By Byron Perry
Easter Island is the most remote habitable strip of land in the world. The Juan Fernandez Islands is the nearest land, 1850 kilometres (1150 miles) to the east, while the nearest land to the west (the direction Polynesian colonists traveled from) is Pitcairn Island, 1921 kilometres (1200 miles) away. Despite these huge distances, Polynesian colonists settled the island around 1,200 AD, arriving with wooden canoes and stone tools with which they managed to build a complex and thriving civilisation. Over 1000 huge moai statues were carved and placed around the coast of the island. This required up to 86 tonne statues to be transported a maximum distance 18 kilometres (11 miles) from the Rano Raraku quarry where all the statues were carved. This was achieved purely with human muscle power, as the Rapa Nui had not discovered the wheel and had no domesticated animals except for chickens. However, by the time the Dutch arrived in 1722 the population had fallen from a peak of approximately 15,000 to 3,000. The moai had been toppled and the Rapa Nui had resorted to cannibalism. What happened? How could the civilisation fall without any contact with the world beyond the island?
Before the collapse
A row of moai statues at Ahu Tongariki. The red block of stone on the moai second to the right is called a pukao and represents a Rapa Nui topknot. (Easter Island Travel)
Easter Island is a roughly triangular island. Made up of three volcanoes, the island has an area of 163 square kilometres (63 square miles). Nowadays the island is entirely deforested, and there is not a single native tree left on it . The only native vertebrates living on the island are two species of lizard, making Easter Island one of the most ecologically damaged places on the planet. However, investigations have proved that there was a thriving ecosystem on the island, before the humans arrived. Pollen collects at the bottom of lakes and ponds. By taking samples of sediments at the bottom of pools on the island and examining the pollen in these sediments scientists can determine what plants grew on the island and how abundant they were. The age of these sediments can be calculated by radiocarbon dating.
Radiocarbon dating works on the principle that some of the carbon in our atmosphere, instead of the usual carbon-12 is a heavier, radioactive, isotope called carbon-14. Carbon- 14 is produced in the upper atmosphere in a reaction between cosmic rays and nitrogen. When carbon is ‘fixed’ in photosynthesis, carbon-14 is incorporated into the plant tissue. Animals then eat plants incorporating carbon-14 as well as carbon-12 in their bodies. When a plant or animal dies it stops acquiring more carbon. As carbon-12 is stable, the level of this isotope is fixed, but as carbon-14 is radioactive its levels slowly decrease as it radioactively decays. A recently dead plant or animal will have the same proportion of carbon-14 atoms as the atmosphere, while a dead plant or animal with half the proportion of carbon-14 will be roughly 5700 years old, the half life of carbon-14. By using this method and by sampling pollen found on the island scientists have discovered the island was once home to 21 tree species. Nuts were also found in a cave that belonged to a giant palm tree species. By comparing the size of the nut and the size of casts of the tree’s roots from volcanic eruptions to a closely related species in Chile (called the Chilean Wine Palm) scientists estimate that the tree had a trunk 2 metres (7 feet) in diameter and would have been even taller than the Chilean species. Which is 20 metres (65 feet) tall. This would have made the tree the largest palm tree in the world.
Scientists have also found the remains of possibly the world's largest seabird colonies in the world, with at least 25 species of seabird breeding on Easter Island. In present times no seabird breed on the main island. Six species of landbirds also lived on the island. All are extinct today. All of this evidence points to a complete destruction of the Easter Island ecosystem after the arrival of humans to the island.
How the collapse happened
As the Rapa Nui did not possess writing, it is difficult to tell exactly when they arrived on Easter Island, with estimates ranging from 300- 1200 AD. However, the current best estimate, from radiocarbon dating of charcoal caused by burning firewood, is that the Rapa Nui arrived at around 1200 AD. When the Rapa Nui arrived on the island, it was probably very conducive to their way of life. The huge numbers of birds were easy food, and the large trees enabled the Rapa Nui to build their large seaworthy canoes to go on fishing expeditions. The Island also had great stone for making the stone tools the Rapa Nui relied on. As the soil contains minerals such as potassium and phosphorus released in volcanic eruptions, the soil has good growing conditions for plants due to these minerals aiding plant growth. These upsides are balanced against the fact that Easter Island is quite dry, windy and subtropical, roughly as far south of the equator as Miami or Delhi is north. The Polynesians came to Easter Island with tropical crops such as sweet potatoes, sugarcane and bananas. Some of these such as coconuts did not grow on Easter. The Island is likely to have supported a population of 6000- 30,000 people, although the higher estimates are more likely. From 1200- 1600 the Rapa Nui developed a thriving civilization. Bigger and bigger moai were carved as chieftains competed against each other. The moai were not the only accomplishment of the Rapa Nui though. In order to better grow their crops huge amounts of stone were shifted to build windbreaks for their crops. Huge houses were built for the elites of Easter Island called hare paenga, shaped like canoes and up to 95 metres (310 feet) long. The Rapa Nui also built giant platforms to place the moai on, these could weigh up to 8200 tonnes (9000 tons). The sheer effort of moving this much stone by hand is truly incredible. For comparison a large van can typically carry up to 1.5 tonnes of cargo. This means that it would take almost 5500 trips in a van to move the same amount of stone that the Rapa Nui moved by hand without any labour saving inventions like the wheelbarrow. All of this points to the fact that the Rapa Nui were a highly successful civilisation. In total isolation they could devote enough people to carve and transport the moai, build the hare paenga and move the huge amount of stone to build the ahu, all with a population of a single modern town. So where did it go wrong?
The main root of the Easter Island collapse was the overexploitation of the natural resources of the island. Pollen trapped in sediments shows that between 1300 and 1600 the levels of tree pollen dropped dramatically, and almost entirely disappeared by 1600. The Rapa Nui cleared land for farming, but also to build canoes. It is unclear how the Rapa Nui transported the moai, but if they used wooden rollers this could have been another cause of deforestation (the other main theory is that they were ‘walked’ using two teams rocking the moai from side to side). At the same time, the Rapa Nui were unsustainably hunting the bird population of the island. By the time Captain Cook arrived in 1744 the seabird colonies had been eliminated on the main island and all the species of landbird were extinct. Nevertheless this calamitous destruction of the island’s ecosystem was not entirely due to shortsightedness. As Easter is a dry island in a subtropical climate, trees do not grow very fast, meaning that only a very low level of tree felling would have been sustainable. The Rapa Nui also introduced rats to the island. Whether the original colonists deliberately carried rats with them (as food, food taboos are not universal) or whether they were stowaways is unclear. Much like cane toads or rabbits in Australia invasive species have massive, mostly unpredictable results. The rats ate the nuts of the giant palm trees growing on Easter, stopping new palm trees growing to replace the trees being felled by the Rapa Nui. Virtually all of the palm nuts found in the island after the introduction of rats have rat bite marks on them, this would have stopped the nuts from germinating. The rats also ate the eggs of the birds on the island, having a massive impact on their population. The impacts of these combined factors on the local ecosystem was disastrous. The extinction of the birds removed a major part of the Rapa Nui diet. The complete deforestation also removed the nuts and fruit that grew in the forest, but also meant that the Rapa Nui had no way of constructing their large wooden canoes. This meant the Rapa Nui could not go on fishing expeditions, and were confined very close to the shore of their island as only very small canoes could be built. Virtually the only protein left in the Rapa Nui diet after the ecological collapse was chicken. Depending on how the moai were transported, it could have brought an end to the construction of the moai. Tree’s roots hold the soil together and slow down water flow. By removing the trees, soil simply was washed away, reducing the productivity of the Rapa Nui farms. The end result of the ecological collapse was societal collapse. The population of Easter Island fell 70% from its peak to when Europeans arrived. The moai were toppled in the 1700’s. Warlords gained power and a period of war ensued. An abundance of obsidian spear points from the 1600’s is testimony to this violent period. Contact with the outside world was as disastrous and tragic for the Rapa Nui as it was for most indigenous cultures. After contact with Europeans in 1722 and 1744 the Rapa Nui were tragically cut down by smallpox against which the Rapa Nui had no resistance. Peruvian slavers also took their heinous toll. Between 1862 and 1863 half of the island's population were abducted, and the island was annexed by Chile in 1888.
The tale of the Rapa Nui is a cautionary one. The Rapa Nui had developed a thriving and culturally rich civilisation. The chieftains rarely fought, instead competing through building taller and more elaborate moai. Indeed, the Rapa Nui reached their peak relatively close to the collapse. The tallest moai, Paro, was one of the last moai carved. However, their civilisation was struck down by unsustainable use of natural resources relatively soon after their cultural peak. Modern civilisation should take care not to succumb to the same fate as the Rapa Nui. Lest our skyscrapers become like the toppled moai.
Sources
Bloch, H. (2012, July 1). If Only They Could Talk. National Geographic, 31-49.
Diamond, J. (2005). Collapse: How Societies Choose To Fail Or Survive (2nd ed.). Penguin.