontologists study fossils to uncover mysteries about life on Earth: When did life begin? How has life changed over billions of years? What did prehistoric creatures look like? Where and how did they live? Why did they disappear?

Even though fossils can be found in every state of the U.S., experts believe only a small percentage of prehistoric plant and animal species have been preserved as fossils. Many species died out without leaving fossil traces at all. That makes Simon and Sarah's skin-imprint find even more spectacular. "Skin impressions are rare enough, and this one is on the skeleton, so we can tell what species the skin is from," says Donald Lofgren, a paleontologist at the Webb Schools.

JURASSIC STUDY HALL

How did these two teens become expert fossil hunters? Webb is a private boarding school of 325 students--and the only high school in the world with a paleontology museum right on campus! Students not only can take paleontology classes, but dig in to their fossil finds after school in the museum. In the "prep" lab they learn how to clean, preserve, and display fossils.

During the school year, students and teachers may spend long weekends on fossil digs in California deserts. But in summer their fossil trips last 20 to 30 days, and stretch from Arizona to Montana. And their finds are ding-mite! Each year they haul back 200 to 300 fossils--which account for 95 percent of the museum's 100,000 specimens.

Part of the students' success is learning the best--and worst--places to sleuth. For instance, it would be almost impossible to discover fossils in igneous or metamorphic rock, says Scott Kirby, 16, a junior at Webb. Igneous rock (such as granite) is formed by the cooling of molten magma--semi-liquid rock deep within the Earth. As magma rises through the Earth's crust, through cracks or volcanoes, it melts and destroys any remains of organisms before they can fossilize. When metamorphic rock (such as marble) forms, intense heat and pressure in Earth's crust alter or "morph" the composition of other rock minerals--and so long, fossils!

SO WHERE DOES ONE LOOK:

"Limestone, sandstone, and mudstone are the best places," Scott says. All three are examples of sedimentary rock, rock made from layers of compacted sediments. Carried by rivers, oceans, and wind, these minute eroded morsels of rock are deposited with sand and mud--and the remains of plants and animals. More layers of sediment pile up and compact (press down) the lower layers. Meanwhile, minerals cement the sediments to form sedimentary rock.

FROM DINO TO FOSSIL

Sarah and Simon discovered their hadrosaur fossil in a bed of sandstone--sedimentary rock with the consistency of cemented beach sand. The story of how their dinosaur became fossilized might go something like this:

After a final snack on some giant ferns, the hadrosaur collapsed on a riverbank. Sediments quickly covered the dinosaur and protected it from scavengers and bacteria. The animal's flesh decayed except for the one patch of skin by the heel.

Before the skin rotted away, it left a scaly imprint (like a handprint) in the sand. Normally, the bones would decompose too. But more sediments carried by the stream preserved and protected them. Meanwhile river water flowed through the bones, dissolved their calcium, and deposited rock-hard minerals in its place. The bones became petrified remains--hard, rock-like fossils.

Over millions of years, layer upon layer of sediments piled up, forming a sandstone "tomb" around the dinosaur. Eventually, forces within the Earth pushed the sandstone above the water level. Wind and rain eroded (wore down) the sandstone, until a piece of hadrosaur bone poked through the surface. Then, millions of years later, a team of fossil hunters from the Webb School just happened to wander by . . . and the rest is history!

For a virtual tour of the Webb Museum, check out this Web site: http://www.webb.org/webb/

RELATED ARTICLE: Bone Dry

How does this fake fossil compare with a real one?

WHAT YOU NEED

water, sand, sponge, scissors, aluminum pan, Epsom salts 

WHAT TO DO

1. Cut sponge into shape of a bone.

2. Place the "bone" in the pan and cover it with sand.

3. Mix 1/2 cup Epsom salts with 1 cup warm water.

4. Pour the salt water over the sand and let dry a few days.

5. Dig out the bone and dust it off.

6. Make a chart to compare the similarities and differences between your "fossil" and a real one. Some variables to consider: age of fossils, process of fossilization. What else?

RELATED ARTICLE: Find That Fossil

Fossils, the imprints or remains of plants and animals usually preserved in rock, form in a variety of ways:

Petrified remains

Example: Dinosaur bones

How they form: Water and dissolved minerals flow through bones--a process called petrifaction. The water dissolves the bones' calcium and deposits other hard minerals like quartz in its place. Result: rock-hard bones.

Molds and casts

Example: Cast of a seashell 

How they form: Seashells sink into sediments, a mix of eroded pieces of rock, sand, and mud. The shells are buried by layer after layer of sediments. Over time, the sediments compact and turn to rock. Cracks in the rock allow water to reach the shell and dissolve it.

That leaves a hollow cavity--or mold--in the rock. More sediments fill the mold, harden into rock, and produce a cast--a copy of the original shell.

Carbonaceous films

Example: Carbon outlines of fish, plants, soft-bodied creatures

How they form: When sedimentary rocks form, heat and pressure force gases and liquids out of a decaying organism. All that remains on the rock is black carbon residue in an outline of the original organism's body.

Trace fossil

Example: Insect trapped in amber

How they form: Trace fossils are imprints rather than actual remains of living things. For example, dinosaurs have left tracks in soft mud that hardened into rock. These fossils tell us how animals lived, rather than what they looked like. For instance, did they run or walk? Did they travel in herds or alone?

Original remains

Example: Insect trapped in amber

How they form: In rare cases, actual organisms, or parts of them, are preserved. One way is mummification, when dry sand or chemicals preserve an animal's skin and other tissues. Sometimes insects are trapped in amber, the hardened resin of ancient trees. Fossil experts have also discovered remains of woolly mammoths frozen in ice for thousands of years.

RELATED ARTICLE: Mystery Fossils

Play a fossil guessing game.

WHAT YOU NEED

modeling clay * "Mystery" Objects (like clothes pins, buttons, paper clips) * paper and pencil

WHAT TO DO

1. Get into groups of three. Your teacher will hand each group a paper bag with an object inside.

2. Each member of the group should flatten one lump of modeling clay.

3. Take the "mystery" object from the paper bag.

4. Each member of the group should press the object into his or her slab of clay, making an imprint. Make imprints from different angles (like those of the clothespin, above.)

5. Your teacher will place the slabs on numbered scraps of paper and display each of the objects on a table.

6. Silently match the imprints with the objects, recording your choices on paper.

CONCLUSION

What makes some imprints easy to identify, others hard!

DON'T STOP NOW!

Paleontologists are fossil detectives. How do you think they examine fossils for clues?