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 oflife/fossils/ oflife/fossils/ em/geologictime/ em/geologictime/