Gold in Them Thar Rings

Tree trunks grow outward by adding new wood as rings. If you cut a slice from a tree trunk, you will see that it has rings, and by counting those rings you can determine how old the tree is.

Now, scientists using a nuclear reactor have detected gold in tree rings. They believe the gold is linked to volcanic eruptions.

"Initially, when we began this work at Cornell University, we were simply looking to see what elements in tree rings could be measured using neutron activation analysis," says Kenan Unlu, now at Pennsylvania State University.

They found gold in high levels in some rings, and recognized that these rings were added in years of known volcanic eruptions, including an eruption of Mount St. Helens.

So how does gold get into a tree? When a volcano erupts, trees have a more difficult time getting light because of all the ashes in the sky. Scientists believe that to make up for this, the trees try to pull more nutrients from the ground. Copper is one of the nutrients essential to tree growth, and gold is similar in structure so it probably gets pulled up by accident.

They are currently looking at the last 600 years to hone their skill with this procedure, and plan to look at trees from the last 6,000 years - which is as far back in time as the Cornell University tree library goes.

--Bjorn Carey

Credit: Greg Grieco, Pennsylvania State University