I can: describe methods used to assign
Relative ages of rock layers Do Now: How are sedimentary rocks formed? Which fossil is the index fossil From the picture below? Index Fossils: Fossils that are found in many places; lived for a short period of time; found in only one rock layer By comparing index fossils in various locations on Earth, it is possible to correlate (match) the relative ages of the rocks in which they appear SUPERPOSITION -The bottom rock layer is the oldest and the top layer is the youngest -Sequence of rock is a record of past events
-Rock layers are ALWAYS laid down horizontally, until activities change them Relative Age of rocks: (sequence)
The age of a rock layer in comparison to its surrounding layer -Uses rock similarity, and fossil evidence What is Correlation? When geologists try to match rock layers in different locations to see if they formed at the same time. How to correlate (match) rock layers: Similarity of rock types Matching index fossils Relative Age of rocks: (sequence)
25 miles apart 1 2 3 4 5 6 1 2 3 4 5 I can: Explain how unconformities
cause gaps in rock layers Do Now: What is relative age? How can you find the relative age of rocks? Relative Age of rocks: (sequence)
25 miles apart Are we able to match up all of the layers? 1 2 3 4 5 6 1 2 3 4 5 Why? Unconformities -gaps in the rock layers
-occur when some rock layers are missing -three types WHY DOES THIS HAPPEN? Angular Unconformity horizontally parallel rock layers are deposited on tilted and eroded layers 2. Disconformity Occurs between parallel layers of sedimentary rocks that have eroded and new layers have deposited on top 3. Nonconformity Occurs between sedimentary rocks and metamorphic or igneous rocks When sedimentary rock was deposited on top of eroded metamorphic or igneous rock. What type of unconformity is it? What type of unconformity is it? I can: determine the relative age of Rock layers
Do Now: HW-Worksheet from webpage What type of unconformity is it? Nonconformity Sedimentary rocks Metamorphic rocks What type of unconformity is it?
Disconformity What type of unconformity is it?
Angular Igneous Extrusions & Intrusions
When molten rock flows on the Earths surface forming an igneous rock Intrusion: Occurs when magma squeezes between rock layers beneath the Earths surface Folds and Faults are always younger than the original
rock layers Fold: -bends in rock layers produced by movements of the earths crust Faults: -breaks in the rock where rock layers have shifted (earthquakes) UNIFORMITARIANISM: -The activities that shape the Earth today are the same activities that occurred in the past The present is the key to the past- James Hutton I can: identify how absolute age Differs form relative age
Do Now: HW-take home test How is an igneous extrusion different from an igneous intrusion Igneous extrusion is when magma reaches the surface Igneous intrusion is when magma stays beneath the surface Relative Age of rocks: (sequence)
The age of a rock layer in comparison to its surrounding layer -Uses rock similarity, and fossil evidence Absolute Age of rocks: (true age) The age of a rock layer in years -Uses radiometric dating to determine age--radioactive decay Vocabulary Review Matter is anything that takes up space and has mass
Atoms smallest unit of matter (stuff that matter is made of) -they have protons, neutrons, and electrons Element specific kind of atom with a given number of protons Vocabulary Review Matter - water Atoms Hydrogen and Oxygen atoms
Elements Hydrogen has 1 proton Oxygen has 16 protons Isotope Same element Different number of neutrons Absolute age of rock layers
Radioactive decay is the natural breakdown of atoms of an element that changes that elements atoms into a new element Example: it takes 4.5 billion years for uranium 238 to change into lead 206 Radioactive decay is NOT AFFECTED by temperature (heat) or pressure!
occurs at a constant rate known as half-life. HALF-LIFE: Half-life is the rate (time) it takes for one-half of the amount of original material to decay If we know the half-life of a radioactive material, the age of the material can be determined by measuring the amount of decayed material in the sample. Some radioactive substances have a
Short half-life: Carbon 14 decays to Nitrogen 14 -Good for dating recent organic remains (between 1,000-50,0000 yrs.) 238 206 Uranium decays to Lead Long half-life: Uranium238 -Good for dating much older rocks (a very long half-life) - it takes 4.6 billion years for uranium to decay to lead Example: The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount of Carbon-14 was 2.0 grams. (2.0g _____ _____) 1.How many half-lives did the sample undergo? 2.Multiply this by the half-life for Carbon-14 (5,700 years) Example: The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount of Carbon-14 was 2.0 grams. (2.0g 1.0g 0.5g) 1.How many half-lives did the sample undergo?2 half-lives 2.Multiply this by the half-life for Carbon-14 Answer: 2 x 5,750 = 11,500 yrs.