Presentation on theme: "“The Present is the Key to the Past”"— Presentation transcript:
1“The Present is the Key to the Past” James Hutton, 1700’s
2History of GeologyThe concept and measurement of geologic time has changed through human history.Planet Earth,The Living Machine p1.mp4 7:15 – 8:00James Ussher ( ) in Irelandcalculated the age of Earth based on recorded history and genealogies in Genesishe said that Earth was created on October 22, 4004 B.C.it was considered heresy to say Earth was more than about 6000 years old.
3Catastrophism Catastrophism proposed by Georges Cuvier (1769-1832) Huge catastrophies caused major changes to Earth’s geology and biology in a short period of time.six major catastrophes occurred, corresponding to the six days of biblical creation, the last one was the biblical flood.
4UniformitarianismDeveloped by James Hutton, advocated by Charles Lyell ( )“The Present is the Key to the Past”, James Hutton, 1700’sWhat happens today is what happened in the past.Earth changes very slowly.Supports a very old age of Earth.Earth is believed to be about 4.6 billion years old
5NeoCatastrophism Blends Uniformitarianism with some Catastrophism. Earth developed and changed at a very slow rate like today, but had some catastrophic event s that caused some sudden changes.Eg: extinction of dinosaursAsteroid collision, Gamma-ray Bursts . . .
6Relative Dating This is not about dating your sister!! Tells us the sequence in which events occurred in a rock.Which formed 1st, 2nd, etc. . .NOT how long ago they occurred.
7Laws and Principles Law of Superposition Youngest Oldest In an undisturbed sedimentary rock, each bed is older than the one above it and younger than the one below it.YoungestOldest
8Laws and Principles Principle of Original Horizontality Layers of sediment are generally deposited in a horizontal position.Rocks that are folded or tilted must have been moved into that position AFTER their formation.What happened first?What happened second?Horizontal depositionFolding
9Laws and Principles Principle of Cross-Cutting Relationships When a fault or igneous intrusion cuts through another rock,the fault or intrusion is YOUNGER than rock it cut through.Igneous Intrusion
10Laws and Principles Principle of Inclusions Inclusions are pieces of one rock found in another.The rock containing the inclusions is YOUNGER than the rock the inclusions came from.OlderYoungerInclusions
11Laws and Principles Principle of Unconformities Represents a long period during which deposition is stopped, erosion removed rock and then deposition started again.Angular unconformityThe first layers were tilted before the deposition started again.DisconformityWhen two layers of sedimentary rock are separated by an erosional surface but are still parallel to eachother.NonconformityErosional surface separates older igneous rocks from youngersedimentary rocks.
12Principle of Unconformity Which type of Unconformity is which???Disconformity Angular Unconformity Nonconformity
13Relative DatingPlace the following layers in order of occurrence from OLDEST to YOUNGEST. Include the Fault and unconformity.220.127.116.11.4.3.2.HRMUncFaultFBIYoungestOldest
14Fossils: Evidence of Past Life What is a Fossil?Preserved remains or traces of prehistoric life.The type of fossil formed is determined by the conditions the organism died and was buried.
15Fossils: Evidence of Past Life The two conditions necessary for the formation of fossils is:Having HARD partsRapid BURIAL
16Fossils: Evidence of Past Life Forms of FossilzationMold and CastMold: the hollow shape of the organism left after water dissolved the hard part (shell)Cast: the solid COPY of the shape of the organismMoldCast
17Fossils: Evidence of Past Life Other forms:Petrified: Minerals replace all or part of the organism. Shows interior detail(Quartz) Ex: Petrified WoodCarbon Films: A thin coating of carbon on the rock. The carbon is left from the organism itself. (plants and insects)Impressions: a copy of the surface of organismTrace Fossils: clues that an organism was there. (Foot prints)
18Fossils: Evidence of Past Life Fossil SuccessionFossils succeed one another in a definite order. (Simpler organisms = older rocks)Any time-period can be recognized by its fossil content.Jurassic Period
19Laws and Principles Fossil Correlation Index fossils: Fossils that are Matching similar rock types found in different areas.Index fossils: Fossils that areWidely distributedLived a short time
20Rock Correlation with Fossils Activity Answer KeyUnconformity
21Radiometric Dating Radioactive Elements Unstable elements break down or DECAY.Occurs when the Nucleus changes (Protons and Neutrons change).During Radioactive Decay, one element breaks down into another element giving off ENERGY.
22Radiometric Dating Occurs in IGNEOUS rocks. The RATE OF DECAY is CONSTANT!Scientists use that rate to determine AGE of a rock.
23Radiometric Dating Half-Life The time it takes for half of the radioactive atoms to decay into another element.Parent material = Radioactive ElementDaughter product = the stable element the radioactive element decays into.Example: Carbon 14 turns into Nitrogen 14Carbon 14 = Parent materialNitrogen 14 = Daughter productCarbon-14’s half-life is 5,730 years. (what does that mean?)It takes 5,730 years for half of C14 atoms to decay into N14.
24Radiometric DatingPotassium 40 – Argon 40 Dating (K Ar) (Beta capture)Parent = Potassium Daughter = Argon 40Half-life = 1.3 billion years.Can be used to date rocks because of its long half-life.Why do you need a LONG half-life to date rocks?Because rocks are old so if half-life is short, there will be NO Parent element in the rock, only the Daughter product. You need Both to determine age.
25Carbon-14 Nitrogen-14 Cycle All living things have C-14 in them.This begins to turn to N-14 the moment they die.Can only be used for dating if there is some C14 remaining in the organism
26Radiometric DatingCarbon 14 – Nitrogen 14 (C14 – N14): (Beta emission)Called Carbon Dating.Only used for dating things ONCE LIVING.Decay begins when the organism dies.Only works for things YOUNGER than 75,000 yrs.Iceman found in in the European Alps. He died 53,000 years ago.
27Radiometric Dating How to determine age of rock using Half-lives Half-lifeParent elementDaughter product11/2231/87/841/1615/16Each Half-life: Parent goes down by ½ Daughter increases by that amount
28Radiometric Dating NO This can be done by Percentage too. Half-LifeParent elementDaughter product100%150%225%75%312.5%87.5%46.25%93.75%Mathmatically, does the Daughter product EVER reach 100%?NO
29Radiometric Dating 17190 years ago! Now lets add HALF-LIFE YEARS. Parent element (C14)Daughter product (N14)0 yrs100%0%5730 yrs50%11,460 yrs25%75%17190 yrs12.5%87.5%22920 yrs6.25%93.75%So if we measured a sample of a mummy and found it to be 12.5% C14 and 87.5% N14, how long ago did he die?17190 years ago!
30Radiometric Dating Importance of Radiometric Dating Provided dates for events in Earth’s History.Supported beliefs of James Hutton, Charles Darwin and others who said Earth is VERY OLD.There has been enough time for major changes to have occurred geologically.
31Geologic Time Scale Earth = 4.6 Billion years old (byo) Earth’s time span is SOOOO GREAT, that scientists have divided it into smaller units of time making the “Geologic Time Scale”.This division of time helps people grasp this expanse of time.Scientists used changes in major life-forms and extinctions to divide the time scale.The division of the time scale is broken into 4 sections.
32Geologic Time ScaleThe 4 major divisions are???EonEraPeriodEpoch
33Geologic Time Scale 88% of Earth’s History Other 12% PreCambrian Very little evidence of life.Other 12%PhanerozoicSudden development of life in the oceans.Hard parts developed which increased the fossil record.Visible LifeSingle-cell
34Geologic Time Scale Eras (Divided by major extinctions) Paleozoic (Hard parts developed)Marine animals thrivedPangaea formedExtinction90% of marine animals became extinct.MesozoicDinosaurs developedPangaea began to break up.DinosaursCenozoicMammals became dominantHumans evolvedMammalsDinosaur extinctionReptiles (Dino)Marine extinctionWater animalsSingle-cell
35Geologic Time Scale Dinosaurs Humans Lived on Earth for million years.HumansLived on Earth for thousand years.MammalsDinosaur extinctionReptiles (Dino)Marine extinctionWater animalsSingle-cell