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Archaeologists are often thought of in that Indiana Jones kind of way - you know, flying off to remote ruins in search of mysterious treasures. But a lot of new archaeology isn't about objects at all - it's about ancient environments. One thing scientists are finding that even hunter-gatherers changed their environment.

NPR's Christopher Joyce has this story about how they altered North America's coastlines.

CHRISTOPHER JOYCE: Torben Rick has the kind of earnest enthusiasm for archaeology that you have to have if you're going to spend months digging in the dirt for fish bones and scallop shells. And he is duly proud when he finds something interesting.

Dr. TORBEN RICK (Archaeologist): What I've got here are a couple - I'll open the bag…

(Soundbite of paper bag crunching)

Mr. RICK: …these are red abalones.

JOYCE: They're big pinkish shells that Rick found on San Miguel Island in California and now keeps at his sunny laboratory at the Smithsonian Institution in Washington, D.C. For Rick, these palm-sized shells are 6500-year-old clues to help answer a big question.

Dr. RICK: How did people impact the environments in which they lived? And specifically, how did hunter-gatherers influence the animals and the plants and all those things that flourish in these ecosystems?

JOYCE: It used to be a common notion that hunter-gatherers lived pretty much in harmony with nature. They didn't change the land the way agriculture eventually would, they just adapted. Then scientists discovered a different picture. For example, they discovered that it was a hungry roving population of early humans that exterminated the big Ice Age animals: the mammoths and giant sloths, and cave bears.

Hunter-gatherers also started huge fires that changed the landscapes to make it better for hunting. Torben Rick says there's now evidence that early cultures also modified North America's coastlines thousands of years ago. That's where the abalone shells come in. When early Americans on California's islands dumped shells and other refuse, they unknowingly became dune-builders.

Dr. RICK: So there might have been a five-foot dune there at one time right above the beach. And a group of hunter-gatherers came in, lived on top of that dune, dumped their refuse there and left. And this creates a pavement that anchors that sand.

JOYCE: Small dunes eventually became big ones, built up like a layer cake, with trash dividing each layer.

Then there were intentional changes that people made, like the clam gardens in the Pacific Northwest. People built rock walls into the ocean shallows.

Dr. RICK: And what these rock walls do, and they're clearly human made, is they create behind them an area of sandy substrate that's really good for clams. You can kind of think of them like a terraced garden.

JOYCE: Rick has also found layers of sea otter bones thousands of years old in California's Channel Islands. The layers above just had sea urchin remains. He thinks people killed the otters because they ate too many shellfish. Since otters also prey on sea urchins, the urchin population then exploded. All those urchins ate up the underwater kelp forests, creating, what Rick calls, an urchin barren. Rick says intentionally or not, hunter-gatherers altered the environment for a long, long time, long before agriculture emerged.

University of Nebraska anthropologist Raymond Hames, who studies how people interact with their environment, says they had no choice.

Dr. RAYMOND HAMES (Anthropologist, University of Nebraska): The take-home point to some extent is that humans do things to make their life easier. It was really hard to make a living back then. So, you know, you took advantage of the knowledge and skills you had in order to make the environment useful to you.

JOYCE: Hames says sometimes in early human history, changing the environment led to disaster.

Dr. HAMES: The problem is that your successes lead to population growth, which then leads to more pressure on the system to produce more resources. Your successes can set you up for even greater failures.

JOYCE: Many archaeologists argue that societies, like the Easter Islanders and the Mayans, suffered after over-exploiting their forests and land.

Torben Rick notes that human activity is threatening places like the Everglades and the Chesapeake Bay now. Scientists are trying to restore them, but to what condition? He says archaeology can provide snapshots of what these places looked like at different moments in time, and how much people had altered them.

Dr. RICK: Well, here's a picture of 500 years ago. Here's a picture of a thousand, 2,000, 3,000, and you can put those together and come up with a much more concrete picture of how that ecosystems looks, how it changes, how dynamic it is and where we can expect it to go.

JOYCE: Rick's research on coastal exploitation appears in the journal "Science."

Christopher Joyce, NPR News.

HANSEN: You're listening to WEEKEND EDITION from NPR News.

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