We have all learned the important environmental role trees play in science classes: through photosynthesis, trees emit oxygen into the air and remove carbon dioxide.

But can trees also help us learn about history -- not just on Earth, but even in outer space! 

What are tree rings?

Trees have something unique that allows us to go back in time: tree rings.

Every year, a tree grows a new tree ring, so counting the number of rings tells us how old the tree is. However, the tree rings are much more useful to environmentalists than simply calculating age.

The tree rings grow differently depending on the environmental conditions of the year. For example, tree rings are wider in years of heavy rainfall and narrower in years of light rainfall.

A New Finding

Earlier this year, scientists discovered that certain trees in Japan had recorded the presence of two radioactive elements in the tree rings. Radioactive elements are a common tool used by scientists to determine an items’ age.

For example, if a rock were to be partially made of carbon-14, scientists could use the amount of carbon-14 remaining in the rock combined with the half-life of carbon-14 (around 5,730 years) to determine the age of the rock. Half-life is the amount of time it takes for half of the substance to decay.

But what makes this case different is that the elements carbon-14 and beryllium-10 -- formed by the decay of nitrogen atoms, were only found in a single tree ring. Considering that a new tree ring is added each year, this means that the two elements were in the environment for only one year.

Using the tree rings, the scientists also found that the high levels of carbon-14 and beryllium-10 had occurred around 774 A.D -- a time in history when no major events had been recorded. These observations led the scientists to wonder what caused such a dramatic—but a short-term influx of the two elements?

The Popular Theory

Researchers at the University of Jena in Germany believe that the spike in carbon-14 and beryllium-10 was caused by gamma-ray radiation. This type of radiation is caused when two dense objects, such as black holes, collide with each other in space.

This hypothesis supports the findings in the tree rings because a gamma-ray burst would cause increased levels of carbon-14 and beryllium-10. In addition, the collision—which would have occurred around 12,000 light-years away—would not be visible to people on Earth. Therefore, there would be no record of the collision.

While this suggestion seems to fit the observations, for now, scientists cannot say for certain what led to the elements in the tree rings.