Transcript CH 8 SEC 2
CH 8 SEC 2 THE RELATIVE AGE OF ROCKS GOAL/PURPOSE • STUDENTS KNOW THAT THE ROCK CYCLE INCLUDES THE FORMATION OF NEW SEDIMENT AND ROCKS ARE OFTEN FOUND IN LAYERS WITH THE OLDEST Generally AT THE BOTTOM. THERE ARE 2 WAYS TO EXPRESS AGE • RELATIVE AGE- OF A ROCK IS ITS AGE COMPARED TO OTHER ROCKS. • EX- YOU ARE OLDER THAN YOUR SISTER BUT YOUNGER THAT YOU BROTHER • ABSOLUTE AGE- OF A ROCK IS THE NUMBER OF YEARS SINCE THE ROCK WAS FORMED. DIFFICULT TO EXACTLY KNOW BUT CAN COME CLOSE. POSITION OF ROCK LAYERS • 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.. LAW OF SUPERPOSITION DETERMINING Relative AGE • KEY - TO DETERMINE RELATIVE AGE, GEOLOGISTS STUDY EXTRUSIONS AND INTRUSIONS OF IGNEOUS ROCK, FAULTS, GAPS IN THE GEOLOGIC RECORD AND INCLUSIONS • EXTRUSION- LAVA HARDENS ON THE SURFACE. ALWAYS YOUNGER THAN ROCKS BELOW CONT’D • INTRUSION- BENEATH THE SURFACE MAGMA COOLS AND HARDENS INTO A MASS OF IGNEOUS ROCK. ALWAYS YOUNGER THAN ROCKS BELOW. • FAULT- IS A BREAK IN THE EARTHS CRUST • UNCONFORMITY- THE SURFACE WHERE NEW ROCK LAYERS MEET A MUCH OLDER LAYER • INCLUSION- IS A PIECE OF ROCK THAT IS CONTAINED IN ANOTHER ROCK. THE ROCK CONTAINING AN INCLUSION IS YOUNGER INCLUSIONS USING FOSSILS • INDEX FOSSIL- A FOSSIL THAT IS WIDELY DISTRIBUTED AND REPRESENT A TYPE OF ORGANISM THAT EXISTED ONLY BRIEFLY. • KEY- INDEX FOSSILS ARE USEFUL BECAUSE THEY TELL THE RELATIVE AGES OF THE ROCK LAYERS IN WHICH THEY OCCUR. INDEX FOSSIL QUESTIONS AND ANSWERS • • • • 1 ABC 2 AB 3 AB http://www.brainpop.com/science/diversity oflife/fossils/ • http://www.brainpop.com/science/earthsyst em/geologictime/