Along the Way

long the Way Searching for Clues to Petrified Forest's Ancient Past

Arizona was a little different 225 million years ago. For one thing, it was full of primordial slime. The Petrified Forest, in fact most of northeastern Arizona, was a gigantic swamp laced by an intricate network of rivers, feeder streams, and lakes. Lungfish and freshwater sharks chased shrimp and minnows through the tepid water. Twentyfoot-long phytosaurs, cousins of modern crocodiles, lurked on the banks among horsetails, ferns, and ancient relatives of pine and tropical trees that looked like palms. Half-ton metoposauruses, resembling salamanders, cruised the shallow waters. Small primitive dinosaurs roamed the nearby hillsides searching for food. In slack waters of the marsh, amber quietly collected at the bottoms of stream meanders and small ponds, but no one knew that until 1990. You remember amber, although chances are you've forgotten exactly what it is. Most of us think it's a rock, sort of like quartz or agate, but amber actually is the fossilized resin of vanished trees. The ancients dug it out of pits on the south coast of the Baltic Sea, and craftsmen still turn the lustrous yellow-brown resin into trinkets and pipestems. By 1960 geologists had discovered it pretty much all over the world, except in the Petrified Forest, the one place you might have figured was a sure bet. Fact is no one had ever looked very hard for amber in the Petrified Forest, mostly because it's pretty well hidden. It's small and encased in thick mudstone. To find it, you have to start byguessing it's there. And you'd better have a pretty clear idea which rocks contain it because if you're serious about finding amber, you're going to spend several years hauling a lot of heavy mudstones to a lab, cracking them open, and inspecting the debris through a microscope. Even a geologist needs a good reason to look for amber that tiny and hidden so well. Ronald J. Litwin and Sidney R. Ash are geologists, and they've got a good reason (and a permit from the National Park Service): they want to understand the ancient environment of the Petrified Forest. They hope to put the past back together piece by piece. After years of painstaking analsysis, they recently found bits of amber at two sites in the Petrified Forest. A big piece is about the size of a pea, but small as they are, those granules may be the missing pieces to the puzzle Litwin and Ash want to solve. Litwin is with the United States Geological Survey; Ash is a professor of geology at Weber State University in Utah. Between them they've studied the Petrified Forest for 35 years. That may seem long, but to amber it's just a notch on time's arrow. Baltic amber is 25 to 50 million years old, and it's practically juvenile compared to the amber in the Petrified Forest. The trees it oozed out of died around 225 million years ago, about the same time the earliest dinosaurs started eating their way up the food chain. Most trees of the Petrified Forest didn't actually grow there. They washed down from highlands farther south, probably victims of volcanic eruptions that would have made Mount Saint Helens seem like a hiccup. The trees were araucaria, big evergreens that disappeared from our hemisphere a few eons ago, but which are still found in the Southern Hemisphere, especially Australia, that warehouse of relict species. For Litwin and Ash the question of the moment is, where did the amber come from? On one hand, araucaria are known to have produced amber throughout the world. Furthermore, chemical analyses indicate the mudstone amber is closely related to the sap of existing araucaria. Still Litwin and Ash can't quite bring themselves to claim their amber came from the petrified araucaria because, frankly, the picture is confused. The two didn't find their amber in any of the main forests of petrified wood, something they might expect if the stuff came from araucaria. Another puzzle: they have also found amber in a fossilized cycad leaf, a completely different kind of plant from araucaria. Maybe cycads produced the amber locked in the mudstone. A fine point of science is at work here. Unless Litwin and Ash actually find amber in a tree or get indisputable chemical evidence for its origin, they just can't be sure where it came from, and science is all about being sure. Litwin and Ash really hope to find parts of lizards, spiders, or insects in their amber someday. Then they might learn something really new about the environment of Arizona all those eons ago. Plant leaves, pollen, and flowers also get stuck in amber and emerge later to delight geologists. In the Dominican Republic, investigators once found a 10-million-year-old frog encased in amber. What are riches compared to that? Litwin and Ash think of themselves as detectives. Amber, pollen, fossil critters, fossil plants, all are clues. The mystery is the past. The key is the present. Litwin says that when he walks the arid lands of our modern Petrified Forest National Park, his mind swims through an ancient marsh whose details he will never quite see. Picture him on an island in time. Stone trees, amber, and dinosaur bones share space with tourists crossing a desert park. The geologist sorts them out. He just wants the facts.