How do we date archaeological sites? Why a lake in Fukui Prefecture became the world's 'measuring stick'

IntCal: The Day Lake Suigetsu Became the World Standard

The Problem with Radiocarbon Dating

"Radiocarbon dating" (C14 dating), used in archaeology and geology, estimates age using the decay of carbon-14 in organic materials. Developed in 1949, it revolutionized archaeology.

However, this method had a significant problem. Atmospheric carbon-14 concentration isn't constant - it varies over time. Therefore, converting measured "radiocarbon age" to "actual calendar age" requires a "calibration curve."

Tree Ring and Varve Calibration

Traditionally, tree rings were used to create calibration curves. Since tree rings form one per year, their exact ages are known. Measuring carbon-14 in tree rings reconstructs carbon-14 concentrations for each period.

However, tree ring data had limitations. Available tree rings only extended back to approximately 12,450 years ago. Earlier dates relied on estimates with large uncertainties.

This is where Lake Suigetsu's varves came in.

Lake Suigetsu's Challenge

In 2006, Professor Takeshi Nakagawa (then at Newcastle University, now Ritsumeikan University) and his international research team began a project to perform radiocarbon dating using leaf fossils collected from Lake Suigetsu varves.

This project was distinguished by its thorough verification system:

- Samples collected: Over 800
- Each sample sent to 2-3 different laboratories
- Blind tests (measurements without knowing sample age)
- Rigorous cross-checking of results

This thorough verification gave Lake Suigetsu data unprecedented reliability.

Adoption into IntCal13

In 2012, Lake Suigetsu's radiocarbon data was officially adopted into the international calibration curve "IntCal13." This dramatically improved dating precision for approximately 10,000-50,000 years ago.

Professor Nakagawa stated: "It's the world standard for measuring history. Lake Suigetsu is the Greenwich Observatory of geology."

Just as Greenwich Observatory is the reference point for longitude 0 degrees worldwide, Lake Suigetsu became the reference point for world dating.

Contribution to IntCal20

In 2020, the further updated "IntCal20" was released. Lake Suigetsu data continues to play a crucial role.

IntCal20 enables calibration up to 55,000 years ago, applicable to Paleolithic site dating.

A Victory for Japanese Science

Lake Suigetsu's adoption into IntCal was also a major victory for Japanese science.

Previously, radiocarbon dating calibration curves relied on European and North American data. Lake Suigetsu data became the first major calibration data from Asia, elevating the international reputation of Japanese geology and archaeology research.

At the Fukui Prefectural Varve Museum, you can see actual samples of these historic varves. The records from this Japanese lake that became the world's time-measuring "yardstick" quietly await visitors.

[!] Various theories exist. Information may contain errors.