What Happened to the Sun over 7,000 Years Ago? "Highly Abnormal"

By analyzing the level of a carbon isotope in tree rings from a specimen of an ancient bristlecone pine, a team led by Nagoya University researchers has revealed that the sun exhibited a unique pattern of activity in 5480 BC.

An international team led by researchers at Nagoya University, along with US and Swiss colleagues, has identified a new type of solar event and dated it to the year 5480 BC; they did this by measuring carbon-14 levels in tree rings, which reflect the effects of cosmic radiation on the atmosphere at the time. They have also proposed causes of this event, thereby extending knowledge of how the sun behaves.

When the activity of the sun changes, it has direct effects on the earth. For example, when the sun is relatively inactive, the amount of a type of carbon called carbon-14 increases in the earth’s atmosphere. Because carbon in the air is absorbed by trees, carbon-14 levels in tree rings actually reflect solar activity and unusual solar events in the past.  The team took advantage of such a phenomenon by analyzing a specimen from a bristlecone pine tree, a species that can live for thousands of years, to look back deep into the history of the sun.

Picture of the bristlecone pine forest in California, the United States where the bristlecone pine sample for this study used to live. In this forest, there are many living old trees exceed 1000 years old. Harsh environments make bristlecone pines very dense and long lives.

Contacts and sources:
Koomi Sung

Nagoya University

Citation: “Large 14C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene” was published in PNAS at: www.pnas.org/cgi/doi/10.1073/pnas.1613144114