Mystery of Easter Island

PBS Airdate: November 7, 2012

NARRATOR: It is one of the most remote places on Earth, an island shrouded in mystery. For centuries, people have marveled at these giant stone statues that dot the windswept terrain of Easter Island. Who carved these statues and why? How did they carve them? And, perhaps even more remarkable, how could they move statues that could be 32 feet tall and weigh close to 82 tons?

Now, a new experiment tests a theory for how the statues were moved…

CARL LIPO (Archaeologist): Okay, ready? Pull. Release. Pull. Release.

NARRATOR: …and attempts to find out how it was really done.

SERGIO RAPU HAOA (Archaeologist): The transportation of these statues is perhaps the most important contribution of this culture to humanity.

NARRATOR: Can just 26 people, using only ropes, move a 10-foot-tall, five-ton statue?

CARL LIPO: I think we can do it. I think we have the force, we have the manpower.

NARRATOR: Will this experiment help solve the Mystery of Easter Island? Right now, on this NOVA/National Geographic Special.

In the middle of the South Pacific, over a thousand miles from land, a tiny island emerges from the sea. Hundreds of years ago, Polynesian explorers discovered this place and settled here: Easter Island, also known as Rapa Nui.

What happened on this island, after they arrived, has intrigued archaeologists for centuries. We know the islanders carved close to 1,000 massive stone figures, instilled with the spirits of their ancestors. We know they moved them, possibly as far as 12 miles, and placed them on sacred platforms called "ahu." But we don't know how they did it.

According to island lore, the statues, called "moai," had simply walked into place. But how could a people who had no metal tools carve such imposing figures? How could prehistoric farmers, who didn't have the wheel, move enormous statues, up to 30 feet tall and weighing close to 82 tons?

SERGIO RAPU HAOA: Transportation of the moai on Easter Island is perhaps one of the most important archaeological problems that we have. It's the biggest mystery.

NARRATOR: Sergio Rapu was born and raised on Rapa Nui and served as governor for six years. Also an archaeologist, he's long championed the idea that the statues were moved in an upright position.

SERGIO RAPU HAOA: It is up to us to build a hypothesis and go after looking for the attributes on the statues that allow an explanation that they were moved vertically.

NARRATOR: Archaeologists Terry Hunt and Carl Lipo are heavily influenced by Sergio Rapu's theory. The key to proving it, they hope, is inside this box.

CARL LIPO: Here it is. It's a huge crate.

TERRY HUNT (Archaeologist): Oh, no. This is going to be sort of scary, to see it come out of there. It's so enormous.

Wow. I don't know if I'm going to feel better or worse when I see it, because the box is big, and we're going to move it with a small number of people.

CARL LIPO: Holy cow!

TERRY HUNT: Oh, my god.

CARL LIPO: Wow. That is amazing, the perfect replica.

TERRY HUNT: You know what? This is making me feel sick to my stomach.

NARRATOR: This precise replica of a moai is the centerpiece of a simple, but radical experiment being conducted, in Hawaii, by Lipo and Hunt. Over the next two days, working with a small group of volunteers, they will attempt to move this statue by walking it upright.

TERRY HUNT: When people ask, "How did your ancestors move the statues?" the answer was always, "They walked." And for the Rapa Nui, that was the answer. And for the foreigners asking the question, they thought, "Oh, that's silly," you know. "How crazy."

CARL LIPO: What we're trying to do is evaluate our ideas, our ability to explain how they were moved, why the archaeological record looks like it does.

TERRY HUNT: What we're going to do is tricky, and, it could easily not work. And we've never done this before. Rapa Nui people had centuries to figure this out and lots of people involved.

NARRATOR: To conduct this experiment, Lipo and Hunt will have just two days and 26 volunteers.

The statue tradition was brought by voyagers from Polynesia to Rapa Nui. Throughout Polynesia, carved wooden and stone figures are common, but no other island can compare with the size or number of statues found here. According to oral tradition, the moai were carved to represent the spirit of the islanders' ancestors.

SERGIO RAPU HAOA: The statues are the living face of our ancestors. In order to look living, you have to put the inlaid eyes on the statues.

NARRATOR: Some statues are topped with a red stone hat, or a topknot, called a "pukao."

The moai were cut from volcanic tuff, a porous stone made from compressed ash. Almost all of them were carved here, at Rano Raraku, a massive quarry, inside one of the island's three extinct volcanoes.

Littered around the site are statues in various stages of completion, some still emerging from the rock.

SERGIO RAPU HAOA: The most common way of carving the moai, here, is to carve around the face and the body, like awakening the statues from the rock.

NARRATOR: To do this, carvers used very dense stone tools made of basalt, like this one, used by modern day carver, Umi Kai, in Hawaii.

UMI KAI (Artisan): What we're trying to do here is cut a design that we want to follow, into the tuff.

NARRATOR: Umi Kai is using a replica of the same ancient tool, called a "toki," to carve a small version of a moai eye socket into volcanic tuff.

UMI KAI: If I was to do this using a modern tool, it would probably take maybe 45 minutes to an hour. This will take maybe a whole day to two days.

SERGIO RAPU HAOA: It would probably take a team of 12 people a year to produce a moai of this size.

Once the moais are completely carved, the back would still be attached to the mother rock with a keel. Eventually that keel will be perforated and some loose rock will be added under the back of the moai, so it remain floating as they cut off and release it from the mother rock.

After they finish carving, they slide it down, brace it at the foot of the hill, then finish carving the back.

NARRATOR: At this stage, the moai was ready to be moved to a sacred platform called an ahu, known to be a place of religious ritual.

TERRY HUNT: There has been lots of speculation about how the statues were moved, from crazy theories that they were shot out of volcanoes, to "aliens moved them." But in modern research, there's been a whole family of ideas about using contraptions, using palm logs for tripods, or sleds or rollers.

NARRATOR: According to several of these theories, the islanders used logs to move the moai.

The most recent attempt was featured in a NOVA documentary that aired in 2000, when archaeologists tried using a wooden sled to move a moai along wooden rails. It's similar to a method Polynesians used to move ancient canoes out of the water.

Ultimately, the method worked, and it gained wide acceptance, but not everyone believes that logs were used to move statues.

TERRY HUNT: The problem with these theories is that they have not drawn on the evidence we see on the moai, the statues themselves, on the roads.

NARRATOR: As they investigated the statues and the roads, they began to accumulate clues that they think will tell a different story. Building on another researcher's data and using satellite imagery, Hunt and Lipo have surveyed almost 20 miles of ancient roads.

TERRY HUNT: There are several roads that begin at the statue quarry of Raraku and go along the south coast; some go north; some go across the center of the island. These roads were used to move moai to every corner of the island.

NARRATOR: They think the network of roads may have been even larger, but the degraded road beds can be hard to find with the naked eye. So they are testing a drone equipped with a camera that will give them more precise observations.

Three, two, one, go. Wow!

CARL LIPO: We have satellite image coverage for the entire island, and we can see certain kinds of features. This gives us a way of integrating that at a level where we get incredible detail.

NARRATOR: The drone may help identify new roads, which can then be ground-truthed with modern surveying equipment.

Hunt and Lipo believe a crucial clue to how the statues were moved may lie in the slope of the roads, which they have measured, confirming the results of an earlier team.

CARL LIPO: What we've found is that the roads generally have a maximum of a three-degree rise as they go uphill, and then a maximum of about six-degrees when they go downhill.

NARRATOR: The island is fairly hilly, and the inhabitants understood that to move the statues, the roads would have to be leveled so they had a consistent and fairly gentle grade.

But how did they move them?

To find out, Hunt and Lipo studied more than 50 statues that fell, apparently while being moved.

TERRY HUNT: We noticed that the statues that were headed uphill, away from the quarry, had fallen on their back, most frequently. We also found that when statues were heading downhill, they'd fallen on their face. Statues on flat ground were kind of 50/50, and we could see that there was a pattern here.

We tested it, statistically, and realized that we had very clear indications that the statues were moved in the standing position. There was really no other way to explain that.

NARRATOR: This idea has the virtue of being consistent with oral tradition. In fact, the Rapa Nui language even has a word, "neke-neke," which translates as "walking with no legs."

SERGIO RAPU HAOA: For centuries, we have known that the moai did walk, as our ancestors said, but how exactly they did the walking is what we, the archaeologists, are looking into.

NARRATOR: In the 1980s, a Czech engineer, named Pavel Pavel, tried walking a statue, but met with difficulties.

TERRY HUNT: This is the statue Pavel Pavel tried to move, in 1986, with his experiments, moving the statues in an upright position.

CARL LIPO: By shuffling it across the surface, there was a lot of friction on the base, and as he did it, in fact, there was damage done to the base that removed material right down from the bottom here.

We thought this can't really be quite right, because the shuffling and the grinding isn't consistent with what we saw in the statue. So, on the one hand, we were, like, yes, they were moved standing up, but not exactly that way.

NARRATOR: To figure out a less destructive way to move them, they built on observations first made by Sergio Rapu, identifying differences between statues that made it to the platform and those that fell on the way.

On the more than 50 fallen statues they analyzed, what researchers call "road moai," the eyes hadn't been carved yet. They were left as sharp, angled slots.

According to Hunt and Lipo's measurements, road moai were chunkier: their bases were bigger; their centers of gravity were lower; kind of like a bowling pin.

Most of the road moai had a D-shape base, and the base was angled, so the statue leaned forward.

These were key features to Lipo and Hunt.

CARL LIPO: The statues were rolled across the front edge. And that front edge has a characteristic shape, especially as the statues get larger, that allowed that to happen.

NARRATOR: The statues that made it to the ahu platform show the difference. The eyes had been carved. Their sides had been trimmed, and their center of gravity shifted back and up. They'd been cut so that their bases were no longer angled, but flat. They leaned forward, but not as far as road moai. They stood more upright, and they'd lost a little weight.

Based on all these differences, the difficulties faced by the Czech engineer, Pavel, are understandable.

TERRY HUNT: Pavel was using a statue that had already been reshaped for a platform.

NARRATOR: The eyes had already been carved, it didn't lean as far forward, and its sides had been trimmed.

CARL LIPO: Ultimately, the evidence of how the statues were moved can be found on the statues themselves. They were engineered to move. The details of the statues were telling us about transport.

NARRATOR: But the only way to prove the statues walked is to test the theory. To do that, they'd need to make a replica moai, the most precise replica ever made.

They collect data embedded in thousands of photos of two fallen moai, one that fell on its back and the other on its front, and enter it into 3D modeling software.

Industrial Designer Max Beach then translates the measurements into data, which is used to make a mold for the statue. Their photos depict an 18-foot-tall, 19-ton moai.

Because of safety concerns and cost, they scale the replica down. Their statue will be 10 feet tall and weigh five tons, about the average of the nearly 1,000 moai on the island.

Hunt and Lipo nicknamed the statue Hotu Iti, as a tribute to Easter Island's legendary first ruler.

Max Beach is also creating an animation showing how Hotu Iti might move.

MAX BEACH (Industrial Designer): Carl and I started with a small scale model, to move it around on a table, to get an idea of, how would this thing walk back and forth? We felt there were some challenges with scaling this up, so we built a five-foot model out of wood that would allow us to see what some of the dynamics involved are, as this model scaled up.

NARRATOR: While this contraption doesn't look like a moai, the same principles of design and physics are still in play, like an accurate center of gravity and the rounded forward edge.

CARL LIPO: It has enough of the features that gives us a sense, when we pull it, that it's going to behave something like we expect with the large statue.

See if you can get it up high enough so that it starts to fall. You're, kind of, pulling it on the side, but also pulling it so that it wants to rotate.

TERRY HUNT: Bringing that center of gravity back over the…

CARL LIPO: Yeah. That's the point where coordination is key.

TERRY HUNT: Yeah.

CARL LIPO: There you go. That was a good step.

TERRY HUNT: Yeah, yeah. Beautiful.

NARRATOR: In addition to understanding the physics of how the statue should move, figuring out where to tie the ropes is going to be critical in making the experiment with the larger replica moai a success.

TERRY HUNT: The trick is to pull it in the right direction, with the right force, at the right time that it rocks forward on the forward edge, which has that rounded, that D shape.

NARRATOR: But will Hunt and Lipo's 10-foot tall replica moai behave the same way?

Wow, did it fall forward?

JAMES DIEDESCH (Design Engineer): We are going to stay true to the original center of gravity.

NARRATOR: Engineer James Diedesch is designing the mold for Hotu Iti, paying special attention to the center of gravity and how the statue is balanced.

JAMES DIEDESCH: When I applied density to this model, it calculates the exact center of gravity and is saved in this system, right here in the center.

This is important, because if the center of gravity were off, it could alter the way that these things were moved. So, if the experiment is to determine that these could moved by walking them, then the center of gravity has to be at the same height as it was originally.

NARRATOR: The mold, itself, is comprised of four layers and made in two halves, split down the nose.

JAMES DIEDESCH: Hotu will come out of the machine with about plus- or minus-30,000ths of an inch accuracy, overall. This is incredible in comparison to any other re-creations that have been made that have been mostly glossed over and symmetrical. This is nearly exact replica of what you could find on Easter Island.

NARRATOR: After nine hours of machining time, each half of the mold is fitted with an internal rebar structure to support the massive weight of the statue.

JAMES DIEDESCH: When we are ready to pour the statue, we are going to fill this thing with nearly six tons of concrete.

RODNEY HALL (Concrete Specialist): What we'll see in this truck is the new high-tech mix that we've developed specifically for the moai statue. It's lighter in weight, higher in flowability. It's more sustainable.

If you look really close…see the little beads, the spheres.

NARRATOR: The beads are expanded polystyrene, a type of synthetic foam. Putting it in the mix adds volume without adding weight. That makes the statue closer in weight to a real moai of this size, made from volcanic tuff.

RODNEY HALL: We're burying him to equalize the hydraulic pressure from the outside, so it can't move.

NARRATOR: It took 10 days from the time the concrete was poured into Hotu Iti's mold to the time the five-ton, 10-foot-tall replica was carefully extracted from the ground.

RODNEY HALL: Trying to get this right and have him perform like the original Polynesians intended, that's what our mission is.

NARRATOR: There is a lot at stake in figuring out how the statues moved, because it may cast light on this island's troubled past. There are vastly different ideas about what happened here. The story told by the islanders speaks of different clans and prolonged warefare. Fractured skulls from skeletons found on the island seem to confirm that. What would have brought on this violence?

According to oral legends, different clans around the island competed to build more and ever-larger moai. Needing logs to move them, they cut down the island's lush forest to keep up with rivals. As the forest disappeared and resources grew scarce, the rivalry turned violent.

Some have described this as a case of ecocide: a culture, bent on overexploiting its resources, spirals into disaster. But is this a true picture of what happened here?

Easter Island once looked very different. Pollen evidence shows that 25 various species of trees and shrubs once grew here, and reveals a dramatic change as the island was deforested, something pollen expert John Flenley attributes to human activity.

JOHN FLENLEY (Pollen Analyst): Our pollen results were strongly indicating to us that people had destroyed the forest. In fact, it was the clearest example, in the world, that I had ever come across of deforestation by people.

NARRATOR: Throughout the island, excavations have revealed the impressions of countless palm root molds like these.

CARL LIPO: This island once had a palm forest, and one way we know that is because of the preservation of these palm roots that document that there once was a palm forest, a very extensive palm forest, across the island. These lines here, these black lines, trace the paths that the roots of the palm trees once made.

NARRATOR: But some scientists believe that the trees were cut down, not in a frenzy of statue building and moving, but for the simple reason that these were farmers.

PATRICK KIRCH (Archaeologist): These people were agriculturalists, they needed to clear land. So, in a sense, the forests were largely superfluous to them. It's garden land that's essential to them, not palm forest that they couldn't eat. The whole notion that it was the cutting down of these trees that led to a collapse, if you will, of Easter Island, is a bit off the mark, in my view.

NARRATOR: Archaeologist, Pat Kirch studies human impact on island ecology. He's done a comprehensive study of the Mangareva islands, about 1,600 miles away. After the Pitcairns, they are the nearest islands to Rapa Nui and striking in their similarity.

Both Mangareva and Easter Island were nearly deforested and both once had large colonies of seabirds whose guano fertilized the soil. But on both islands, people caught and ate nearly all the birds.

PATRICK KIRCH: When you eliminate those birds, you disrupt that nutrient flow, and we think, on both Easter Island and Mangareva, the elimination of large seabird populations was a key factor in the inability of the forest to regenerate.

NARRATOR: The people also slashed and burned down trees to make way for farmland, and combined with the loss of seabird fertilizer, put their forest in jeopardy.

And there may be another factor. During excavations here, at Anakena Beach, the site of the first settlement on Easter Island, Hunt and Lipo unearthed evidence identifying what they believe dealt a significant blow to the forest: rats, possibly brought as accidental hitchhikers by the original voyagers from Polynesia.

Hunt and Lipo believe these rats played a decisive role in the deforestation of the island.

TERRY HUNT: We didn't really see the full significance of that until we started to realize that rats, as an invasive species in fragile environments like this, would play a pretty significant role in stopping regeneration of new trees. They would eat the seeds of the native trees, in this case the palm trees, and the palms would not regenerate, as they had done naturally.

WILLIAM PITT (Wildlife Biologist): This is the same species that was on Easter Island. This rat is originally from Southeast Asia and has spread through most of the central and west Pacific.

NARRATOR: Will Pitt is a wildlife biologist at the U.S.D.A. Wildlife Research Center in Hilo, Hawaii.

WILLIAM PITT: This is a female Polynesian rat. In the wild, a lot of these rats only have about a year life expectancy, but a female, like this, could produce four litters a year.

NARRATOR: When introduced to areas with abundant resources and no natural predators, statistically, the first generation of rats could have exploded to a million in just three years. Even a fraction of that number would consume a huge amount of food. And it turns out that the food the rats ate was palm nuts, inside of which are the seeds that would spawn a new forest.

Throughout the island, remnants of palm nuts show gnaw marks from rat teeth, supporting that argument.

PATRICK KIRCH: The role that these little Polynesian rats may have played in the deforestation is a very interesting one and a little controversial. It's a disruptive force, ecologically, but I'm skeptical that it was the sole or major force. And the reason I say that is that rats were transported to every island in the Pacific, but not every island got deforested, so it had to be some combination of some other factors, along with rats, that led to the deforestation.

NARRATOR: The forest was likely wiped out by a perfect storm of human impact: slash and burn farming, decimation of the seabird population and the introduction of an exploding rat population on the island. But did the demand for logs to help move the statues also play a role? Or will Hunt and Lipo's experiment deliver on an alternative explanation?

At the experiment site in Hawaii, the volunteers are about to get their first lesson in moving a moai.

CARL LIPO: So what we want to do, first, is have you do a tug of war. We want to divide into two groups with roughly an even amount of strength.

NARRATOR: The teams are learning how to work together, by working against each other.

TERRY HUNT: Because cooperation is so important, we actually want you to be in a situation where it's really tough to win.

CARL LIPO: On three.

TERRY HUNT and CARL LIPO: One, two, three.

VOLUNTEERS: Pull, pull, pull, pull.

NARRATOR: Balancing the teams will be vital to balancing the moai in the actual experiment,…

TERRY HUNT: Okay, you guys are a little too good.

NARRATOR: …so no one team can overpower the other.

VOLUNTEERS: Pull, pull.

CARL LIPO: I think we're balanced now.

NARRATOR: The volunteers then graduate from tug of war to balancing a 10-foot-tall wooden pole.

CARL LIPO: Ready? North, south.

This is the maximum height we'd tie the rope on the statue, to give you an idea.

NARRATOR: What seems easy with a four-by-four post may not come so quickly with a 10-foot-tall, five-ton statue.

CARL LIPO: That's good coordination.

NARRATOR: Through a traditional Hawaiian blessing, everyone on site is reminded of the cultural importance of what they're about to do. A Rapa Nui ritual is also included, and everyone shares in the eating of a white chicken cooked in an earthen oven. The aroma released upon opening the oven is said to feed the gods.

CARL LIPO: I do worry about the base, that the base isn't sharp enough, the fact that it's got the roundedness.

NARRATOR: To maneuver the five-ton statue, a crane operator attaches rigging to Hotu Iti's neck.

TERRY HUNT: Oh, my god, look at those cables stretching.

CARL LIPO: Let's back up here.

TERRY HUNT: Wow.

NARRATOR: The rigging will also act as a safety measure to prevent the statue from tipping over.

TERRY HUNT: Well done!

CARL LIPO: There it is!

TERRY HUNT: So this is the real test. We're sort of wondering, what if he doesn't stand?

Is he resting on the ground?

CRANE OPERATOR: No, he'll fall over.

TERRY HUNT: Oh, my god.

CARL LIPO: It's got to stand.

CRANE OPERATOR: Want me to come off and see what it does?

CARL LIPO: Yes.

TERRY HUNT: Yeah. Yeah. We need to see that.

CARL LIPO: Worst case scenario.

It's got to stand. It's got to stand. That's the whole key. It leans forward, because that's the way it was made.

TERRY HUNT: Oh, my god.

CRANE OPERATOR: It's going to fall.

NARRATOR: The statue will not stand on its own. Hunt and Lipo struggle to figure out why.

CARL LIPO: Well, at the moment, you can see the way the strap is, the way that it's hanging, the center-of-mass line, here, goes straight down, is in front of the base itself.

What we need to do is get it back so that this strap is hanging from over here, to get it behind this point there. Right now, it's just going to fall over. It's in a leaning position.

TERRY HUNT and CARL LIPO: Okay. So what can you do?

CRANE OPERATOR: Our plan is to turn this truck around. He's got rubber bumpers on the very back.

TERRY HUNT: Okay, okay.

CRANE OPERATOR: Support it like that, so we can get the straps out.

TERRY HUNT and CARL LIPO: Okay good, good, good.

TERRY HUNT: My impression is that, if he doesn't stand by himself, that we probably have something wrong.

NARRATOR: The ancient Rapa Nui didn't have a crane; their statues had to stand on their own.

The rigging straps are adjusted, but Hotu Iti still does not stand.

TERRY HUNT: At this point, I have no idea what we could do to make this work.

NARRATOR: If Hunt and Lipo can't get Hotu Iti to stand, it will be hard to prove that their walking theory has legs.

CARL LIPO: The only thing you could do is take away material in front or add material on the bottom.

NARRATOR: Finally there's a solution.

TERRY HUNT: It needed that much.

It turns out it needs just a tiny bit of help. In fact, it's a two-by-four that's now resting right at the front of the base, and that tiny bit of addition, there, has balanced the moai. He's standing on his own. There's no pressure on the cables.

CARL LIPO: It may be that they were always made to be unstable when they're moving. They were carved in such a way to always be falling, and what you would do is you add something like what we did with the two-by-four, or maybe a stone—things we do find in the archaeological record—underneath the front to stabilize it.

NARRATOR: Along the moai roads on Easter Island are water-worn stones, like these, that may have been used this way.

CARL LIPO: Sergio Rapu actually mentioned this a number of times, kind of consistently finding these flat "poro" stones. And they're not just any old stone, they're very dense, and you find them on the roads over and over again.

TERRY HUNT: We're nervously learning a lot as we try to do this, and that's science. It's great to be wrong, and we realize that there are a few other things that need a little more emphasis in our understanding.

NARRATOR: Before it's time to make the first attempt at moving the replica, the volunteers sit down to watch the training video, to see how the statue should move.

CARL LIPO: As we talked about, the D shape is one of the keys. It's being leaned over to the side, and then it falls forward and rocks on that front edge.

I think we can do it. I think we have the force, we have the manpower, so now the question is getting the details.

NARRATOR: Before they try to move Hotu Iti, the volunteers need to make sure they can hold the statue upright.

CARL LIPO: I just want to see, and figure out, with everybody, if we tie it at the highest point, can we hold it back.

TERRY HUNT: Okay.

How many people do we want?

CARL LIPO: Ten, so five on each side.

TERRY HUNT: Okay, we need five on each side, so six more people.

CARL LIPO: Team leaders in the front, if it seems like you can't hold it, as he releases the pressure from the crane, yell out, so we can stop and he can add more pressure.

Yeah, let's move the wood.

TERRY HUNT: Oh, wow, okay.

Okay, so now he's going to release the tension, and it's going to be up to you guys to keep it from falling forward. It's going to want to fall forward. Yell out if it's too much.

Okay, coming down.

Can you feel it?

VOLUNTEERS: Yeah.

CARL LIPO: Is it a lot?

VOLUNTEERS: Moderate.

CRANE OPERATOR: I'm all off.

TERRY HUNT and CARL LIPO: All off!

TERRY HUNT: You guys are holding up the statue.

CARL LIPO: The question is going to be getting it full on its front edge, which I think we can do with just two teams. This was always our idea: that the teams that are pulling are actually behind the statue, keeping it from falling forward while rotating it at the same time.

NARRATOR: With the safety rigging attached to the statue, Hunt and Lipo finally have the chance to test their walking theory.

CARL LIPO: Starting out with Team A, I want you to pull a little harder, to see if we can rock it just a little bit.

VOLUNTEERS: Pull, pull, pull.

CARL LIPO: Okay, hold it.

I want you guys to spread out a little more, so that you're holding it, but more at an angle. Does it get harder? Or is it about the same?

VOLUNTEERS: Easier?

CARL LIPO: Easier at this angle? I want Team A to pull to see what happens.

VOLUNTEERS: Pull, pull, pull.

CARL LIPO: All right, hold. How's that? You guys exhausted?

NARRATOR: The teams continue to move farther and farther apart, simultaneously pulling and trying to twist the statue, but it's just not working.

CARL LIPO: We're going to want it lower, the ropes lower,…

TERRY HUNT: Yeah, yeah, okay.

CARL LIPO: …because we have no leverage up there.

TERRY HUNT: But it looks like it's not so hard to hold it back right now, so if it's around the neck, shoulder area, you can hold it back and probably tilt it.

CARL LIPO: So, we're going to have to try re-roping it.

NARRATOR: As they reach the end of the day, Hunt and Lipo have to face the reality that, so far, the experiment has failed. Unless they can get back on track, they won't know how the statues walked or what happened to the island's once robust and productive people.

No matter how this island was deforested, without any trees, wind and salt spray damaged the already poor soil. Seabirds were gone, as both a source of food and nutrients that had once increased the land's productivity. Some believe the loss of large trees meant they couldn't build canoes to leave the island. In one view, this is an environmental disaster leading to cultural collapse. But, building on previous research, Hunt and Lipo came to believe that the islanders found a new way to adapt to the crisis.

TERRY HUNT: When we were first surveying here on the island, we were really annoyed by the loose rocks that we would walk over. Then we looked a little closer, and we realized this was actually an area that was used for cultivation. And then, on top of that, we would see the taro growing in the rock areas and not in the soil areas. It was kind of backwards from what we might have expected.

NARRATOR: It confirmed what previous archaeologists believed: that what look like random piles of rubble are evidence of an ingenious method to improve the soil, called rock mulching.

TERRY HUNT: As you add the stones to the poor soil of Rapa Nui, you are increasing the nutrients available to plants.

NARRATOR: In addition to the phosphorous that leaches into the soil, the rocks help the soil retain moisture.

TERRY HUNT: If you look at rock mulch across the island, there are probably billions of stones that are moved. I mean it's just incredible how much rock has been moved and concentrated into efforts that had to do with cultivation.

NARRATOR: But was it enough to stave off disaster?

PATRICK KIRCH: We have to really admire what the Easter Islanders were doing, but not think that it was making their island into some incredibly productive system. It just helps to put off a worse kind of agricultural collapse.

NARRATOR: When Pat Kirch studied the islands of Mangareva, 1,600 miles away, he found the same kind of deforested landscape as on Easter Island, but, ultimately, the outcome for the people there was different.

PATRICK KIRCH: When you compare Easter Island and Mangareva, both were heavily deforested, but on Mangareva, there's a huge lagoon, barrier reef, very rich marine resources, so the Mangarevans turned to those marine resources and really depended on them to develop their economy. On Easter Island, there's essentially no reef, very limited coral, very limited fish.

NARRATOR: So, with their backs to the wall, did Easter Island descend into conflict?

SERGIO RAPU HAOA: The population was growing the scarcity of resources, and a lot of competition, social conflicts started building up and tensions between groups. Toward the end of Easter Island pre-history, there was a lot of war, a lot of conflict between one group and another.

NARRATOR: These sharp-edged obsidian implements, found scattered across the island, are often seen as the smoking gun: weapons, proof of a people at war.

SERGIO RAPU HAOA: What I have in my hand is an obsidian tool, and I think, definitely, it was used for defense or attack as a weapon.

NARRATOR: But again, Hunt and Lipo disagree, saying these obsidian implements were everyday tools.

TERRY HUNT: The edge here has a lot of use wear that's consistent with carving, with wood, hard materials, and use with plant materials.

NARRATOR: But these implements have actually been found embedded in human skulls.

SERGIO RAPU HAOA: I think most of the evidence we have, it points more to use as a weapon. We have found caches of them next to a skull that the mark exactly the shape of this tool is engraved on the skull.

NARRATOR: The remains of some 500 Rapa Nui people have been studied to get a clearer picture of just how violent this society was. Enough of these bones show signs of injury and trauma that experts believe this was a place of significant conflict.

PATRICK KIRCH: In my view, it was a society in distress. It had a lot of problems. They were pushing their agricultural system very hard. I think there's good signs that warfare was periodic and endemic.

NARRATOR: This tumultuous period began before European contact, which came in 1722, when a Dutch merchant ship arrived on Easter morning, hence the name of the island. As more Westerners arrived, stories about the island grew more lurid, even incorporating tales of cannibalism.

TERRY HUNT: Cannibalism seems to turn up when Europeans start to talk about it a lot, in the mid-19th century. We don't see any evidence like that on Easter Island. We don't see chopped up human bones, we don't find human remains in the earth ovens. There's good reason to believe that the 19th century idea of cannibalism is that you were not yet Christianized, so you're a Christian or you're a cannibal, and "cannibal" had, sort of, a generic meaning.

NARRATOR: So could it have been something other than violence that spelled the downfall of Easter Island society?

TERRY HUNT: We know, over and over again, when Europeans arrived in the Americas and in the Pacific, they introduced disease. They did so really unwittingly.

CARL LIPO: For example, I mean, a disease like cholera would have a devastating impact on this population,because it's water-borne, and once the disease gets in the water supply, it's going to be easily passed on to other people. And as they got sick it would pass on to them.

NARRATOR: In the 19th century, Peruvian slave traders also abducted hundreds of Rapa Nui people. By 1877, ravaged by slavery and disease, a devastated remnant of the people, who over centuries had carved and moved massive moai, had plummeted to only 110. But their oral history remains a tantalizing collection: tales of warfare, ritual, exploration and statue-building.

SERGIO RAPU HAOA: Whatever passage of oral history we have, we protect it like precious information. And, in our doing of archaeology, experience tells me how important it is to listen carefully to these little bits of information from oral history.

NARRATOR: The oral history says the statues walked, and Hunt and Lipo are trying to figure out whether it's true.

It's nine a.m. on the last day of the experiment: ...

CARL LIPO: Okay!

NARRATOR: …just eight hours left to figure out how to move a moai.

CARL LIPO: Let's be optimistic.

TERRY HUNT: Yeah.

CARL LIPO: How about there?

NARRATOR: Hunt and Lipo decide to set a goal, marking a finish line at 50 yards.

TERRY HUNT: We've got this marked at 50 yards, 25 yards and 10 yards. Be great if we got it even part of that way.

CARL LIPO: What we want to do is have the knot right here.

TERRY HUNT: Yeah. So it gives us the most pull.

NARRATOR: After spending the morning tying, re-tying and tying the ropes again, it's 11:30 before the experiment teams make their first attempt of the day to move Hotu Iti.

Until they master the motion to move the statue, the crane rigging will act as a safety.

CARL LIPO: We're going to start with the two ropes and the two large teams. We've got longer ropes this time, so we've got more room for you guys to pull.

You guys ready over there?

VOLUNTEERS: Yes!

CARL LIPO: We're going to let your side go forward, to let it lean forward, but you guys are going to pull at the same time.

TERRY HUNT: We're going to see if we can twist it slightly.

CARL LIPO: Ready, set, pull!

VOLUNTEER: Heave!

CARL LIPO: Let it go forward. Pull!

VOLUNTEER: Heave!

CARL LIPO: Okay, hold, hold.

NARRATOR: With no luck on the first attempt, the problem-solving begins.

CARL LIPO: Yeah, widen that out. That's good.

TERRY HUNT: Okay.

CARL LIPO: Go.

VOLUNTEERS: Heave ho, heave ho.

CARL LIPO: Okay, hold. Okay, you got it twisted! Now, we want to see if we can get the other way.

NARRATOR: No matter what they try or how they move, the team can't seem to twist the statue forward even an inch. Over the next hour, the statue doesn't budge.

CARL LIPO: Okay, hold.

TERRY HUNT: It seems to be swinging and rocking but not moving forward.

CARL LIPO: Things are exactly what we want. You have to trust in the way it moves, and if it fails, we have a crane.

TERRY HUNT: Trust the ancestors here!

CARL LIPO: Okay, so you're going to be pulling?

NARRATOR: They continue to try, but rocking Hotu Iti forward and back is the best they can do.

VOLUNTEERS: Heave ho, heave ho, heave.

NARRATOR: In fact, it's the only thing they can do, for hours.

Hunt and Lipo are convinced the ropes need to be around the shoulders to get the leverage needed to twist the statue at the base.

CARL LIPO: Can we get tension on the statue?

NARRATOR: They adjust the ropes again, even taking the advice of a nautical knot expert when nothing else is working.

(Rope Expert): As long as there's tension on here, that won't slip. I think they really want the purchase to come from right here, so it's on the shoulder.

CARL LIPO: Ready, set, go.

VOLUNTEERS: Pull, pull, pull.

NARRATOR: The clock keeps ticking; just three hours left to figure this out.

CARL LIPO: Whoa! We almost lost it there.

NARRATOR: Hunt and Lipo struggle to understand why two ropes aren't working to move the statue forward, since it worked with the wooden model. They decide to try something else, and everyone has an idea.

CRANE OPERATOR: It was a lot easier yesterday, when we were up high.

BEN: That's where I feel it's going to happen, don't you?

VOLUNTEER: Have a rope on the top, keeping it from falling, so there's three, like a Y.

VOLUNTEER: Pulling this rope right now, it's not going to work. We're fighting each other.

CARL LIPO: So one rope up there? Just holding it back?

VOLUNTEER: There'd be one rope holding him back.

VOLUNTEER: We have a third rope?

CARL LIPO: Yeah we do.

(Demonstrating on water bottle) Nothing's happening. Basically, you can move it like this or like this, but we can't really get it to do what it's supposed to do. So, what we've done is added a third rope, which, I think, we think is going to be really critical.

TERRY HUNT: Now, we think, with three teams, we're going to be able to get the motion going, take advantage of the kinetic energy that's built into the statue, allow it to fall forward on the front edge of the moai but the team in the middle not allowing it to fall too much.

NARRATOR: As they re-tie the ropes, Lipo and Hunt make a new observation. Thinking back to the fallen statues on Easter Island, they remember moai in transport had sideways V-shape notches where the eyes should be, a feature that now seems very important.

CARL LIPO: The V-shape of the eyes and the bridge of the nose is perfectly suited for tying a rope around and creating a place that you can put ropes and have friction. And it's also tall enough to provide the leverage you need to move it.

TERRY HUNT: Perhaps the finishing is done—because that area takes a little abuse, because of the ropes tied up high for that leverage—and so you finish them, add the eye sockets, when the statues reach their final place on the platforms.

NARRATOR: It's an intriguing find, but it's getting late in the day for discoveries.

CARL LIPO: So we're going to alternate pulling. You guys are going to be pulling back and then releasing.

NARRATOR: It's four p.m. There's just one hour left to figure out how to make this statue walk.

With the 10 people in back and more people on each side, they're ready to try one last time.

CARL LIPO: Release the tension.

How you guys doing? Good. Okay.

Ready, set,…

VOLUNTEERS: Heave ho, heave ho, heave ho, heave ho.

TERRY HUNT: Oh, my god.

CARL LIPO: Whoo!

TERRY HUNT: Yeah!

VOLUNTEERS: Heave ho, heave ho.

TERRY HUNT: He's walking!

VOLUNTEERS: Heave ho, heave ho.

CARL LIPO: All right, hold up. Awesome. Whoo!

TERRY HUNT: Okay, that was walking.

NARRATOR: As the statue starts to move a few feet, it all starts coming together, and the safety straps come off.

TERRY HUNT: The crane is up. We're taking…the training wheels are off. We are going to move the statue without any help.

Exhilarated and just amazed, really happy. And we're going to get right back to it.

CARL LIPO: Let's go for the finish line!

TERRY HUNT: So, this is how you move a moai.

VOLUNTEERS: Heave ho, heave ho.

NARRATOR: Once the teams get the hang of moving the statue, it becomes easy. Confident in their ability, they get a little overzealous….

EVERYONE: Oh, no!

NARRATOR: And Hotu Iti takes a nosedive.

But there's learning, even in failure. When Hotu Iti fell, he fell exactly the same way the ancient moai on Easter Island fell. Face first, at an angle, right along the road.

TERRY HUNT: In most cases, when the statues fell, they weren't able to retrieve them. We've seen a couple of examples on the roads.

CARL LIPO: I mean, some of the smaller ones they probably, undoubtedly, propped back up, but once they got larger and larger it became a pointless effort.

NARRATOR: Hotu Iti fares better, thanks to modern machinery.

With just minutes left in the day, Hunt and Lipo revise their goal of moving the statue 50 yards.

CARL LIPO: We're going to call this point, at 10 yards, the goal line, and once we get it there, that's going to be our finish, and we know we could move it anywhere, absolutely anywhere.

VOLUNTEERS: Heave ho, heave ho.

TERRY HUNT: I feel fantastic. This has been a great success. About, mid-afternoon I was feeling pretty low and I'm pretty high right now. It moved exactly the way we thought it would, we just had to figure out how to get it started. What struck everyone was that, once we got going, there was almost no effort involved. We were on the ropes, and we could feel that first tug was work, and then, when it started swinging, you could feel—I mean, we weren't even pulling on the ropes—that the energy of the statue moving did all the work. We were just kind of gently directing it.

CARL LIPO: The method, the inputs that we're doing a ten-foot version of are exactly the same that would be required in a 30-foot version. All that would matter was scaling the initial input of energy.

NARRATOR: In later experiments, Hunt and Lipo were able to move the statue more than 100 yards, in only 40 minutes. They also successfully walked Hotu Iti up grades of three to four percent.

We may never know if this is how the statues were actually moved, but this success presents an intriguing new explanation. It perhaps goes one step further to solving the mystery of what happened on Easter Island.

SERGIO RAPU HAOA: What we are doing today, we're pinpointing the archeological evidence that comes from oral history: the moai walk. The transportation of the statues is perhaps the most important contribution of this culture to humanity.

NARRATOR: If this really is how the islanders moved the statues, it raises an important question: do these statues that rise above this ravaged, treeless landscape serve as a cautionary tale for our times, or as monument to the human ability to innovate, create and survive?