Unit 6 Lesson 1 Relative Dating vs RadioActive Dating of Fossils

The Law of Superposition

What It Means: In layers of rock, the oldest rocks are at the bottom, and the younger rocks are on top.

Easy Example: Think of a brick wall where you build the bottom part first.

Paleozoic Rock Layers

Question: Which Paleozoic layer is the oldest? D) 7

Geologic Cross Section

Question: Identify the youngest rock layer. D) Layer with dinosaurs

Unconformities in Geology

Law of Crosscutting

What It Means: If something cuts through another rock layer, it is younger.Example: An igneous dike cutting through sedimentary rock.

Law of Inclusions

What It Means: A rock piece inside another rock is older than the rock it’s in.Concept: Weathering can break down older rocks into sediments.

Understanding Rock Layers

Clothing Example: The way clothes are stacked in a laundry basket can show the order of rock layers.

Superposition: It means 'over' or 'above' in Latin, which helps us understand how rock layers are placed.

Index Fossils

What They Are: Fossils from species that were around for a short time but were found in lots of places.

Characteristics: They are unique, found in many places, and lived briefly, like trilobites in Paleozoic rock.

Fossil Evidence

Support for Grand Canyon

Ocean Claim: Fossils of ocean animals in rock layers show that the Grand Canyon used to be covered by an ocean.How Fossils Help with Dating: Comparing fossils helps us figure out how old rocks are.

Dating Methods

Relative Dating

What It Means: Rocks lower in layers are older, but this method does not give exact ages.Use: We can use layers of fossils to help date the rocks.

Radioactive Dating

What It Is: This method measures how long it takes for radioactive elements in rocks to decay to find their ages.Half-Life: This is how long it takes for half of a radioactive substance to break down.Elements Used: Carbon-14 is for dating newer fossils; Potassium-40 is for dating really old ones.

Summary

The Law of Superposition shows that the oldest rocks are below the younger ones. We use laws like Crosscutting and Inclusions to find out more about rock layers. Index fossils are helpful for dating rocks and show places that were once oceans. Relative dating gives us a guess, while radioactive dating gives more precise ages based on element decay.