英語聽力：自然百科 考古揭秘佛羅里達州

The cool waters of Wakulla Springs makes it a popular place to beat Florida's heat. Tourists lounge on the May beach, while the locals prefer the opposite bank. Despite the cold-blooded company, people have visited these historic springs for years. But for how long is a mystery archeologists hope to solve.

National Geographic Grantee Jim Dunbar and his research team are searching for signs of the first Floridians, Ice Age people who may have come to Wakulla for a spring break over 10,000 years ago.

Your teeth could project yourself back into a time. You would see a Florida that would look like that a Serengeti in terms of the animal population it had. And where would animals go like that? They would come around, maybe oasis where there was plentiful water resources and with, say, large herbivores that come in，what else would come in? The predators. It could be a sabre-teeth cat. It could be something like that, or it could be people.

The crew is hoping to hit Pader, prehistoric tools left behind by an Ice Age hunter. In the search for Stone Age tools, digging is done, the old fashioned way. Each bucketful gets carefully screened for the smallest clues. And the sand itself is helping geologists unlock the age of their discoveries. Quartz crystals in the sand naturally emit a radioactive signal that getsreset when exposed to light. By testing the signal, geologist Jack Rink can tell how long ago this sand layer was buried. Jack takes a core sample to study in his lab, and gets a reading on radiation levels.

“In a couple of months, we'll know how long it's been since this sand was last exposed to light. And by relating that information, we can say that the artifact was deposited at the same time as when the sand was exposed to light. And that gives us a date on the artifact itself.”

Part way through the dig, the archeologists have found hundreds of small artifacts, mostly smallflakes from stone hunting tools.

A short distance away, clues begin to surface as to what was on the prehistoric dinner table. A dive team led by underwater archeologists Andy Helmins sets out to investigate fossilized mastodon bones at the bottom of the springs. It's forensic science at 25 feet deep.

While routine takes notes, Andy makes a fascinating find, deep grooves on a mastodon fossil. It could be the work of an Ice Age hunter. While the divers explore underwater, geologists Tom Scott and Hurling Linz are heading out on a different expedition.

This one is underground with the help of special ground penetrating radar. They may look like Ghost Busters, but this gear really works. The radar reveals dense objects such as fossils buried below.

“So, you know, conceivably, we have the ground truth of this to see if this were a bone or some archeological material, but anyone of those little reflections done in the thermal camera are certain could be.”

Back at the dig site, Jim's team strikes gold.

“Below in the holes, right in this location, we found a tool that we believe, I would call it a benchmark.”

A well-preserved knife. Jim guesses that this point could be 14,000 years old, more than 1,500 years before people were thought to have arrived in Florida. It will take months for test results to reveal whether the tool belonged to one of the first Floridians. In the mean time, Jim and his team will just have to wait. Fortunately for them, Wakulla Springs isn't such a bad place to pass the time.

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