GEOLOGIC TIME DAY 1 October 19

Objectives 10/19 Today I will be able to: - Compare the different ways to establish relative dating - Use the principle of uniformitarianism to infer the processes that shaped the earth

Key Points 10/19  You can find evidence of past life in ______________ rocks.  The principle of ____________________________ states that the physical, chemical, and biological laws that operate today have also operated in the past.  According to the principle of cross-cutting relationships, an intrusive rock body is ______________ than the rocks it intrudes.  If a layer of sandstone is in contact with a mass of granite that contains small pieces of sandstone, the sandstone is ______________.  An ______________ is a gap in the rock record.  ______________ fossils allow geologists to match rocks of the same age in different regions.

12.1 Discovering Earth’s History ______________ ______________ ______________ Rocks record ______________ events and ______________ ______________ of the past - Particularly in ______________ rocks - We have learned that Earth is much ______________ than anyone had previously imagined and that its surface and interior have been changed by the same geological processes that continue today.

12.1 Discovering Earth’s History  ______________ means that the forces and processes that we observe ______________ have been the same ones that were at work in the ______________ and have been at work for ____________________________

12.1 Discovering Earth’s History  How old are things on Earth?  Relative dating tells us the ______________ in which events occurred, but not ______________ ______________ they occurred. Ex: Miss B is younger than Mrs. Olsen

12.1 Discovering Earth’s History  Relative Dating Methods  Law of Superposition- in an un- deformed sequence of sedimentary rocks, the ______________ layer is the ______________ and ______________ is on ______________.

12.1 Discovering Earth’s History

 Relative Dating Methods  The Principle of Original Horizontality- layers of ______________ are generally deposited in a ______________ position. If the layers are not horizontal, the force that moved them came AFTER the layers formed.

12.1 Discovering Earth’s History

 Relative Dating Methods  The Principle of Cross-Cutting Relationships- when a fault cuts through rock layers OR when magma intrudes other rocks, the fault or intrusion is ______________ than the rocks affected.

12.1 Discovering Earth’s History

 Relative Dating Methods  Inclusions are rocks within other rocks  Rocks containing inclusions are ______________ than the inclusions they contain Ex: a sample of granite that contains bits of sandstone within it. The sandstone = ______________ The sandstone is ______________

12.1 Discovering Earth’s History

 Unconformities- ______ in the ______________ record

12.2 Fossils: Evidence of Past Life  Fossils are the ______________ ______________  Found in ______________ rocks  Type of fossil is determined by the conditions under which the organism ______________ and how it was ______________

12.2 Fossils: Evidence of Past Life  Types of fossils  ______________ Remains- have not changed over time Ex: teeth, bones, shells  ______________ Remains- have changed over time Ex: Petrified (turned to stone), molds and casts, carbonization  Conditions favoring preservation of past life 1. ______________ burial 2. Possession of ______________ parts

12.2 Fossils: Evidence of Past Life  What clues about the past do fossils provide?  Indirect Evidence of Life Give us a clue about the life form without actually seeing it ______________ like ______________  ______________ allow geologists to match rocks of the same age in different regions

12.2 Fossils: Evidence of Past Life

 Types of Fossilization

Dating with Radioactivity  Radioactivity is the process by which atomic nuclei ______________  Atoms and Isotopes  Atomic number = ______________  Mass number = _______+ __________  Isotopes = same number of ______________, different number of ______________, and different atomic ______________

12.3 Dating with Radioactivity  Half-life: the time it takes for ______________ of the nuclei to decay to a ______________ ______  Original sample present after each half-life # of Half LivesRatio of Parent: Daughter

12.3 Dating with Radioactivity How much of the parent material is left after 1 half life? How about after 2 half lives? If 1/32 of the parent material remains, how many half lives have passed? How about 1/16?

12.3 Dating with Radioactivity  Why do half-lives matter?  Scientists use half lives to determine exactly how old something is.  Radiometric dating (using radioactivity) is the procedure of calculating the ______________ age of rocks