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Frozen in time: Museum of Natural History

Imagine "Ediacara," an alien undersea world where no predators ever prowled. In this shallow ocean a common species is an animal that looks something like an elongated leaf on a stem. But the leaf is a thick structure, quilted and puffed up like an air mattress.

The leaf animals live in colonies, filtering nutrients from the water. They space themselves evenly across the seascape, far enough apart that they don't block each other's sunlight or use the next animal's food.They remain in one place, fixed to the ocean bed. Since there are no rocks they can attach themselves to, each grows a disk-like "holdfast" on the bottom of the stem.

Even the seabed is peculiar. It is a strong mat of microorganisms that stick together to form a leathery living membrane. The holdfasts of the leaf animals are beneath this mat, keeping them in place, and their bodies extend above.

Usually, nothing much happens here. It is a peaceful Garden of Ediacara.

But sometimes disaster strikes. A volcano erupts, spewing a deep layer of fine ash that flows over some of the animals and kills them.

The Garden of Ediacara is not an imaginary world, and it's not life on a moon of Jupiter or some distant planet. It was here, more than half a billion years ago, throughout the Earth.

That was a time before the Cambrian era began with a sudden explosion of life of all varieties, the violent development of active animals that hunted and were hunted. It was strange almost beyond belief.

A section of the Garden of Ediacara is displayed in a stunning new exhibit at the Utah Museum of Natural History. The very direction of the ancient ocean current is preserved in the way the animals fell under the smothering ash.

"They were buried like Pompeii, exactly where they were sitting that Thursday afternoon 570 million years ago," said professor Adolf Seilacher.

"Fossil Art," a traveling display that includes leaf animals, will be on display through Dec. 7 at the museum, located on the Presidents Circle on the University of Utah, about 200 South and 1340 East. The display is the work of Seilacher, professor emeritus of paleontology at Tubingen University, Germany, and an adjunct professor at Yale.

In 1992, the Swedish Royal Academy awarded him the Crafoord Prize - the geological sciences equivalent to the Nobel Prize. Seilacher decided to use the award money to have casts made of amazing fossils scattered throughout the world. He had excavated some of the originals himself.

He hired Hans Luginsland, a skilled fossil preparator also from Germany, to make casts of epoxy resin. Many of them are 6 feet tall. Displayed next to the museum's walls, they are like beautiful stony tapestries.

They show a remarkable variety of life signs from a billion years of Earth's history. The most ancient specimen is the only one that is the actual rock, not a cast: apparent worm tracks that Seilacher discovered.

"You see (the tracks better) in tangent light," he said last Friday, handling the rock as university technicians and Luginsland were setting up the exhibit. He tilted the brownish slab so that window light cast strong shadows, throwing the ancient curving trails into bas-relief.

"I found them in India . . . in rocks 1.1 billion years old." They are about twice as old as Ediacara fossils, previously thought to be the oldest multicelled organisms.

Seilacher said he wants Utahns to be able to touch his India specimen, so they can get a feel for that great antiquity. But he warned that they must be extremely careful with the priceless fossil.

Except for the Ediacara animals and beds of hundreds of clams, the exhibit is entirely of trace fossils - the imprints left by geology or life - not representations of the fossilized creatures themselves. There is the trial of a pre-dinosaur reptile walking across mud that cracked when it dried, deforming the tracks. If you look closely you can see spiral patterns of insects' egg cases, made when they burrowed into the mud.

"Sand volcanoes" made when differences in temperature forced sand to form little domes are among the casts. The way the domes fractured is evidence for the leathery mat of microbes that covered the sea floor in those most ancient times.

The burrows of something like a big shrimp are there, dating to 220 million years ago. They were filled with sediment that hardened, and it is this that remains, a maze of tubes that bulge into bigger elbows when the animals needed to make a turnaround spot.

Even ancient cracked mud and wavelet ripples are there, along with casts of raindrops imprints that happened to be preserved for millions of years.

"Now, our next target is raindrop impressions 3.4 billion years old," Seilacher said. He and Luginsland will head to southern Africa to search for drop imprints in rock of that age, in hopes that they will tell something about the size, and thus makeup, of raindrops back then.

Trilobites, small arthropods with light armor, scraped their many legs through the mud trying to stir up bits of food. Different species searched in different ways: small ones circled, legs going out and then pulled inward, while a larger type slid along to the side.

These trilobite tracks were frozen in time by sediments. Their forms were preserved once again, 530 million years later, when Luginsland made his casts. They are so exquisitely textured and colored that they seem to be the actual stony material.

The plowing of the sea-bottom by active animals like trilobites probably is what destroyed the strange leathery mat of microorganisms.

Seeing these odd and lovely casts is a moving experience. Making them must have been even more awe-inspiring.

"It is a deep feeling to stay by this thing that's so very old," said Luginsland, speaking of the time they went to Mistaken Point, Newfoundland, to cast the victims of the Ediacaran volcano. The Mistaken Point Ecological Reserve has huge, tilted bedding surfaces that are exposed in cliffs beside the Atlantic Ocean, according to the exhibition catalog.

The fossils are faint, with little relief. During overcast weather, which Newfoundland frequently has, or when the sun is high above, they are hard to see. But Seilacher exclaimed that about 5 p.m., when the sun is low enough to shine a raking light on the surface and the shadows bring out the forms, the view is astonishing.

"It look to you like it's living," Luginsland said. "It's a very deep feeling in Newfoundland."