Complete the “Who Dun It” activity at your seat. Be prepared to Warm Up: Complete the “Who Dun It” activity at your seat. Be prepared to explain how you got your answers. If you have color pencils, get them out Date Session Activity Page 1/19-20 3 Who Dun It Dating Rock Layers - Superposition 4 Superposition Challenge 5 Practice…”Which Is Older?” 6 Homework: Superposition Challenge writing

Page 3 Who left: 5th 4th 3rd 2nd 1st How did you make your decision?

EQ: How do scientists determine the age of rock layers. 8. E EQ: How do scientists determine the age of rock layers? 8.E.2 Understand the history of Earth and its life forms based on evidence of change recorded in fossil records and landforms. 8.E.2.1 Infer the age of Earth and relative age of rocks and fossils from index fossils and ordering of rocks layers (relative dating and radioactive dating) 8.E.2.2 Explain the use of fossils, ice cores, composition of sedimentary rocks, faults, and igneous rock formations found in rock layers as evidence of the history of the Earth and its changing life forms

Why is this statement false: “The caveman had dinosaur for breakfast.”?

man and dinosaurs never lived at the same time…how do we know? Why is this statement false: “The caveman had dinosaur for breakfast.”? man and dinosaurs never lived at the same time…how do we know?

Superposition notes p. 4 Evidence of earths history is found in rock layers. How they are arranged, what is in those layers and any disturbances in those layers tell a story. There are three interpretations we use in determining the age and order of events in rock layers. 1. Relative age 2. Index fossils 3. Absolute age

Relative Age: Rock’s age when compared to the ages of other rocks Relative Age: Rock’s age when compared to the ages of other rocks. Layers of rock that are younger will be deposited on top of layers of rocks that are older. Fossils are the same age as the rock layer in which they are found This fossil and this rock layer are the same age Highlight the key word in the definition of relative age

Index fossils

Every fossil is NOT an index fossil Every fossil is NOT an index fossil. What characteristics must fossils have to be index fossils? Lived in a large geographic area (large horizontal distribution of the fossil) Lived for short period of time (small vertical distribution of the fossil)

Index Fossil A fossil that - widely distributed geographically (large horizontal distribution) - lived for a short period of time (small vertical distribution) Which fossil is An index fossil? How do you know? What is the scientific value of the other fossils?

Scientists can use index fossils to show that rocks or geologic events occurring at different locations are the same age. This process is known as Correlation

Absolute Age Using the half-life of a radioactive material deposited in rock layers to determine the “exact” age of the rock. Highlight the most Important word in the definition. Radioactive dating is accurate on igneous rocks, but not sedimentary. Why? Example: Uranium (U) decomposes to become lead (Pb). Its half life is 4.5 billion years. What subatomic particle is responsible for this change?

Laws of geologic history Superposition—Oldest rocks on the bottom of an undisturbed sequence of rock Original Horizontality—Sedimentary are initially deposited in flat (horizontal) layers Cross-cutting Relationships—Objects which cross-cut rocks are younger than the rocks themselves (ex: fault or intrusion) Faults are cracks caused by plate movement Intrusions are lava that melted through rock and then hardened

Superposition

Using superposition, label the strata (rock layer) below from oldest to youngest.

Superposition Challenge

Horizontality Sedimentary rock layers are originally deposited in horizontal layers

Cross-cutting relationships Faults and Intrusions are always younger than the rocks they cut through.

Which is older: F or S How do you know?

UNIFORMITARIANISM These laws are based on the assumption that the forces at work today are the same forces at work in history = uniformitarianism.

Disturbance in rock layers can be caused by….. Erosion Tectonic plate movement Volcanic activity

a buried erosional surface What is an unconformity? How does it complicate the relative dating of rock layers? a buried erosional surface a part of the rock record is missing

Using the diagram to the left, identify where the unconformity is located by drawing an arrow and writing the word “unconformity” next to it. What are the characteristics of an unconformity in a rock layer?

Superposition Challenge

Faults

A break in earth’s crust caused by earthquakes Fault: A break in earth’s crust caused by earthquakes (plate movement) Which is older A or B What are the characteristics of faults in a rock layer?

Intrusions

Lava cuts/melts through rock layers in Earth’s crust. Intrusion Lava cuts/melts through rock layers in Earth’s crust. Which is older C or B? What are the characteristics of an intrusion in a rock layer? C

Superposition Challenge

Overturning

Overturning Horizontal rock layers tilt or fold due to movement of tectonic plates.

**** Contact Metamorphism: Metamorphism due to contact with or proximity to an igneous intrusion. This helps you decide if a change in a rock layer was due to erosion (no metamorphism) or an intrusion (intense heat caused a thin layer of metamorphism around the intrusion)

“Which is Older?” For each diagram write the letter of the layer/event that is older

Complete Superposition Challenge Diagrams Superposition Extension…writing