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NEAL CONAN, host: This is TALK OF THE NATION. I'm Neal Conan broadcasting today from the headquarters of National Geographic in Washington, D.C. Constanza Ceruti's explorations take her to the tops of remote mountains, breathing blistering cold, sudden storms and whipping winds, all to study places nobody's visited for hundreds of years, ritual sites atop sacred mountains in the Andes.

She's a National Geographic emerging explorer and the world's only female high-altitude archeologist. She combines her Ph.D. in anthropology with expert mountaineering skills to study ancient people and their ceremonies.

While she's above the clouds, cultural ecologist Kenny Broad dives deep into the world's caves to explore freshwater reserves around the world and study effects of climate change. He says he's never turned down a diving job. I guess that helps. He studies how the world can sustain fresh water longer in the classroom too, and is a documentary filmmaker.

We want to hear from explorers today. Call and tell us why you do it and how far you push it. Our number is 800-989-8255. Email us, talk@npr.org. You can also join the conversation at our website. That's at npr.org, and click on TALK OF THE NATION.

We're also going to take questions from people here in the audience at the Grosvenor Auditorium, and welcome to all of you.

(SOUNDBITE OF APPLAUSE)

CONAN: Later in the program, National Geographic cartographer Juan Jose Valdez on his new map of his native Cuba. But first we're joined onstage by National Geographic explorers Constanza Ceruti and Kenny Broad, and thanks for both of you to come in, it's nice of you.

KENNY BROAD: Thank you.

CONSTANZA CERUTI: Thank you.

CONAN: Kenny Broad, do you go down in caves because - to find stuff out or because it's fun?

BROAD: I'm actually in the witness protection plan.

(SOUNDBITE OF LAUGHTER)

BROAD: And I wasn't going to reveal it, but the statute of limitations is up. No, I got to caves via the water, where - when was I was a little kid, all I wanted to do was dive, all I wanted to do was get in the water. And I guess the ultimate, the Ph.D. for diving is cave diving. And at the bottom of dry caves tends to be water where it collects, and that's where it tends to stop people. So if you can dive into that, you can have an edge on the - what's around the corner.

CONAN: And why dive to find stuff out? The bottoms of the oceans can be explored by robots.

BROAD: Yeah, I mean the good thing about cave diving is we can now compete with technology. There's - you can't send a manned or unmanned submersible into caves. There's just not the intelligence there and the computer decision-making to find its way through kind of complex mazes. There's not the dexterity to take the samples. There's not the judgment and decision-making to be able to decide on the fly what direction to go, you know, where is too far.

And it would get too expensive, and you can't go very far with these tethered machines.

CONAN: Sometimes you do go too far, though. Small cracks, you have to take off your equipment, wriggle through.

BROAD: Yeah, I mean, we - when you tell people that you work in a small, dark place with no oxygen, you tend to think of the most dreadful situations of the cave-ins, of the - getting lost, getting stuck. But that's not - it tends to be the little things that get you. It's walking to the dive site where you fall down.

(SOUNDBITE OF LAUGHTER)

BROAD: But there's plenty of risks, but we tend to overweigh some of the dreadful, dramatic ones, and we don't even think about the routine ones, and it's the routine, the things you do all the time, that are probably the most dangerous.

CONAN: Constanza Ceruti, in Kenny's case, he found the water first, and then I guess the science. Which comes first, archeology to you or mountaineering?

CERUTI: First comes archaeology and anthropology, as I am born and raised in a city in Argentina with no mountains. But ever since I met the mountains, they came into my life, I wanted to be an archeologist who could work on high mountains. So the vocation was really from the very beginning.

As soon as I got rated as an anthropologist, I studied climbing out of the blue, up to 17,000 feet, and no, that's the bottom line, and yeah.

CONAN: And up, up to - well, I know that one of the mountains you've done some work on is about 2,000 feet taller than Denali, the highest mountain in North America.

CERUTI: Yes, it's about 22,200 feet high, and it's not only that we were reaching the summit, like most mountain climbers may be able to do with a lot of effort, but also we had to stay there for at least half a month doing archeological research on a mountaintop shrine built 500 years ago by the Incas.

CONAN: Does every mountain in the Andes, is every mountain sacred?

CERUTI: They are - yeah, most of them are sacred. Some of them were climbed by the Incas, who, by the way, are the first group in the history of mankind to go this high, above 20,000 feet, to make offerings and sacrifices. All of them are perceived as sacred. But in the Andes, it means that you, you know, you are drawn to get close to the mountain and be as close as possible.

CONAN: And do all of them have burial sites or ritual sites?

CERUTI: Oh, no, no, no, that's a very exceptional thing. The Incas would only send children, which they considered to be messengers to the gods, to the mountains that were more special to them. And how they defined that is what we are, you know, trying to learn about. But it's - this is a very exceptional thing.

Most of the time, the Incas would go so high, up to 20,000 feet, and just carry a bit of firewood and deposit that and make that be the offering. That's the usual thing we find up on the mountains.

CONAN: The offering to the gods.

CERUTI: Yeah, yeah.

CONAN: And have you ever, in the course of ascending to one of these places to see what you could find, have you ever said, this is crazy, I'm going to go back down?

CERUTI: It's well, of course we have that feeling always. But on the other hand, we are so aware that the archeological work is important because we are helping to preserve this heritage for future generations.

So we tend to kind of leave aside our own fears and try to, you know, keep going. But we are very respectful in the way we go to the mountains. So we always feel welcomed. And we (unintelligible) the mountains, and we have been very blessed in our climbs.

CONAN: We're talking to explorers today. You just heard from Constanza Ceruti. Also with us, Kenny Broad, the 2011 National Geographic Society Explorer of the Year. We have a question from here in the audience of the Grosvenor Auditorium.

UNIDENTIFIED MAN: Yeah, my question is for Constanza. I wanted to know what it's like for you, being a woman in a risky field that is so dominated by men, and by extension of it being so risky, I assume relatively manly men.

(SOUNDBITE OF LAUGHTER)

CERUTI: Yeah, well, I have to be...

BROAD: Relatively.

CERUTI: ...completely honest, I think those kind of issues are more likely to happen at sea level...

(SOUNDBITE OF LAUGHTER)

CERUTI: You know, back in the university or in the academic environments rather than on the mountains. And I have always felt very comfortable working on the mountains. I also have to be very honest that the ladies room is usually far, far, you know, far away.

(SOUNDBITE OF LAUGHTER)

CONAN: I guess it has to be. When you're on the mountain working for - a mountaineer doesn't go up - will go up a mountain like that, but they're not going to stay for a month or two.

CERUTI: That's why high-altitude archeologists, there's just a few of us in the world. And like Dr. Johan Reinhard, who is an explorer in residence here at the National Geography. It's very few people because most mountain climbers will enjoy going up, but then they don't want to stay, and most archeologists simply don't want to go up. They have the patience to do the work, but they won't be able to go to 20,000 feet.

CONAN: Let's get a caller involved in the conversation. We want to hear from explorers in the audience today. Why do you do it? How far do you push it? 800-989-8255. Email talk@npr.org. And we'll start with Todd(ph), and Todd's with us from Beaufort, South Carolina.

TODD: Correct. We actually pronounce it Beaufort, but close enough.

CONAN: Beaufort, all right, I apologize.

TODD: I teach at the high school level, and we had taken six-foot weather balloons, 1,200-gram(ph) weather balloons, attached a camera to it and let them go. And we've - they've reached over 100,000 feet. And the camera will take a picture every 10 seconds.

CONAN: And what do you find out?

TODD: You can see the curvature of the Earth. We live on the coast. You can see the coastline. You can see thunderheads. We thought we might have captured a little satellite one time, but we looked at the altitude and it was just a jet.

CONAN: And this is - what are you hoping to find?

TODD: Well, I teach photography, and it's just to get the kids excited about it. You know, there's so many people today that can't do anything, and the biggest reason is they're afraid to try.

CONAN: And have you inspired kids to go on to do other things?

TODD: We've had a - I've had a few kids go into photography, some of the Charleston colleges and take art classes and major in that. And - but, you know, it's a good time. It's a lot of different disciplines. We track it with Ham Radio transmitters and commercial satellite trackers.

CONAN: And where do these balloons come down?

TODD: It depends on the time of the year. If you do it in the winter, they might come down 150, 200 miles away. If you do it in July, they might come down 25 miles away.

CONAN: And do you retrieve them?

TODD: Yes. We've found - we've lost five balloons. We've got all the balloons except the first one, and it came down in the middle of a dirt road, and we think someone found it before us. But we've retrieved every one of the others.

CONAN: Kenny Broad?

BROAD: Just to comment on what the caller is talking about, I mean, we often focus on exploration, where it's the individual taking some sort of physical risk. But there's a lot of exploration to be done, particularly in groups involving children, that we can bring a lot back to science, and we're learning things that we don't know with simple technologies combined - like balloons, but combined with an ability to get information out there in kind of a citizen science platform. So it's great to hear about these sorts of projects.

CONAN: Thanks very much for the call.

TODD: And there is a NASA competition for this, and I want to try to get a group together. We're going to try to enter the competition this year.

CONAN: Well, good luck to you.

TODD: Thank you, sir.

CONAN: Thank you, Todd. And it's important to point out, Constanza Ceruti, we point out the risks involved in high-altitude archeology. You also do a lot of your work at sea level in a laboratory.

CERUTI: Yes. We also do a lot of work in libraries on the university campus. On the mountains, we are going to be facing not only the climate conditions that can be very hard, like snowstorms, extremely strong winds, you know, the low temperatures and the fact that in Argentina, it's very difficult to get proper mountain equipment. So usually, we are underdressed for the conditions we are going to face.

And let alone that, we are always working in a hypoxic environment, meaning that there's very little oxygen available. So the body is exposed to high-mountain sickness to start with, and then eventually, it could lead to pulmonary edema or brain edema, which are very delicate conditions.

So we are always facing these kind of problems and trying to cope with them with our most respectful approach to mountains and trying to be aware of our own limitations.

CONAN: Do you bring oxygen with you?

CERUTI: No, we don't use any supplementary oxygen when we are up there, because we couldn't possibly climb the mountain as many times carrying the oxygen in addition to the food and the equipment to the archaeological work. So we have to get our bodies naturally adjusted to the altitude.

CONAN: So you take a while climbing the mountain.

CERUTI: Yes. We are our own porters, in a way - I mean, the team. So we go up and down with loads of food and equipment, and then eventually we camp on the top. And then we do the archaeological work.

CONAN: So, high-altitude archeologist and Sherpa.

CERUTI: Yes.

(SOUNDBITE OF LAUGHTER)

CONAN: All right. We're going to talk more with explorers Constanza Ceruti and Kenny Broad when we come back from a short break. We'd like to hear from explorers in the audience: 800-989-8255. Email us: talk@npr.org. Stay with us. I'm Neal Conan. It's the TALK OF THE NATION, from NPR News.

(SOUNDBITE OF MUSIC)

CONAN: This is TALK OF THE NATION, from NPR News. I'm Neal Conan, at National Geographic here in Washington, D.C. When we were here back in January, Robert Ballard, another explorer, told us the age of exploration is just beginning on our planet. In fact, he said, the next generation of kids will probably explore more of the Earth than all previous generations combined.

He was talking, of course, about the miles of underwater mountain ranges, volcanoes and caves that lie below the surface of the world's oceans. All that exploration will help us understand our world, but it also carries risks. We're talking today about the limits of modern exploration.

We want to hear from explorers today. Call and tell us why you do it and how far you push it: 800-989-8255. Email us: talk@npr.org. You can also join the conversation on our website. Go to npr.org. Click on TALK OF THE NATION.

Our guests are Kenny Broad, environmental anthropologist and cave-diver, named the 2011 National Geographic Society Explore of the Year, and Constanza Ceruti, high-altitude archaeologist who focuses on Andean people, the Incas, and a National Geographic explorer herself.

Let's go to the phone, and this is Michael, Michael with us from Dunedin in Florida.

MICHAEL: Yeah, good afternoon. Mr. Broad, congratulations on the (unintelligible) of the year award from the National Geographic. It's got to be quite outstanding. I'm a - I guess you could say an ex-cave diver. I dove back in the early '70s throughout Florida and reached my limits in the cave at Devil's Eye down here, got silted up. We didn't know how to swim properly back then, and got silted up pretty bad, and I panicked and backed out.

But my question really is, I've done some research for the state of Florida on offshore springs, and my question is, really: Is anybody following up on the possibility of ancient human habitat, you know, back beyond the Holocene Shoreline offshore and finding artifacts at some of these springs here - that are offshore?

CONAN: And explain the Holocene Shoreline, if you would.

MICHAEL: The Holocene Shoreline...

CONAN: No, no, I was going to ask Kenny to do it, but go ahead.

MICHAEL: Oh, I'm sorry, my apologies.

CONAN: That's okay.

BROAD: No, no. Go ahead. Well, first of all, thanks for the call, Michael, and congratulations actually on surviving diving in Devil's Eye in the '70s. That...

MICHAEL: It was an experience.

(SOUNDBITE OF LAUGHTER)

BROAD: Yeah, I mean, that was the epicenter for kind of the pioneers of cave diving. Cave diving evolved as an activity as kind of trial and error, and it had its evolutionary period - short and not sweet - with many deaths. And it's only the guidelines we have now for diving safely in caves that, you know, came from people like you, who took chances and either were lucky or sometimes not so lucky.

MICHAEL: (unintelligible)

BROAD: But to get to your question, if we go back to, you know, the Holocene period or periods, you know, let's say about 10,000 to 20,000 years ago, where those are some of the oldest remains in Florida, tend to be found in the underwater caves or sinkholes, because they're perfectly well-preserved if they're in anoxic or oxygen-free environment. And you don't find that on the low-lying land, especially because we've been scoured by hurricanes for hundreds of thousands of years.

But offshore in the coast is very difficult to work in, just from a time perspective. You don't have much time underwater. They've also been subject to lots of wave action.

But there are sinkholes offshore, and there are people starting to look at them and do some work in these sinkholes. And I think it - as our diving technologies get more advanced with rebreathers, we're able to spend a lot of time underwater with less of a decompression profile. So while rebreathers have their risks to them, they also give us a way to extend our exploration. And I think some of these offshore areas, particularly in Florida, are going to become real hotspots for exploration.

MICHAEL: Yeah. I was looking at them for water loss from the aquifer for the state of Florida, and I know there's a lot more out there than we've even discovered so far. But one other question, and I'll get off. I just want to make a mention of Wes Sykes - Skiles, who was lost to us last year, a great cave diver and fantastic photographer, a true loss to our - to your profession, I should say. But thank you very much for taking my call.

CONAN: Thanks, Michael.

BROAD: Thank you. And, yeah, Wes, who was a member of the National Geographic family, Wes Skiles, was also my personal mentor and one of my closest friends. And he's the one who kind of brought me into the cave-diving world.

CONAN: It is not just anoxic, underwater places without oxygen that preserve human artifacts and human remains. Constanza Ceruti, they're also preserved by altitude and cold.

CERUTI: Yes, the lack of oxygen or the low levels of oxygen in the mountains above 20,000 feet, plus the cold, can preserve. They combine to allow human bodies like those of these children that the Incas selected to send to the mountain gods as messengers to become what we know as the best preserved mummies in the world.

And so in this expedition that I was leading with Dr. Johan Reinhard, an exploration funded by the National Geographic in 1999, we were very fortunate during the excavations at the highest archaeological site in the world, on Volcano Llullaillaco, to find three mummies of children, six, seven and 15 years old, that are considered to be the best-preserved in the world.

All the organs are in very good condition. We could study them through CT scans, do DNA analysis, reconstruct their diets through hair analysis and always study them in a very careful way in order to preserve. You know, we consider preservation, like, the most important thing. And that's why we decided that these children need to stay in a laboratory, especially given the conditions such as climate change and looting and treasure hunting that are going on in the Andes these days.

CONAN: A little bit more about the climate change: Some might say these should be left where they were placed all those hundreds of years ago, that it might be disrespectful, in some sense, to remove them from their graves.

CERUTI: They - what we consider, of course, all opinions are welcome and respected. But we do have to be aware that the conditions in general have changed, and we're no longer in an environment like 500 years ago. And consequently, what we do when we are in an expedition, usually our collaborators are native or indigenous people. I myself am partly indigenous.

And we do all the ceremonies and rituals to ask for permission to the mountain before we go up, and then we do it in a such respectful way, and we really put all our hearts into it. Plus we - you know, our life is there in the hands of the mountain, as well, so to speak. So we are, you know, there fulfilling what we think is a unique mission, that if it's not done properly and right now, this is not something we can postpone for the future, unfortunately.

CONAN: You speak of the mountain as if it was sentient, as if it had thoughts.

CERUTI: Oh, well, that's how Andean people - I spent five years of my life in an indigenous community, and I learned really firsthand why sharing, going on mountain pilgrimages and making the offerings, how Andean people perceive mountains and landscape in general as a living entity.

And we have so much to learn from them and from, you know, indigenous and native people worldwide because they see - they tend to see the mountains under this light, and it's such a rich way - or how can I say - such a touching way to perceive landscape, not just as a resource, but as a place where we can communicate at the spiritual level. I think that's very precious.

CONAN: Here's an email from Sara: There are elevations above which we are told human bodies steadily deteriorate. You work at 20,000 feet. At what elevation do you usually set your camps? Does there seem to be a limit on how long your body will let you stay that high?

CERUTI: Well, this is really - there are differences in each human person. I mean, the human body will react differently to the elevations. I personally was staying for almost a month at 19,000 feet, and I did not experience any deterioration in particular.

I actually put on weight, which is quite, quite strange, whereas as when we were on Mount Llullaillaco and those 15 days at 22,000 feet, 22,200 feet, you can lose some of your body, especially the muscles in the body. You're probably going to lose a lot of muscles because that's where (unintelligible) comes from that the body needs when you're in the elevation. No matter what you're eating, it probably is going to happen.

Otherwise, you can have some, you know, long-term brain damage. I hope it's not the case here.

(SOUNDBITE OF LAUGHTER)

CERUTI: And you never know until you go back home whether you have been exposed to frostbite or other conditions. I have had a few of the mild conditions like frostbite in my finger and my toes, having all the blisters, you know, coming down from Aconcagua, the highest mountain the Western Hemisphere, finding all my hands full of blisters.

But fortunately, I keep my fingers and my toes, and I think it's because we, you know, we really are very respectful towards the mountain. We don't need to conquer the mountain at all. We just want to commune - be in communion with the mountain.

CONAN: We have a question here in the audience at the Grosvenor Auditorium.

UNIDENTIFIED WOMAN: Hi, thank you. This is question for both of you. I'm just an enthusiast and traveler myself. So I was wondering, of all of your travels and explorations, where is your favorite place on Earth, either above sea level or below?

CONAN: Present company excepted, of course, National Geographic headquarters dear to both of our guests. Kenny Broad, why don't you go first?

BROAD: You know, it's usually the last place I was, and just because it was probably the most lasting impression on my brain. If I had to get abandoned somewhere for the rest of my life, where would it be? Wow.

(SOUNDBITE OF LAUGHTER)

BROAD: I've never posed that. It was, you know, I love Florida and I love the Bahamas. It has to be warm. I will never run away with Constanza to the mountains.

(SOUNDBITE OF LAUGHTER)

CONAN: Constanza.

CERUTI: I may be, you know, going towards the sea because I'm enjoying snorkeling more and more. I think it has a spiritual dimension to it. I would, you know, try a more philosophical reply because it's so difficult. I mean, you have seen so many wonderful places in the world to choose one. So I can say each one of them, or I can say right now, because present shall always be the perfect place to be, so we can try that.

CONAN: Here's an email from Jessica in the Sawtooth Mountains in Idaho: I've never been a thrill seeker. In fact, often in my adventures, I've told my comrades, just because it's more dangerous doesn't make it more fun. However, I thoroughly appreciate exploring areas that aren't easily accessible, aren't comfortable places. These experiences remind me that I'm alive and keep me from going through life as if it's a merely a humdrum occasion and not something fantastic I should constantly appreciate. Kenny Broad, I wonder if you have some thoughts on that.

BROAD: Yeah. I think we often confuse thrill seeking with exploration. And most of the people that I know who do things that are admittedly high risk, they're very, very meticulous risk managers. It's about keeping your adrenalin down, not letting it get up. I mean, they also have a healthy dose of cognitive dissonance, where I think they're in, you know, a certain degree of denial because you don't want to be overcome with the emotions that you get from, maybe, bungee jumping or those sorts of activities, which I personally would never do and scare me.

CONAN: Constanza, I wonder, though, have you ever found yourself on a mountain after making a discovery as astonishing as the ones you have made and finding yourself so distracted by your intellectual interest that you forget you're standing on top of the mountain that you can fall 20,000 feet?

CERUTI: Yes. Of course, it does happen just like that. When we are working on the, you know, we are aware that we have to do the archaeological work as good as possible. We are too focused. And we sometimes actually lose the joy of being on top of the mountain, which we recover when we are on glacier mountains that don't have archaeological sites from the summit and we were there just to enjoy. But on the other hand, the climbing is such a powerful, emotional experience that sometimes it's nice to be able to be, you know, using your brain while you're up there. It's kind of - otherwise, it will be just slow moving. I don't know, I think it's getting difficult to explain.

CONAN: Constanza Ceruti and Kenny Broad, both National Geographic explorers. You're listening to TALK OF THE NATION from NPR News. And let's go next to Fred, and Fred is with us from Lansing in Michigan.

FRED: Hi. Thanks for taking my call. I'm calling about getting people with disabilities - in my case, blindness - into various levels of exploration. I've been running a science camp for the past three summers in - near Greenville, Michigan. And your call screener was asking me, do we go long ways away. I said, one of the things that we're concentrating on is helping people to understand that you can start exploration, and I've come to realize, right in your own backyard. You don't even have to go off your block.

But the call scanner asked me about safety and I - he said, well, do you take all kinds of safety precautions? And I said, no, just the opposite. I mean, well, in a way, we're very safe. It's like you said we're careful, but we try to push our kids beyond what - because everybody, just like your call screener, is always concerned that blind people need some kind of special protection or something. And we want to help kids counter that so that they can learn to love exploration and science.

My brother is totally blind. He is the first blind person to ski all the way across Lapland on a National Geographic expedition. And I'm trying to help other young blind kids now start to believe in themselves. And it was interesting to me, last summer, that the most challenging part - they didn't have any trouble in the science labs and on the city streets and even in the farm fields where we went. But we went walking up a stream, which is a very calm stream - it wasn't a rapids or anything - and sinking in the mud and experiencing the - all the things that you feel as you're walking up a kind of a silty bottom stream - that was probably the most challenging thing to them. So I'm really hopeful - I don't know if you've ever had Geerat Vermeij on your program or not, but he wrote - he's a MacArthur fellow who's blind and studies seashells. It might be really interesting for him to be on your program sometime.

CONAN: Thank you for the suggestion. As the - what kind of science do you do with the science camp?

FRED: What we're trying to do now is general, a kind of a general approach. So we try to get a little chemistry, a little earth science, a little biology, some physics in there, to try to introduce because blind kids are, many times, excluded from science classes because of a misunderstanding of science teachers that don't understand how to include blind children in their science programs. So we're trying to get science teachers to join us so that we can teach them how to teach blind children. And we're trying to get the blind children to believe in themselves as potential scientists.

CONAN: Good luck with your project.

FRED: Thank you.

CONAN: Appreciate the phone call.

FRED: You're welcome. Thanks for...

CONAN: As you - have either of you been brought up short sometimes in your expectations of what an explorer is and who can do it?

BROAD: I definitely have. And in fact, it was my very first moment where I felt - internally, I had the hubris to say I was an explorer. And it was about 20 - 1989, and it was the first real expedition to the Bahamas, cave diving, an unknown area, that we had heard there were caves. And it was the first dive of the expedition, and I was alone and came up to the group that included my mentor, Wes Skiles, who we mentioned before. And I had never been prouder, and I just explored this cave, laid a bunch of guideline, came out.

It was about 3:00 in the morning because we were doing it with a certain tide. And I was - essentially just held up my diving reel empty, showing, look, I just explored a thousand feet of cave. And he said, let me see your survey slate. And I said, well, I didn't take any notes. And then he said, well, then you weren't there. And, you know, that kind of taught me a lesson right there that - or at least in my mind - that made the difference between going on an adventure and actually doing exploration.

CONAN: Kenny Broad. Also with us Constanza Ceruti. They are both now considered explorers by National Geographic, which is the stamp of authenticity, I think. We're going to talk more about the risks and rewards of exploration in just a moment. We're also going to be talking with the geographer. You'll find out who that is in just a moment. Stay with us. It's NPR News.

(SOUNDBITE OF MUSIC)

CONAN: Right now we're talking with explorers about what they do and how far they push it. Kenny Broad is the 2011 National Geographic Society Explorer of the Year. He's an environmental anthropologist and cave diver, also a documentary filmmaker. National Geographic explorer Constanza Ceruti is also with us, a high-altitude archaeologist who focuses on Andean people or the Incas. And I wanted to ask you, are accounts of the Incas - most of what we know comes from those who conquered them, the conquistadors. They wrote down what they knew about these people from their point of view. How do the Incas speak for themselves?

CERUTI: And that's one of the most rewarding things about high-altitude archaeology or Andean archaeology in general, when we can give a voice to these ancient civilizations. And we can - like in the case of the mummies we have found, the Llullaillaco children, when we studied them by hair analysis and we learned what they ate before they died, all these details are a way to allow them to tell their own story. So we're learning about Inca relation directly from the Incas, and I think that's absolutely special. And that's why, I think, science is a way to, you know, have a bridge to the past without all these biases.

I mean, we do use - we have historical sources from Spanish conquistadors, but we know what we are doing, and, fortunately, we have mummies that can speak if we can listen to them properly. And then we have this firsthand account. And, of course, ethnographic research is also important. So we do go with the Andean people (unintelligible), which is to the mountains today, and we learn from what they do and how they relate to the mountains. And that's, of course, another way to understand. That is most important, I suppose, and I really enjoy doing all this holistic research, not just technical archaeology.

CONAN: Earlier, Constanza Ceruti told us that one of the reasons the mummies have to be brought down from their graves in the mountains is because of climate change and the change in temperature as it grows warmer. And, Kenny Broad, I know climate change is among the things that you study at the other end of the spectrum, at least altitudinally(ph).

BROAD: Right, right. So as it turns out, there's a couple of places where you can reconstruct past climate quite well with samples. One of them is through ice cores, and the other is underwater caves and stalagmites. Those are those cave formations, limestone, that grow from the bottom. And you can cut them into a small, thin slab and look at them almost like a tree ring and do isotopic analysis and reconstruct with high resolution how quickly the climate changed in the past.

And from our recent Nat Geo expedition, we're finding evidence with the lab work at the University of Miami that climate has changed dramatically. So abrupt climate change within sometimes 20 to 50 years on a - that matches some of the global-scale changes. And these caves also record sea level rise. So there's also been periods of rapid sea level rise, so that these time capsules may give us a glimpse into what we're looking at in the future with global warming.

CONAN: Let's get a caller in. This is Peter, Peter with us from Pine Ridge in South Dakota.

PETER: Hi. My comment is related to the reason we take risk to do extreme science. I do research in Denali National Park in the summer, and then in Chile. And I study lichens. And these places are remote and hard to get to, and we spend lots of time in the backcountry in Alaska dealing with wild animals. And then in Chile we spend time around volcanoes studying the impacts of volcanic eruptions on forests. And it's where the good data is, in a lot of cases, is remote places. That was my first point. And the second was that when you're out there for so long and you get this lucid sense of how tenuous life's grasp is, you know, with these animals around any corner, it just - I don't know. It's a kind of a personal driver to keep you going. It really fuels your love for collecting the data.

CONAN: So you're the Willie Sutton of lichen? You go to the rainforest because that's where the money is?

PETER: Well, no. It's where the new species that haven't been discovered yet. It would be like going to the Amazon for lichens, in a way.

CONAN: Hmm. Constanza Ceruti, I think some of what he is saying...

COSTANZA CERUTI: It makes sense. I mean, first of all, I would love to showing him in Denali. So anytime, I will come visit. And the second is that on the mountains, lichens are the form of life that we are likely to find at the highest elevations. When we are climbing, we know that we are about 17,000 feet and then there's no grass, the grass line. You know, we have (unintelligible)...

CONAN: Oh, we know about the tree line. There's a grass line too?

CERUTI: And the grass line is around 17,000 feet in the Andes. And after that, all you may see is lichen up to 18,000 feet sometimes. And then after that, there's nothing. The occasional condor, maybe.

CONAN: A condor flying high above. Peter, thanks very much for the call.

PETER CALLER: Sure.

CONAN: One last question and this is from the audience here at the Grosvenor Auditorium.

AUDIENCE MEMBER: Hi. Yes. My questions are directed to both the participants. And I'm wondering whether or not it's a false assumption to think that the costs, whether time or financial or opportunity cost of developing the expertise, whether technical or academic, is a significant obstacle to modern-day exploration. And I guess how you guys got into that and what the challenges are for young people who have those same passions.

BROAD: I'll take a first shot at that. I mean, I don't think for someone who really - once they get bitten by the bug, I don't think money is as much the obstacle. It's, I think, exposing, particularly, young kids to the ability to explore, to let them, you know, get a sense of independence and wonder. And I think, you know, not to bash our educational system, but when there's - and I have two young boys who are here in the audience - but there's a lot of teaching for the test as opposed to letting kids explore and find things on their own. And I think, you know, I see it more as the way we give freedom to our young kids as opposed to, you know, kind of the structural limitations.

CONAN: Constanza Ceruti?

CERUTI: Well, when it comes to, like, your academic studies, we are blessed in Argentina that we can go to university for free. I mean, that's really special. And then we feel, of course, the moral obligation to give back and to become professors like I am at the Catholic University of Salta. So in that sense, I can give a personal opinion. It has not been difficult from that standpoint. And I did my best as a student. I think, mostly, you need two things to be an explorer which, gladly, all human beings have: A heart and a brain. And the heart will help you choose what you want to explore, and the brain will help you choose how to explore it, so...

CONAN: Thank you, both, very much. We appreciate it.

(SOUNDBITE OF APPLAUSE)

CONAN: You've just heard Constanza Ceruti, a National Geographic emerging explorer. Also with us, Kenny Broad, the director of the Abess Center for Ecosystem Science and Policy at the University of Miami. And thanks very much for joining us today.

BROAD: Thank you.

CERUTI: Thank you.

CONAN: We'll talk with the geographer in just a moment.

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