Transcript Chapter 3
Chapter 3 The Rock and Fossil Record Quick Write “The present is the key to the past.” This phrase was the cornerstone of the uniformitarianism theory. -write a few sentences about how studying the present could reveal the story of Earth’s history Section 1: Earth’s Story and Those Who First Listened • How did Earth come about? • Many people believe many different things. • Uniformitarianism= a principle that states that geologic processes that occurred in the past can be explained by current geologic processes. Uniformitarianism vs Catastrophism • Catastrophism is a principle that states that geologic change occurs suddenly • Ex) this would mean that mountains, canyons, seas, etc. formed during rare, sudden events • Catastrophism was what was believed for many of years until uniformitarianism proved to be more reasonable • This change in though happened around the 1830s Modern Geology A Happy Medium • During the late 20th century the uniformitarianism was challenged • the argument was that while uniformitarianism exists catastrophes do, at times, play a role in shaping the Earth • Today scientists realize that uniformitarianism nor catastrophism accounts for ALL geological changes • Most geologic changes happen over a long period of time. However catastrophes also shape the Earth. • For example, asteroids and comets form craters. QUICK WRITE • Do you think the extinction of the dinosaurs was due to uniformitarianism or catastrophism or both? Why? Paleontology • Paleontology= the study of past life • The data paleontologists use (where they get their information) are from fossils Class work: • p. 63 2-6 we will switch these and grade them together Section 2 Relative Dating: Which Came First? • Determining an object or event is older or younger than other objects or events is called relative dating • The principle of superposition states that younger rocks lie above older rocks • Look at figure 1 p.64 Disturbing forces • Not all rocks are arranged with the oldest layers on the bottom and youngest at the top • Some rock sequences are disturbed by forces within the Earth • These forces upset superposition The Geologic Column • Luckily geologists can use the geologic column to date rocks • The geologic column is combined data from all over the world of undisturbed rock sequences • The geologic column is an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth, arranged from oldest to youngest. Let’s look at the geologic column in figure 2 p. 65 How rock layers can become disturbed • • • • Fault Folding Intrusion Tilting • Look at fig 3 p66 and write the definition of each down Gaps in the Record-Unconformities • An unconformity is a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. • How unconformities are created p.67 fig 4 Types of Unconformities • Disconformities • Nonconformities • Angular Unconformities • Write a sentence about each p.68