I'm back on Rapa Nui - so I'm restarting this blog. Many people enjoyed the blog when we were on the island to begin the project, so perhaps you will enjoy a burst of new posts, and then sporadic posts describing what we found … and what we still don't know.
Mark Horrocks and I have arrived back to the island trying to settle a few loose ends. Our work to date has been fairly successful. Mark has taken the lead publishing many of our findings, highlighting his ability to identify microfossils showing which depths in our cores show fossil evidence of starch grains and photoliths, and therefore indicate arrival of polynesian crops. When combined with soil nitrogen studies (including nitrogen isotopes in the soil cores we sampled), the evidence in our lake and soil cores shows that polynesian agriculture was extensive. We have some questions to resolve about the timeline of agriculture, as we work toward publishing our findings.
I'd like to frame today's post by thinking about the long stream of researchers who have been attracted to the mysteries of Rapa Nui and Pacific migration. This area has a long and famous history. You'll remember that we focussed heavily on testing Jared Diamond's Collapse to design our project.Today, I'd like to focus on Thor Hyerdahl's Kon-Tiki. Hyerdahl is famous for sailing from Peru to Eastern Polynesia on balsawood raft, called Kon-Tiki and constructed using known South American techniques, to prove that it was possible for Polynesia to be settled from Peru. I've converged on Kon-Tiki as an example for two reasons. First, to help mark the march of time I found my Grandfather's 35 cent copy of Kon-Tiki (pictured) neatly on an old shelf of 1950's Reader's Digests. As I was finishing it on the way to Rapa Nui via Chile, I also noticed that movie called Kon-Tiki was also available on the plane - but it wasn't much good after reading the book. So Kon-Tiki is too much to pass up, and here's why.
Imagine being a researcher trying to understand Pacific migration at the time of Heyerdahl's adventure in 1947. Libby was just inventing radiocarbon dating. So scholarly evidence of the march of time relied on descriptive tools such as the passing of human generations in oral history, and the styles of artefacts such as pottery. With the help of radiocarbon dating and similar methods to precisely calibrate time in any location, Heyerdahl's fascinating idea of eastward migration has now clearly been overwritten by the archeological evidence of westward expansion. First, Western Polynesia was settled at the time of Lapita culture (3000 years ago), and then Eastern Polynesia (e.g., the Society Islands) and finally the far corners of the Polynesian Triangle - Hawaii, New Zealand and Rapa Nui. Recent work led by New Zealander Janet Wilmhurst has focused on compiling a large database and then using only the most reliable radiocarbon dates to identify the time of Polynesian settlements in Polynesia. She shows that all three corners of the Polynesian Triangle were settled right around 800 years ago. What a difference 60 years of research has made. The archaeology of Pacific migration is clear. However, some of the same mysteries that Heyerdahl sought to solve still remain. Evidence emerging from DNA and microfossils continue to provide tantalising evidence of east-west exchanges of people and agricultural organisms. Heyerdahl also argued that exchanges of art and culture accompanied the kumara (sweet potato) on an eastward course.
Certainly, Heyerdahl's thesis has been disproven if it is all or nothing. But the archeological understanding of westward migration leaves some mysteries, largely in the apparent dispersal of organisms between South America and Polynesia. As evidence of east-to-west exchange continues to emerge, perhaps we can solve some mysteries a step back and look somewhere between Kon-Tiki's script and today's headlines. The raft Kon-Tiki was able to steer eastward, but was clumsily unable to tack against the wind, even if someone fell overboard. In contrast, recent headlines remind us that the Polynesian double-hulled sailing waka technology has been revived, and now proven its ability to sail easily from New Zealand to the other corners of the Polynesian triangle. The remarkable reconstruction and demonstration of Polynesian sailing should remind us in 2013, much as Heyerdahl's voyage overturned the desks of academic naysayers in 1947, that Polynesian voyages of discovery and exploration were entirely feasible.
In other words, understanding Polynesian's true sailing ability may change our understanding of the evidence we're looking for, and our willingness as scientists to accept it. Brief visits won't leave much enduring archaeological evidence; and so far, there remains no verifiable scientific evidence of arrival and settlement in the corners of the Polynesian triangle substantially earlier than 1200 AD. But exploratory or trading waka visited a place, it is entirely sensible that they may leave organisms behind, and with observable fossil evidence through pollen, starch grains, or phytolyths. Do we see hints of this?
The goal of our project is to understand the dynamics and magnitude of "Collapse", if indeed a collapse occurred. To do so, we need to put evidence on a timescale and need to think about how to scientifically evaluate and further test evidence that could show the early arrival of organisms but not necessarily imply settlement. And so we are here again, thinking hard. As we attempt to draw our project to a close, it is very interesting to think about how much understanding can change over 60 years, as it has since Kon-Tiki was published in 1950.
After G W Bush's "mission accomplished" event on the deck of the aircraft carrier involved in the Iraq invasion, I'll never utter these words without a question mark after them. With the question mark added, they are apt for our last day here. We think we've got a great set of samples to bring home. The map I'm including shows they're well distributed across the island. But until we do the work in the lab, we won't really know if we've accomplished the mission.
Dave's idea of packing for a big overseas field trip is to find old shoes that are about die, and to wear them until they die. This seems risky to me, but at least means he doesn't have to clean them to get back into NZ.
Today was our last full day on the island, so Dave went for a long hike. When he returned, he pronounced his shoes to be dead.
Today was our "day off" again, which meant we started packing and writing our report.
I thought I'd tell you about the mana vai which the people of Rapa Nui used, and still use, to grow crops. Within stone walls, the plants are well protected from the wind; this conserves water (vai). This is very helpful for the more tropical plants brought from Polynesia. Here our guide Soro has ginger in one hand and a sugar cane in the other. Mark and John were impressed, and there's more sugar cane behind John.
The other photo shows a much tidier mana vai, which we saw in the same area while we were looking for places to sample soil.
Today we sampled a site quite some distance around the north coast. Here's a view of our site (with a calf for scale), which contained about 2 meters of nearly rockless soiI. It took researchers a long time to recognize that all these rocks were put in place by people to reduce water losses from cultivated plants. Amazing, eh?
Today we're continuing with more soil coring. I'll post some photos of this tomorrow.
I thought I'd post today about improvisation. Working in a remote place often involves some improvisation. There have been many ways we've improvised on this trip, and here's one. Normally, we like to dry samples in nice ovens, or better yet in freeze dryers. For samples that had to be dried here, I "built" this cute little oven. It consists of a box with a hole cut in the bottom to go over a light. With the help of a tripod and an extra bed, the box was stable for an
overnight drying session. And as you can see from the lower reading, it hit my target range of 35-40°C nearly perfectly.
Warning: be careful with heat. I checked the temperature around the light bulb quite a few times to be sure I wasn't a fire hazard. John reports that an older tactic was to use a candle as a heat source, and he caught his plant samples on fire once!
As our soil sampling has proceeded, we've been able to refine our visual target for sites. We're trying to find sites that naturally collect sediment from a significant uphill area with both human occupation and agriculture. As we've proceeded, our skill has improved at finding sites that collect sediment efficiently without being scoured out during major floods. This site was nearly ideal. It samples a large area upstream of gorge in the background.
The exact location we sampled showed evidence of almost continuous soil burial, but had to be chosen carefully because areas directly downstream of the gorge appeared to be scoured out during floods.In the sample shown, the core is composed entirely of material dark enough to be a topsoil, but the sample is from 1.2 - 1.5 m below the soil surface. Throughout most of the island, soils at this depth would be light reddish brown.
Studies of lake sediments and climate at Rano Raraku -- the crater where nearly all the moai (statues) have been carved -- have suggested that lake level was once higher (at the end of the last glacial period). In the process of identifying soils to sample, we've stumbled onto what seems to be previously overlooked evidence for a high stand of lake level. In addition to large areas of "ironpan" development consistent with a vegetated peaty lakeshore, we found large numbers of fossil roots which we can use to partially identify the plants that once occupied the lakeshore.
With the benefits of good access and additional help, we were pleased to finish off our coring here in only two days. Here you can see our coring raft on the lake.One of the most remarkable aspects of the crater (after the moai of course) is the rapidly eroding red soils. The red soils are diagnostic of volcanic terrains in the tropic and subtropics. The erosion here is interesting, because it is relatively rare to see such pronounced erosion on the island -- despite the reputation Easter Island has for erosion, I remain unconvinced the problem is as serious as in many other parts of the world. In Rano Raraku however, I'm amazed by he energetic herds of wild horses with dust flying behind them. They must be both drawn and energized by the water source. As Mark puts it, they are "just horsing around."