“The Present is the Key to the Past”

“The Present is the Key to the Past” James Hutton, 1700’s

History of Geology • The concept and measurement of geologic time has changed through human history. • Planet Earth,The Living Machine p1.mp47:15 – 8:00 • James Ussher (1581-1665) 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 • 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.

Uniformitarianism • Developed by James Hutton, advocated by Charles Lyell (1797-1875) • “The Present is the Key to the Past”, James Hutton, 1700’s • 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 1st, 2nd, etc. . . • NOT how long ago they occurred.

Laws and Principles • 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 • 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 deposition Folding

Laws 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

Laws 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. Older Younger Inclusions

Laws and Principles • Principle of Unconformities • Represents a long period during which deposition is stopped, erosion removed rock and then deposition started again. • http://www.wwnorton.com/college/geo/animations/unconformity.htm • 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. • http://www.wwnorton.com/college/geo/animations/types_of_unconformity.htm

Principle of Unconformity • Which type of Unconformity is which??? Disconformity Angular Unconformity Nonconformity

Relative Dating • Place the following layers in order of occurrence from OLDEST to YOUNGEST. Include the Fault and unconformity. 8. 7. 6. 5. 4. 3. 2. H R M Unc Fault F B I Youngest Oldest

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: • Having HARD parts • Rapid BURIAL

Fossils: Evidence of Past Life • Forms of Fossilzation • 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 Mold Cast

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-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.

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 Each Half-life: Parent goes down by ½ Daughter increases by that amount

Radiometric Dating • This can be done by Percentage too. Mathmatically, does the Daughter product EVER reach 100%? NO

Radiometric Dating • Now lets add HALF-LIFE YEARS. 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!

Radiometric 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.

Geologic 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.

Geologic Time Scale • The 4 major divisions are??? Eon Era Period Epoch

Geologic Time Scale • 88% of Earth’s 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. Visible Life Single-cell

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 Mammals Dinosaur extinction Reptiles (Dino) Marine extinction Water animals Single-cell

Geologic Time Scale Humans • Dinosaurs • Lived on Earth for 150 million years. • Humans • Lived on Earth for 100 -200 thousand years. Mammals Dinosaur extinction Reptiles (Dino) Marine extinction Water animals Single-cell

Historical Geology THE END https://www.youtube.com/watch?v=9Ra9lwKn75s

“The Present is the Key to the Past”