As we learned in the previous lesson, index fossils and superposition are effective methods of determining the relative age of objects.
In other words, you can use superposition to tell you that one rock layer is older than another.
Another example of yearly layers is the deposition of sediments in lakes, especially the lakes that are located at the end of glaciers.
Rapid melting of the glacier in the summer results in a thick, sandy deposit of sediment.
To accomplish this, scientists use a variety of evidence, from tree rings to the amounts of radioactive materials in a rock.
Radioactive materials in Earth's interior provide a steady source of heat.
Calculations of Earth's age using radioactive decay showed that Earth is actually much older than Thomson calculated.
Using logs recovered from old buildings and ancient ruins, scientists have been able to compare tree rings to create a continuous record of tree rings over the past 2,000 years.
This tree ring record has proven extremely useful in creating a record of climate change, and in finding the age of ancient structures. The thick, light-colored part of each ring represents rapid spring and summer growth.
Scientists analyze these ice cores to determine how the climate has changed over time, as well as to measure concentrations of atmospheric gases.