Absolute Dating: Grab a book and read pages and answer the prelab questions Radiometric dating

How do they measure the ACTUAL age of rock?

Count Tree rings Dates trees back to 8000 years

In the summer when glaciers melt and retreat, sediment in the center of large glacial lakes is deposited in annual layers called varves Dates back to the last glacial ice age 15,000 yrs. ago Count the layers

Radiometric dating of rocks Marie Curie 1900’s Discovered all Rocks have Radioactive isotopes: unstable atoms that decay, release energy and change into different element over a specific period of time Half-life – the time for half of the radioactive nuclei to decay

Each radioactive element has it’s own fixed half-life. Each decays at a predictable, regular RATE

Rubidium-8747 billion years Potassium billion years Radiometric dating can be done, but only reliably on IGNEOUS ROCKS and volcanic ash

5. Carbon-14 dating All living things contain carbon Carbon-14 is the radioactive form (“evil twin”) of carbon- 12 It’s half-life decay rate is 5730 years. Organic materials less than 70,000 yrs old can be dated this way.

The radioactive decay curve First half life 2 nd half life “Parent” is the radioactive isotope that decays “Daughter” is new atoms that have formed from the decay of the parent Half-life time is constant

Practice A radioactive isotope has a half-life of 10,000years. The percent of parent atoms left is 25% How OLD is the rock containing the radioactive material? 1 half-life = 50% remains, age of rock is 10,000 years old 2 half-life = 25% remains rock is ANOTHER 10,000 yrs. old So……. 20,000 years old!

Radioactive Half-life (Candy) Lab Parent isotope Total Number decayed Start # of atoms st half life 2 nd half life 3 rd half life Percent Parent remaining Age of rock 100% ________ % % % If the half life of this radioactive isotope was 3000 years, how old is this rock? 3000 yrs old 6000 yrs. Old 9000 yrs. old

Directions: determine the AGE of your rock using radioactive atoms in the rock 1.Remove any “mutant” atoms that do not have a letter on them. 2.Put radioactive “parent” atom’ in the box facing UP. 3.Count the number of atoms to start. Record on data table 4.Put lid on and gently toss to decay the atoms. 5.Remove the “daughter” atoms that have ‘flipped over’ (decayed). Count and record the number of remaining atoms in the box. 6.Continue until all the atoms have ‘decayed’ 7.Determine the age of your rock using the half-life time.

Make your prediction Half-lives that have occurred Predict The # of “parent” (radioactive) atoms that will remain after the next half-life (shake) Actual # of “parent” (radioactive) atoms that REMAINING in the box after the half-life (shaking) Percent % of “parent” atoms remaining Age of your rock % Half-life of the rock is _____200_____________ years

Dating sedimentary strata using radiometric dating Figure Which type of rock has been dated: Igneous, sedimentary of metamorphic? How old is the Dakota Sandstone? How old is the Wasatch Formation?

FBKNAJDMHCLGEFBKNAJDMHCLGE 425 my 300 my How old are layers D and J?

Number of half-lives Ratio of Parent to daughter (radioactive) : (stable) atoms Percent of parent remaining 01:0 100% :1 50% 1:3 25% 1:7 13% 1:15 6%

1) How does Sedimentary Rock form? 2) What are the 3 types of Sedimentary rock? 3) How can you distinguish between the 3 types of sedimentary rock? Clastic rocksNON-Clastic ChemicalOrganic rock Hint: They can all form in water!

Because sediment is sorted by size in water Particle Size determines Environment that the rocks would be found Boulders, cobbles, gravel moved by swiftly flowing water, rockslides or glaciers River beds, Sand moved by rivers, streams, windblown, Edges of lakes, oceans Beaches dunes, Silt / clay found in quiet waters, lake BOTTOMS, lagoons, swamps, ponds

2. Chemical Sedimentary Rocks (pg. 129) Step 1. Begins with… Step 2. Then the water… Examples: - Minerals (chemicals) that are dissolved in sea, water, lakes, underground Evaporates and the minerals precipitate out Rock salt Gypsum limestone

Organic Sedimentary rock Step 1. Begins in swamps with…. Remains of living things: plants and animals, shells Organic material that contain carbon. Step 2. In swamps, they material doesn’t decompose Compressed (without oxygen) Bituminous coal

A B C D QUIZ: For each Clastic Rock. Name it, Identify where it is made, and what sediments it is made from.

Describe the Features of Sedimentary rocks Stratification Ripple marks, mud cracks Fossils Geodes Sedimentary rocks Pg.130

Bellringer: Match the following: a.Leaf print in shale b. Mammoth tusk c. Rabbit burrow d. carbon print of fish e. Petrified wood 1.Original remains 2.Replaced remains 3.Molds / casts 4.Trace fossils 5.Carbonaceous films

4. Write the letters that the rock formed in order. Quiz 1.What is an Index Fossil? Why are they important? 2.What are the three major Eras of Geological Time? 3.Tell the story of how the Sedimentary Rock formed below using terms like deposition, strata, folding, erosion, and unconformity. F E D C A B G

First….. A B C Layers A,B,C, were laid down in succession. Layer A was deposited first, then B, then C.

Then they were uplifted and folded

Then glaciers moved through eroded the top

Then new layers of sediment were deposited on top at different times

Geologic time scale  Subdivisions of Eons Era Eras of the Phanerozoic eon Cenozoic (“recent life”) Mesozoic (“middle life”) Paleozoic (“ancient life”) Eras are subdivided into periods Periods are subdivided into epochs Overview song

Figure The Geologic Time Scale om/watch?v=j2r55qC PbDo

Quia Matching Columns Activity On Geological Time