5 Can you infer who is older? Relative Time – determination of the age of a rock or geologic event by comparing with other rocks/geologic eventsCan you infer who is older?He is
6 3 Ways to DetermineRelative Time………?Coming Right Up!!
7 Law of Superposition Top = youngest layer In undisturbed sedimentary rock or lava flowsIn undisturbed sedimentary rock or lava flows:Top = youngest layerBottom = oldest layer
8 Law of Cross-Cutting Relationships Any feature that cuts across a rock or layer of sediment is younger than the rock or layer it cutsyoungest layer
9 Example of Cross-Cutting Intrusion - igneous rock that forms when magma squeezes between existing rock and hardensIntrusion - igneous rock that forms when magma squeezes between existing rock and hardens
10 Example of Cross-cutting Examples of Cross-CuttingExtrusion - igneous rock that forms when lavaflows on Earth’s surface and hardens
11 Example of Cross-cutting Example of Cross-cutting Inclusion - pieces of older rock trapped within younger rock
12 Examples of Cross-Cutting Faults, joints, tilts, and veins also follow thelaw of cross--cutting relationships
13 Law of Included Fragments Sediments are older than the cementand rock they are part ofThe pebble is older than the conglomerate rock it is found in.
26 Absolute Time – finding an exact date for rocks or geologic events in YBP (years before present) Born 2004 or1 YBPBorn 1922 or83 YBP
27 How do geologists measure Absolute Time?Radioactive Decay2. Biological Clocks - Tree rings, coral growth rings, glacial lake layers of sediment
28 Before you measure ABSOLUTE TIME you must understand the following terms…..
29 ISOTOPES- alternate forms of an element- some are RADIOACTIVE
30 Radioactive isotope - an isotope that undergoes radioactive decay Radioactivityrelease of high-energy particles from unstable atoms, maybe cancer-causingRadioactive isotope - an isotope that undergoes radioactive decay- used to determine absolute ageExamples:Uranium 238 and Carbon 14
31 Uranium - 238 Radioactive Isotope Radioactive Decay radioactive isotopes give off radioactive particles until they become stable isotopes (new elements)Example:Uranium Radioactive IsotopeRadioactive DecayLead Stable Isotope
32 Half - Life Let’s look at the half - life of Uranium 238 Amount of time it takes 1/2 the atoms in a given sample to go through radioactive decay is called it’sHalf - LifeLet’s look at the half - life of Uranium 238
36 Half-Lives of Special Isotopes Uranium Lead 2064.5 x 109 years(4,500,000,000 years)Carbon Nitrogen 145.7 x 103 years(5,700 years)
37 Unknown Radioactive Isotope. half - life = 3000 years Unknown Radioactive Isotope half - life = 3000 years sample size = 200 g Let’s complete the table below.Half LifeRemaining Unknown Radioactive Isotope (g)Number of Years20012345300010050600025900012.512,0006.2515,000
38 MASS OF UNKOWN (G) DECAY TIME (YEARS) NOW LET’S GRAPH THE HALF-LIFE OF THE UNKNOWN200100MASS OF UNKOWN (G)0 Half - Lives1 Half - Life2 H - L343000600090001200015000DECAY TIME (YEARS)
39 Remaining Radioactive C14 (g) Carbon half - life = 5,700 years sample size = 800 g Complete the following table.Half LifeRemaining Radioactive C14 (g)Number of Years800123454005,70020011,40010017,1005022,8002528,500
40 MASS OF C14 (G) DECAY TIME (YEARS) NOW LET’S GRAPH THE HALF-LIFE OF CARBON 148004000 Half - LivesMASS OF C14 (G)1 Half - Life2345,70011,40017,10022,80028,500DECAY TIME (YEARS)
41 Absolute Time vs. Relative Time Most geologists use relative time because it’s- less expensive- easier to do
43 Fossils the remains of plants and animals that lived in the past mainly formed in sedimentary rock
44 Fossils Form in Several Ways 1. Original remains - unchanged remains of a plant or animalEx. Dinosaur bones/teeth2. Replaced remains - soft parts of original animal replaced by mineralsEx. Petrified wood
45 Fossils Form in Several Ways 3. Mold - fossilized shell or bone dissolves and leaves a hollow depression in a rockEx. Ferns, leaves, or fish4. Cast - new mineral material fills a moldEx. Shellfish
46 Fossils form in Several Ways 5. Trace fossils - fossil evidence of animal movementEx. Trails, footprints, burrows & borings
47 Evolution - process of change that produces new life forms over time - fossils provide evidence of evolution
48 Natural Selection theory of evolution best adapted organisms will survive in large numbers and pass on these adaptations to their offspring
49 Index Fossils Index fossils must: 1. Be recognizable 2. Widespread - special fossils that give the relative age of the rocks that contain themIndex fossils must:1. Be recognizable2. Widespread3. Exist for a short time
50 Key Bed- single rock layer that is recognizable, widespread, and exists for a short time
51 Correlation - matching rock layers from one area to another This can be done in several ways:1. “Walking the outcrop”2. Matching similar rock features3. Index fossils
52 Correlating or matching index fossils from three outcrops.
53 Correlate the 3 rock sequences to make a single rock column for the geologic history of the region. (oldest on bottom)
55 Correlation means “to match” Geologists match all of the following: No place on the earth has all the rocks formed through time. So geologists use correlation to make a single rock column that shows the entire history of the earth.Correlation means “to match”Geologists match all of the following:rock typesrock sequencesash layers from volcanic eruptionsindex fossils
63 # of protons + # of neutrons Isotopes - different forms of the same element- normal # of protons- more than normal # of neutrons# of protons + # of neutrons# of protonsNormal Hydrogen1 proton0 neutrons1 electronIsotope of Hydrogen1 proton1 neutron1 electron
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