Geologists have some cool ways to figure out how old rock layers are. This is really important for understanding the history of our planet. Here are three key methods they use:

1. Radiometric Dating: This method looks at how radioactive materials break down over time. For example, carbon-14 is used for dating things that were once alive, like fossils. It has a half-life of about 5,730 years. This means it’s great for dating fossils that are up to 50,000 years old!

2. Stratigraphy: Geologists study the order of rock layers, called strata. They follow a simple rule: older layers are always below younger layers. This helps them figure out the order in which different layers were formed.

3. Index Fossils: Some fossils are helpful because they were found all over the world, but only for a short time. Geologists can use these special fossils to match the ages of rock layers from different places.

By using these methods, geologists can put together a clear picture of the Earth’s history and important events that have happened over time.