3-28-12 How do we determine a sequence of events for rock layers? Do Now: What is original horizontality, superposition, and uniformitarianism? What is contact metamorphism? Take out your review book, a piece of paper, and a PENCIL HW: R&H 278-282 A&E 1-20

Exceptions to Superposition Overturned folds or thrust faults can upset the law of superposition. (The oldest rock layers are no longer on the bottom). Rocks layers usually fold before they fault After this slide draw a cross section which highlights intrusions, extrusions, inclusions, faulting mineral veins, contact metamorphism, superposition

New Terms Inclusion – a body of older rock inside an intrusion which did not melt when the intrusion formed Cross Cutting –Cross cuts are always younger then the rock they cut through. (Faults, Intrusions, Veins) Unconformities - buried erosional surfaces which show that there are rocks missing (or a gap) from the record.

Correlation of Rock Layers (p.281) Lateral Continuity – sediments are initially deposited in a horizontal fashion extending out in all directions Exposed bedrock is called an outcrop Index Fossil – a fossil used to help date rock age. Must have existed over a wide area for a short period of time Volcanic Ash and Meteorite Deposits – can be used to date rock age based on the same requirements as index fossils

Aim: Using the ESRT to interpret Geologic History 4/6/11 Do Now: Complete Question 1 on your worksheet. What is an inclusion What are the two aspects of a good index fossil HW: R&H 284-286 A&E 21-36

Aim: How do we give rocks Absolute Ages? 4/7/11 Do Now: Finish questions on the ESRT Practice Worksheet from yesterday. HW: R&H 288-290 A&E 37-46

Radioactive Decay An element is any substance consisting of atoms which are chemically alike Elements can have heavier versions called isotopes Isotopes are unstable and decay into different elements overtime

Half Life The time it takes for half the atoms in an isotope to turn into a stable element Different isotopes have different half lives

Radioactive Dating You can use the ratio of original isotope to disintegration product to estimate the absolute age of a rock Rocks with shorter half lives are used to date more recent events and vice versa Carbon 14 can date fossils and rocks up to 50,000 years old

Aim: How have Earth’s environment and Life on Earth changed over time? Do Now: Half Life Worksheet Can anything effect the rate of a half life? Take out review books HW: R&H 291-295 A&E 47-52 (Lab if Lab Day)

Crash Course in Evolution The first life on Earth occurred about 4 billion years ago Because of chemical mutations, sexual reproduction, and a many other reasons all life has variation The environment acts on these variations and selects organisms with the best traits for that environment (Natural Selection – THERE IS NO PURPOSE TO EVOLUTION) Over time this selection changes the way a given set of organisms will look and behave and this selection can create new types of organisms.

Lets Look at the ESRT to see how the Earth and Life have changed over time Some things to keep in mind: Fossils give us evidence about Earth’s past environment Plate Tectonics have caused changes in Earth’s environment globally and locally Evolution is rapid after an extinction event