Easter Island, famous for its imposing moai statues, is often presented as a case of sudden societal collapse. However, a recent scientific analysis offers a renewed vision of its history, based on climate data that has been little studied until now.
To achieve this, researchers from the Lamont-Doherty Earth Observatory traced the evolution of rainfall on this isolated island. Their study was based on analyzing sediment cores taken from local wetlands, such as Lake Rano Kao.
The method used by the team consisted of measuring the isotopic ratios of hydrogen preserved in ancient leaf waxes. This approach provides a direct record of rainfall variations, with continuity over nearly eight hundred years.
The results reveal a significant decrease in precipitation around 1550, which lasted for more than a century. Consequently, this period of drought permanently affected freshwater resources, which are essential for life on the island.
Contrary to theories of a sudden decline, the Rapanui communities demonstrated a notable capacity for adaptation. Thus, cultural changes, such as the reduction in the construction of ahu (ceremonial sites in the form of a platform usually topped with moai statues), coincided with this difficult climatic phase.
This discovery therefore challenges the popular narrative of ecocide, which attributed the decline to overexploitation of resources. Indeed, the climate data shows that environmental factors had a notable influence on social evolution.
Lake Rano Kao, a key site for sediment study.
Credit: William D'Andrea
The next steps in this research aim to explore sediment archives over longer timescales. This will allow for a better understanding of atmospheric dynamics in the southeastern Pacific, a region that is still poorly documented.
Understanding the Past Through Plant Chemistry
Isotopes are forms of the same element that differ in mass. For hydrogen, the ratio between heavy and light isotopes in rainwater changes according to weather conditions, such as evaporation or precipitation.
When plants absorb this water, they incorporate these isotopes into the waxes of their leaves. After they decompose, these waxes are preserved in sediments, effectively creating a chemical archive of past conditions.
By analyzing these ratios, scientists can estimate past rainfall levels with precision. This approach is particularly reliable for regions where historical data is limited.