Please get out your notebook!! Draw a chemical equation and label both sides in your Daily Question section

Relative and Absolute Ages The relative age of a rock is its age compared to the ages of other rocks. Example: Comparing your age with someone else’s age. When you say that you are older than your brother but younger than your sister, you are using relative age. What is relative age?

Relative and Absolute Ages The Absolute age is the number of years since the rock formed. What is absolute age?

Paleontology The study of fossils

The Position of Rock Layer How do scientist determine the age of sedimentary rocks? Geologist use the Law of Superposition to determine the relative ages of sedimentary rocks.

The Law or Superposition According to the Law of Superposition, in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it. What is the law of Superposition?

The Law or Superposition The walls of the Grand Canyon in Arizona illustrate the law of superposition. younger

Other clues to Relative Age Geologists use clues from extrusions and intrusions for igneous rock and faults. How else can you find the age of rocks and fossils?

Other clues to Relative Age Clues from igneous rocks: Extrusions – Lava that hardens on the surface. The rock layers below an extrusion are always older than the extrusion.

Other clues to Relative Age Clues from igneous rocks: Intrusions – Beneath the surface, magma may push into bodies of rock, cool then harden into a mass of igneous rock. An intrusion is always younger than the rock layers around and beneath it. Intrusion: Newer Rock

Other clues to Relative Age Clues From Faults: Faults – is a break in Earth’s crust. Forces inside Earth cause movement of the rock on opposite sided of the fault. A fault is always younger than the rock it cuts through.

Using Fossils to Date Rocks To date rocks geologists first give a relative age to a layer of rock at one location. Then they can give the same age to matching layers of rock at other locations. Certain fossils, called index fossils, help geologists match rock to layers. How can fossils be used to date rocks?

Trace Fossil Imprint: soft part such as a leaf or feather. Trace: such as a footprint Found in sediment, made up of small loose pieces of rock or sand. Sedimentary rock: rock formed from layers of compacted sediment.

Using Fossils to Date Rocks Index Fossils - are fossils that must be widely distributed and represent a type of organism that existed only briefly. Index fossils are useful because they tell the relative ages of the rock layers in which they occur. What are index fossils?

Using Fossils to Date Rocks Geologists use particular types of organisms as index fossils. For example: Trilobites were a group of hard – shelled animals whose bodies had their distinct parts. Evolved in shallow seas more than 500 million years ago. Over time, many different types of trilobites appeared. They became extinct about 245 million years ago. Trilobite fossils have been found in many places.

Using Fossils to Date Rocks You can use index fossils to match rock layers.