Look at the picture above. What do you see? Tire tracks? Snakeskin? Something else?
The image above is a fossil. But it’s not the kind of fossil you can pluck out of a rock, like a bone. It’s the fossilized cast of an organism, created after an imprint of the creature later filled up with sediment. And it’s among the rarest of the rare: The organism that made this infilled imprint lived around 550 million years ago.
This fossil is of Gaojiashania cyclus, a wormlike creature that crept over ocean sediments long before living things evolved the ability to build hard shells. Its squishy body had nothing that could turn to stone; the only way we know these organisms existed is because scientists have found impressions of them—some that filled to make casts and others that remained hollow—in sediments.
These fossils are tiny, so how exactly do scientists find them? One tip: Be patient and search in low-angle sunlight, said Emmy Smith, a paleontologist at Johns Hopkins University in Baltimore, Md.
Smith has spent the past 3 years searching for evidence of these creatures. The hunt “is a little bit of a wild goose chase,” she said. The trick to finding the tiny fossils? Nothing, Smith explained, beats a healthy dose of serendipity.
Fossil Hunting Tips
Tiny fossils of these ancient worms have ridges that cast shadows in low-angle light, so prepare to stand outside for hours, picking up rocks and turning them every which way, Smith said. “If the Sun is directly overhead, it’s very difficult to see these fossils.” Some of the fossils are the size of fingernails but are recognizable to Smith’s trained eye.
The most important tip of all? Don’t go out specifically searching for these rare fossils. Start your field adventure with a different question in mind. For example, what kinds of environmental changes signaled the end of the Ediacaran and the start of the Cambrian period about 542 million years ago?
Then, just hope for a big find, Smith said.
Smith got that big find in 2014 while on a field trip outside Gold Point, Nev. The town’s population, which reached about 14,000 at the height of the gold rush, now ranges from 4 to 8, depending on the season.
There, Smith discovered a fossil of a wormlike creature called Conotubus that lived during the last 10 million years of the Ediacaran period. Analysis of the ancient fossil also showed that it is a fossil like that of a dinosaur bone—minerals directly replaced matter within the organism. The specimen is among the first of its kind to be discovered in the United States.
“So many people have been to these sections” outside of Gold Point, Smith said. “It’s sort of surprising to be finding all of these different early forms of life” just 300 kilometers from the Las Vegas strip.
Why does Smith hunt for the tiny tubes, anyway? Smith studies the boundary between the Ediacaran period and the Cambrian period and what environmental changes might have occurred over that boundary.
Cambrian creatures were the very first to host body shapes similar to today’s arthropods: invertebrates comprising everything from centipedes to crayfish to crabs. The Ediacaran, meanwhile, hosted some forms of life completely unfamiliar to us. Scientists call them the “Ediacaran biota.”
Researchers know that these two groups of creatures overlapped. For example, soft-bodied G. cyclus has familiar forms that we associate with Cambrian creatures, although it predates the Cambrian’s onset. Although G. cyclus and other tube-shaped organisms like it lived during the Ediacaran, it is not what scientists consider Ediacaran biota. Members of the Ediacaran biota may have looked more like ridged disks—nothing like anything that exists today.
One of the biggest questions surrounding the Ediacaran biota is simple: Why did they disappear? And why did the Cambrian creatures (our ancestors) survive? Was it climate change? A huge disaster like volcanism or a meteorite?
Two leading theories attempt to explain the Ediacaran biota’s extinction, Smith said. One involves simple competition. Maybe Cambrian animals were simply better equipped to live in their ancient aquatic environment. Maybe they got all the food and stole all the resources, until the Ediacarans died out.
Another hypothesis is an environmental one, much like how large dinosaurs went extinct. Maybe an environmental change wiped out Ediacarans, and the Cambrian creatures, like the mammals that lived with the dinosaurs, blossomed to fill empty ecological niches.
To answer these questions, Smith and other scientists go fossil hunting. Their goal is to examine the chemical properties of the rocks in which the fossils reside; chemical changes within those rock layers could point to widespread environmental disasters that signaled Ediacaran doom.
Fossils of G. cyclus and other wormy creatures of the late Ediacaran are not the only fossils that Smith has found. She’s also discovered fossils of the Ediacaran biota, here in the United States. And Smith couldn’t have found these specimens without a bit of luck.
This story begins 14 years ago, with a structural geologist named Jeremiah Workman and his wife, Nichole. The pair were hiking just outside Pahrump, Nev., while Jeremiah was studying the landscape for the U.S. Geological Survey’s National Cooperative Geologic Mapping Program. On the long hike back to their car, Nichole spotted some interesting-looking fossils in a slab of rock about a meter long. The rock came from a unit that Jeremiah knew dated to the Late Cambrian.
“It was getting dark, I was tired, and not particularly interested in fossils from the Cambrian,” Jeremiah told Eos. “See what I knew?”
Jeremiah’s backpack was full, so Nichole “carried it in her arms down the steep, rocky hillslope,” Jeremiah said.
For 14 years, the slab sat in various places in the Workman household, even spending 5 of those years on their porch “exposed to harsh Colorado winter weather,” Jeremiah said. Then, in 2014, after Smith contacted Jeremiah about something completely different, he sent her a picture of the slab and asked whether it was anything interesting.
When she received the pictures, Smith did a double take. She saw what the Workmans had not: The ridges and dips scattered across the rock were extremely rare fossil casts of the Ediacaran biota. “I was like, ‘Oh my god, people have been looking for these for decades,’” Smith said.
She rushed out to Denver, Colo., where the Workmans live, and collected the slab, carting it to Washington, D. C., where she worked at the Smithsonian Institution at the time. During the next field season, in 2016, Smith and a team visited the site outside Pahrump and ended up finding many more fossils of the Ediacaran biota.
The team’s findings published this summer in Proceedings of the Royal Society B. But none of the specimens they found were so well preserved as those in the original slab, Smith said.
Watch Where You Step?
Finding Ediacaran and Cambrian fossils in Nevada opens up the southwestern United States as a new place to find these extremely rare signatures of life, Smith said. Scientists have found these fossils only in a few other remote places in the world, like the Australian Outback and the deserts of Namibia. Gold Point and Pahrump, meanwhile, are relatively easy to access. She plans to go back to both these locales to hunt for more fossils of the Ediacaran biota.
Now that people have a clear idea of where to search and what to look for, Smith expects that more fossil hunters looking for rare specimens may comb the Nevada wilderness. Here Smith gives us our final tip: Don’t worry where you step.
“Because they’re so rare and in remote places, I don’t worry that people are stepping on them,” she said.
—JoAnna Wendel (@JoAnnaScience), Staff Writer