# Tree Rings, Ice Cores, and Varves

##### Study Tip
All of these methods used to date events involve analyzing patterns on an object. Tree rings, ice cores, and varves keep track of time the same way a prison inmate may write tally marks on the wall. By looking at the patterns, a person is able to estimate a time frame of an event’s occurrence.

## Tree Rings

• Tree trunks display alternating bands of light-colored, low-density summer growth and dark, high-density winter growth
• The width of these rings varies with the conditions present that year, and shows the general temperature and humidity of the time.
• All the trees in an area during a given time period show the same patterns in their tree rings.
##### Study Tip
All of these methods used to date events involve analyzing patterns on an object. Tree rings, ice cores, and varves keep track of time the same way a prison inmate may write tally marks on the wall. By looking at the patterns, a person is able to estimate a time frame of an event’s occurrence.

## Ice Cores

• The alternation between snowfall in the winter and dust accumulation in the summer leads to a snow-dust pattern that appears within the ice.
• In order to see the patterns within the ice, scientists drill deep into the ice sheets, producing ice cores hundreds of meters long.
• Analysis of the ice tells how concentrations of atmospheric gases changed overtime, which can yield clues about the climate.
By counting the number of rings that a tree has, it is possible to find out how many years the tree had lived.
An ice core section shows annual layers

## Varves

• Varves are alternating layers of sediment, with thick deposits of sediment during the summer and thin, clay rich layers during the winter.
• Scientists analyze varves to learn clues about past climate conditions.
• A warmer summer may yield a very thick sediment layer, whereas a cooler summer may yield a thinner layer.
Ancient varve sediments in a rock outcrop
##### Concept Check
• How do seasonal differences change what we see in tree rings, ice cores, and varves? Describe in detail how each is formed.