Explain how scientists know that rock layers at the bottom of the Grand Canyon are older than those found on the rim.

The Principle of Superposition is like the main idea behind understanding rock layers. Think of rock layers as being like a stack of papers. The ones at the bottom got there first, so they're the oldest. In geology, this means the oldest rocks are found at the lowest levels, while the newer and younger rocks pile up on top of them over time.
When studying rock layers, scientists look at how these layers are stacked on each other. Especially in places like the Grand Canyon, where you can see many exposed layers, the deepest layers are from a much older geological time period compared to the top layers.

Radiometric dating is a cool scientific method that helps us figure out how old something is by looking at radioactive elements. These elements break down over time at a known rate, like a really slow clock.
Here's how it works: Rocks contain tiny amounts of radioactive elements. Over millions of years, these elements change into something else. By measuring how much of the original radioactive material is left compared to the new material, scientists can calculate how old the rock is.
This method is very reliable and has been used to confirm the age of rock layers at the Grand Canyon. Radiometric dating proved that the rock layers at the bottom of the canyon are much older than those at the top. This matches up perfectly with the Principle of Superposition.

Fossils are like nature’s history books. They tell us about the plants and animals that lived millions of years ago. Fossils can also help scientists figure out how old rock layers are.
When a fossil is found in a particular rock layer, it can be compared to other similar fossils that have already been dated. If scientists find a fossil in a lower rock layer, they know that layer is older than one with a later fossil. This method relies on the fact that certain types of plants and animals only existed during specific time periods.
In the Grand Canyon, fossils help confirm that the oldest layers are at the bottom. By finding and dating these fossils, scientists add another piece of evidence to the puzzle of determining the age of rock layers.

Geological features are like clues that help scientists decode Earth's history. These include things like faults, folds, and intrusions.
A fault is a crack in the Earth’s crust where rocks have slipped past each other. An intrusion is when molten rock cuts through existing layers and cools to form new rock. These features can be used to tell the relative age of the rocks they affect.
According to the Principle of Cross-Cutting Relationships, if a fault or intrusion cuts through a rock layer, the rock layer must be older than the fault or intrusion. For example, if a fault cuts through several layers of the Grand Canyon, we know the layers had to be there first, so they are older than the fault.
By studying these features, geologists get a clearer picture of how different layers and events occurred in Earth’s history. This helps confirm that the deepest rock layers in the Grand Canyon are the oldest.