Layers that form in ice are similar to tree rings because both create a year‑by‑year record of past environmental conditions that scientists can read like a timeline. Each new layer or ring represents roughly one year, and their thickness and composition show what that year was like.

Annual layers

In places like Greenland and Antarctica, snow that falls each year piles up, gets buried, and eventually compresses into distinct layers of glacier ice, much like pages in a book. Tree rings form as a tree adds a new layer of wood each growing season, creating a visible circle for each year when the trunk is cut across.

Environmental record

The thickness, color, and chemistry of ice layers (such as how much dust or trapped gas they contain) reflect conditions like temperature, snowfall, and volcanic eruptions during the year they formed. Similarly, the width and density of tree rings reflect how favorable that year’s growing conditions were, such as how warm and wet it was or whether the tree was stressed by drought or disease.

Reading time and climate

Scientists can count ice layers downward from the surface, just as they count tree rings outward from the center, to determine age. By analyzing many layers or rings in sequence, researchers reconstruct long climate histories, seeing patterns such as warm and cold periods, major eruptions, or long droughts recorded in both ice and wood.