PORT REPUBLIC-- --Robert Hazen searches for the origins of life on Earth - a job that takes the astrobiologist around the world, collecting the fossilized remains of long-departed creatures.
But one of his favorite discoveries turned up near the back door of his vacation home atop Calvert Cliffs: two fist-sized teeth from a great white shark that prowled the ocean that once covered Calvert County.
"That tooth was part of a living, breathing thing 20 million years ago. That tooth tasted blood. That tooth was part of a mouth that was constantly eating things," says Hazen, whose cliffside house is filled with teeth of ancient mako, great white, sand and tiger sharks.
Hazen, 58, a scientist at the Carnegie Institution in Washington and author of more than a dozen books, routinely combs the beaches where amateurs and professionals alike search for the fossilized remains of marine life buried in sediments during an era known as the Miocene.
"We think it's the best marine Miocene exposure, or collecting area, in the world," said David Bohaska, a paleontologist with the Smithsonian's Museum of Natural History.
During that period, what is now the Atlantic Ocean extended as far west as Washington, D.C.
When that tropical ocean receded millions of years ago, the sediments it covered emerged to form Calvert Cliffs, a 30-mile range that runs south along the edge of the bay, from Fairhaven in Anne Arundel County to Drum Point, Bohaska said.
The cliffs are eroding at the rate of a foot a year, and as they erode, they wash onto the beach, exposing the fossilized remains of the sharks, whales, dolphins and other marine creatures from that ancient period.
Fossils from the cliffs are displayed at the Natural History Museum's Life in the Ancient Seas exhibit in Washington, as well as at the Calvert Marine Museum in nearby Solomons.
"We have scientists from all over the world come to look at specimens from that area," Bohaska said. "And scientifically significant fossils are still being found there."
But as serious as they may be, scientists share the cliffside beaches with school groups and other amateurs who know a great outing when they experience one.
"It's all pretty cool," said 12-year-old Michael Lamond, one of two dozen students at Bayfront Park in Chesapeake Beach recently as part of a school group hunting for fossils.
Like other fossil hunters, Michael and friends in the Calvert County summer school program were after sharks' teeth and the lessons they offer. "We're focusing on what sharks' teeth can tell us about the past," said Tom Harten, an environmental education teacher.
Sharks' teeth are made from the same material as ours: enamel and bone. They are also dark, shiny and have jagged, tooth-like points that distinguish them from most shell fragments.
But they can be hard to find. The students spent about two hours collecting 10 gallons of sand and shell fragments at Bayfront, a beach about half the size of a football field.
Then they sifted out about three ounces of shark teeth.
As most of the group settled down to lunch, Cody Jameson, 12, kept digging along the waterline, where waves gently lapped against the sand. He wants to be a professional marine biologist, and he quickly demonstrated what he had learned about shark tooth identification.
"It has a certain design to it. It's skinny, shaped like a triangle and has a sharp edge," he said.
Will the cliffs ever run out of shark teeth? Not anytime soon.
Sharks have existed for 400 million years and each sheds thousands of teeth during its lifetime, making for an abundant - and diverse - supply along Calvert's shores, said Stephen J. Godfrey, curator of paleontology at the Calvert Marine Museum.
On Bayfront Beach alone, there are fossils from five to 10 prehistoric types of shark, including tiger, angel, sand and the most common find, gray sharks. Occasionally, a lucky fossil hunter will find the tooth of a snaggletooth shark, which grew to 15 feet.
"There are a lot of people who collect at a lot of places, but this is a premier place to find shark teeth," Godfrey said.
Calvert Cliffs is made up of three distinct geologic formations, known as the Calvert, Choptank and St. Marys formations, and the age of a fossil can be determined by where it is found.
Bayfront Park, in Chesapeake Beach, is part of the Calvert formation, which is the most northern and contains the oldest sediments, so that teeth found here are from sharks that lived about 18 million years ago, Godfrey said.
Sediments to the south, including the cliffs around the Calvert Cliffs Nuclear Plant and the nearby state park, contain much younger fossils.
Most of the land along the cliffs is privately owned, but fossil hunters can reach the shoreline at different parks and public sites.
"We get an awful lot of college students," said Connie Smith, who has operated Matoaka Beach Cabins in St. Leonard with her husband for 47 years. The couple rents cottages for overnight stays and allows shoreline access to day-trippers.
Fossils embedded in the cliffs belong to the property's owner, but fossil hunters may keep anything near the water's edge, said James P. Reger, chief of environmental geology for the Maryland Geological Survey.
Visitors also should stay off the cliffs. "Its not safe to try to dig something out of the cliffs. They're fairly unstable," Reger said.
The right weather is important, too: Look for strong westerly winds and conditions that blow water out of the bay, lowering the water line near the cliffs.
"If I had to pick a time, it would be after a really big storm," Reger said.
A new moon and a full moon also help, because the tides pull more of the sea away from the shore, says Hazen. Then it's a matter of initiative.
"What you want is to be the first one out on the beach. If you're not, someone else is going to find whatever is there," he said.
Hazen didn't come to Calvert County to collect fossils. He and his wife, who live in Bethesda during the week, were attracted by the waterfront scenery when they bought their house in Port Republic about 15 years ago. But things changed one day during a walk on the beach.
"I saw people bending over and picking things up, and I asked them what they were doing and they said, 'Looking for fossils from sharks' teeth.' I had been collecting fossils all over the world, so I figured, 'Why not here?'" he said.
Hazen, whose 20th publication, a book about evolution, is due out in 2008, has hunted fossils since he was a teenager. His collection of 2,000 trilobites, a widely studied ancestor of the horseshoe crab, has taken him to Africa, Europe and Australia.
He's donating that collection - reputedly the world's largest - to the Smithsonian Institution, where dozens of specimens are expected to be displayed in a new Hall of Oceans exhibit in the Museum of Natural History in 2008.
"It's unbelievable stuff. It's just gorgeous material, I'm almost afraid to touch it," said Bohaska, the Smithsonian paleontologist.
But a highlight of Hazen's years of collecting came in January 2000 when he and his wife, Margee, each found fist-size teeth from an extinct variety of great white shark. They're displayed on a shelf in his house, along with corals, barnacles and two vertebra from a baleen whale that was probably 12 to 15 feet long.
"The idea that you can walk out of your house and find a 15 million-year-old whale bone is fascinating," he said.
His collection from Calvert Cliffs doesn't bear directly on most of his research at Carnegie. But it helps define his perspective on the complexities of evolution and life's origins.
Besides, it's a lot of fun.
On a recent fossil hunting walk near his house, Hazen used a half-broken rake to comb through the sand and debris at the water's edge. He quickly uncovered a tiny tooth from an extinct form of tiger shark - galeocerdo contortus. That was just the beginning.
"Here we go," he said, picking up what looked like a slab of petrified wood. He thinks it's a whale bone, about 15 million years old, but he'll ask Godfrey for his opinion later.
Another 10 minutes of walking led to the day's biggest prize: a tooth about 2 inches long from an ancient mako shark. He estimated the mako's size at 15 feet.
"This is big enough that this would have been eating dolphins," Hazen said.
During the rest of the hourlong walk, he seldom lifted his eyes from the sand. "There's a lot of things to look at, and you never know what you're going to see," he said.