Lesson 3 1 RelativeAge Dating Vocabulary relative age

Lesson 3. 1 Relative-Age Dating

Vocabulary relative age correlation superposition fossil inclusion index fossil unconformity

Essential Questions 1 What does relative age mean? 2 How can the positions of rock layers be used to determine the relative ages of rocks?

Explore Activity Age Before Bedrock Which of your two friends is older? To answer this question, you’d need to know their approximate ages. You wouldn’t need to know the exact age of either of your friends, just who was born first. The same is sometimes true for rock layers. Identify the order of the indicated features from oldest to youngest.

Relative Ages of Rocks Relative age is the age of rocks and geologic features compared with other rocks and features nearby.

Unconformities (t)Doug Sherman/Geofile, (c) Stephen Reynolds, (b)Fletcher & Baylis/Science Source An unconformity is a surface where rock has eroded away, producing a break, or gap, in the rock record.

Angular Unconformity

Correlation Matching rocks and fossils from separate locations is called correlation.

Evidence of the Distant Past Fossils are the preserved remains or evidence of ancient living things. Fossils form only under certain conditions.

Mini-Assessment 1. Which statement is NOT a principle of relative-age dating? A Layers of sediment are deposited horizontally. B Fossils are needed to determine the relative age of a rock. CORRECT C Sediments are deposited in large, continuous sheets. D The oldest rocks are on the bottom in undisturbed rock layers.

Mini-Assessment 2. Trilobites are used as index fossils because A they are easy to identify. B they are some of the oldest fossils. C they were abundant and lived on Earth for a short time. CORRECT D they were the only marine organism during one short period of time.

Mini-Assessment 3. What do scientists look for in order to correlate rocks in different locations? A different rock types and similar fossils C similar rock types and lack of fossils B many rock types and many fossils D similar rock types and similar fossils CORRECT

Mini-Assessment 4. Which term means matching up rock layers in different places? A correlation C inclusion horizontality D superposition CORRECT B

Mini-Assessment 5. Which sequence of letters describes the rock layers in the diagram from oldest to youngest? A D, Q, A, Z, L B L, Z, A, Q, D CORRECT C Z, L, A, D, Q D Q, D, L, Z, A

Mini-Assessment 6. Which of the following correctly describes the relative age of the fault? A younger than A, but older than Q B younger than Z, but older than L C younger than Q, but older than A CORRECT D younger than D, but older than Q