Presentation on theme: "The Present is the Key to the Past James Hutton, 1700s."— Presentation transcript:
The Present is the Key to the Past James Hutton, 1700s
History of Geology The concept and measurement of geologic time has changed through human history. Planet Earth,The Living Machine p1.mp4 7:15 – 8:00 Planet Earth,The Living Machine p1.mp4 James Ussher ( ) in Ireland – calculated the age of Earth based on recorded history and genealogies in Genesis he 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.
Catastrophism – proposed by Georges Cuvier ( ) – Huge catastrophies caused major changes to Earths 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.
Uniformitarianism Developed by James Hutton, advocated by Charles Lyell ( ) The Present is the Key to the Past, James Hutton, 1700s What 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
NeoCatastrophism 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 dinosaurs Asteroid collision, Gamma-ray Bursts...
Relative Dating This is not about dating your sister!! Tells us the sequence in which events occurred in a rock. – Which formed 1 st, 2 nd, etc... – NOT how long ago they occurred.
Laws and Principles 1.Law of Superposition In an undisturbed sedimentary rock, each bed is older than the one above it and younger than the one below it. Youngest Oldest
Laws and Principles 2.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. 1.What happened first? 2.What happened second? Horizontal deposition Folding
Laws and Principles 3.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
Laws and Principles 3.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. Older Younger Inclusions
Laws and Principles 4.Principle of Unconformities – Represents a long period during which deposition is stopped, erosion removed rock and then deposition started again. – Angular unconformity – The first layers were tilted before the deposition started again. Disconformity – When two layers of sedimentary rock are separated by an erosional surface but are still parallel to eachother. Nonconformity – Erosional surface separates older igneous rocks from younger sedimentary rocks. – unconformity.htm unconformity.htm 4.Principle of Unconformities – Represents a long period during which deposition is stopped, erosion removed rock and then deposition started again. – Angular unconformity – The first layers were tilted before the deposition started again. Disconformity – When two layers of sedimentary rock are separated by an erosional surface but are still parallel to eachother. Nonconformity – Erosional surface separates older igneous rocks from younger sedimentary rocks. – unconformity.htm unconformity.htm
Principle of Unconformity Disconformity Angular Unconformity Nonconformity Which type of Unconformity is which???
Relative Dating Place the following layers in order of occurrence from OLDEST to YOUNGEST. Include the Fault and unconformity H R M Unc Fault F B I Oldest Youngest
Fossils: 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.
Fossils: Evidence of Past Life The two conditions necessary for the formation of fossils is: 1.Having HARD parts 2.Rapid BURIAL
Fossils: Evidence of Past Life Forms of Fossilzation 1.Mold and Cast – Mold: the hollow shape of the organism left after water dissolved the hard part (shell) – Cast: the solid COPY of the shape of the organism Cast Mold
Fossils: Evidence of Past Life Other forms: – Petrified: Minerals replace all or part of the organism. Shows interior detail (Quartz) Ex: Petrified Wood – Carbon 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 organism – Trace Fossils: clues that an organism was there. (Foot prints)
Fossils: Evidence of Past Life Fossil Succession – Fossils succeed one another in a definite order. (Simpler organisms = older rocks) – Any time-period can be recognized by its fossil content. Jurassic Period
Laws and Principles Fossil Correlation – Matching similar rock types found in different areas. – Index fossils: Fossils that are Widely distributed Lived a short time
Rock Correlation with Fossils Activity Answer Key Unconformity
Radiometric 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.
Radiometric Dating – Occurs in IGNEOUS rocks. – The RATE OF DECAY is CONSTANT! – Scientists use that rate to determine AGE of a rock.
Radiometric Dating Half-Life – The time it takes for half of the radioactive atoms to decay into another element. Parent material = Radioactive Element Daughter product = the stable element the radioactive element decays into. – Example: Carbon 14 turns into Nitrogen 14 Carbon 14 = Parent material Nitrogen 14 = Daughter product Carbon-14s half-life is 5,730 years. (what does that mean?) It takes 5,730 years for half of C14 atoms to decay into N14.
Radiometric Dating Potassium 40 – Argon 40 Dating (K Ar) (Beta capture) – Parent = Potassium 40 Daughter = Argon 40 – Half-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.
Carbon-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
Radiometric Dating Carbon 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.
Radiometric Dating How to determine age of rock using Half-lives Half-lifeParent elementDaughter product 010 1½1/2 2¼¾ 31/87/8 41/1615/16 Each Half-life: Parent goes down by ½Daughter increases by that amount
Radiometric Dating This can be done by Percentage too. Half-LifeParent elementDaughter product 0100%0 150% 225%75% 312.5%87.5% 46.25%93.75% Mathmatically, does the Daughter product EVER reach 100%?
Radiometric Dating Now lets add HALF-LIFE YEARS. Half-LifeParent element (C14) Daughter product (N14) 0 yrs100%0% 5730 yrs50% 11,460 yrs25%75% yrs12.5%87.5% 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? years ago!
Radiometric Dating Importance of Radiometric Dating 1.Provided dates for events in Earths History. 2.Supported beliefs of James Hutton, Charles Darwin and others who said Earth is VERY OLD. 3.There has been enough time for major changes to have occurred geologically.
Geologic Time Scale Earth = 4.6 Billion years old (byo) – Earths 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.
Geologic Time Scale The 4 major divisions are??? 1.Eon 2.Era 3.Period 4.Epoch
Geologic Time Scale 88% of Earths History – PreCambrian Very little evidence of life. Other 12% – Phanerozoic Sudden development of life in the oceans. Hard parts developed which increased the fossil record. Single-cell Visible Life
Geologic Time Scale Eras (Divided by major extinctions) – Paleozoic (Hard parts developed) Marine animals thrived Pangaea formed Extinction – 90% of marine animals became extinct. – Mesozoic Dinosaurs developed Pangaea began to break up. Extinction – Dinosaurs – Cenozoic Mammals became dominant Humans evolved Marine extinction Water animals Single-cell Reptiles (Dino) Mammals Dinosaur extinction
Geologic Time Scale Dinosaurs – Lived on Earth for 150 million years. Humans – Lived on Earth for thousand years. Marine extinction Water animals Single-cell Reptiles (Dino) Mammals Dinosaur extinction Humans
Historical Geology THE END https://www.youtube.com/watch?v=9Ra9lwKn75s