Most everyone was told growing up about how when a tree is cut down, you can look at the tree rings to figure out the tree’s age, and also how much the tree grew each year. Dendrochronology deals with this type of science, which can help us understand environmental conditions in the past – and even tell us whether a Viking ship was built in the year 819 or 820. Dr. Kevin Helmle, who is a research scientist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science (RSMAS) and NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), talked to students participating in the Digital WAVE program about another way to “tell time.” He works in sclerochronology, which means using layers in coral cores, in a similar way as rings in tree trunks. Annual layers of coral growth can be studied to provide information on environmental and climate history over many past centuries. Dr. Helmle brought real coral cores to show, and also showed students x-ray images of interior coral layers (see image below). By looking at the size and density of the layers, scientists like Dr. Helmle can determine things like the water temperature, water chemistry, and exposure to light the coral experienced at that time. Students then looked at the coral x-ray images, identified layers that corresponded to important years in their lives (or in history), and looked at real data for that year to find out what was going on in the oceans at that time. Just like real sclerochronologists!