Ms. Susinno’s favorite topic Geologic History Ms. Susinno’s favorite topic Please view as a slideshow

Geologic time scale is divided based on fossil evidence. http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/mass-extinctions/end-permian-mass-extinction/

ESRt Challenge! Hint: you need many pages of the ESRT!

Meet my friend “Eury”!

The Anthropocene is a proposed geologic chronological term for an epoch that begins when human activities have had a significant global impact on the Earth's ecosystems. Do you think we should name the current epoch the anthropocene? Provide an argument based on evidence http://www.smithsonianmag.com/science-nature/what-is-the-anthropocene-and-are-we-in-it-164801414/?no-ist

Reading the geo time scale 1. What is the oldest living organism? 2. When did oxygen enter the atmosphere? 3. Explain how this might have happened. 4. How long have humans been on Earth compared to Earth’s history? 5. If Earth’s history were compared to one day (24 hours) how long do you think man would have been here?

GEOLOGIC TIME scale Geologic History

stromatolites

How and why do geologists date rocks? Geologists date rocks using: Relative age- older and younger Actual age- rock layer can be assigned a time period or definite numerical age.

Geologists make Some assumptions about strata In order to interpret rock layers: Uniformitarianism- “the key to the present is the past ”~James Hutton This idea says that Earth’s shaping processes are basically the same as they have been in the past (earthquakes, volcanoes, deposition and erosion) and can help interpret the present rock formations.

2. The principle of Original Horizontality- Sediment is usually deposited in flat layers. If it is no longer flat, something happened to it! 3. Principle of Superposition- the bottom layer of a series of sedimentary layers is usually the oldest **unless it has been overturned (from folding) or older rock has been thrust over it (from faulting)

Relative Dating

What is an unconformity? Unconformity a buried erosional surface representing a gap in the sedimentary rock record. They are usually represented by in Earth Science diagrams. What’s missing? Rock layer(s) and Time http://www.classzone.com/books/earth_science/terc/content/visualizations/es2902/es2902page01.cfm and http://www.bioygeo.info/Animaciones/Unconformity.swf to see an unconformity form.

Intrusion of 4 with contact metamorphism Oldest Deposition of layer 1 Deposition of layer 2 Deposition of layer 3 Intrusion of 4 with contact metamorphism Weathering and erosion of 3 and 4, =unconformity (an unconformity only happens if there is submergence and deposition on top, otherwise it is just an exposed erosional surface) 6. Deposition of layer 5 Youngest

List the sequence of events from oldest to youngest 1st deposition of shale 2nd deposition of sandstone 3rd deposition of limestone 4th weathering and erosion of limestone = unconformity 5th deposition of sandstone 6th igneous intrusion with contact metamorphism

Follow this example: 1.Deposition of conglomerate 2. Deposition of shale 3. Deposition of limestone 6. Igneous intrusion with contact metamorphism 4. Deposition of sandstone 7. Weathering and erosion = unconformity 5. Deposition of shale 9. Weathering and erosion of the surface 8. Deposition of sandstone How do you know the sandstone (step4) and the shale came before the intrusion?

(on the next slide) on the next slide Do not draw on your monitor 

82. Siccar Point Aug 2009

Is this relative dating or … List the sequence of events from oldest to youngest. Include time period (and range in years) for each layer. Is this relative dating or …

Actual Dating

The number of protons defines an atom. What are ISOTOPES? This is how many protons rubidium has Atoms with the same number of protons, but different numbers of neutrons. This is protons + neutrons. The number of protons defines an atom.

Isotopes are unstable and “decay” into other elements. The number of protons can change in a few different ways: When the # of protons (atomic number) changes the atom becomes a new element! Watch me to see a cartoon of radioactive decay: https://youtu.be/o-9yt7OAYmE

Radioactive Elements used in Actual dating: This is our last chart in the ESRT

Half-life- the time it takes for one half of the molecules in a sample to decay to the stable isotope. What is the half life of Carbon 14? *After about 5 half-lives, the amount of the original material is too negligible to be detected and therefore, cannot be tested.

Carbon 14 is used to date things that were once alive because when they die, they stop producing the isotope and it begins to decay to Nitrogen 14.

How many Half- lives? How much of the original left? Original:Decay Product 1 half life ½ (.5) 50% 1 part Original:1 part Decay Product 2 half lives ¼ (.25) 25% 1:3 (1 quarter : 3 quarters) 3 half lives 1/8 (.125) 12.5% 1:7 4 half lives 1/16 (.0625) 6.25% 1:15 5 half lives 1/32 (.03125) 3.125% 1:31

Original Decay Product Two half lives One half life Three half lives

b. How much carbon14 remains?   PRACTICE: Fred the poor dead fish kicked the bucket 11, 460 years ago, how many half –lives have passed? b. How much carbon14 remains? c. How much of the 14N is left after that many half- lives?

1. I found a rock that was 4.5 Billion years old. a. How much 238U remains in it? b. How many half –lives have passed? ***If I cut the rock in half, what will its half life be? c. How much of the Lead208 is left after that many half- lives?

a. How many half –lives have passed?   2. I found a rock which was 3.9 x 109 years old. How much 40K was left? a. How many half –lives have passed? b. How much of the Potassium 40 is left after that many half- lives? 3. An igneous rock contains 10 grams of 40K and 10 grams of its decay products. During which geological time interval was it formed? Middle Archaen 2. Late Archean 3. Middle Proterozoic 4. Late Proterozoic

5. According to the Earth Science Reference Tables, which radioactive element formed at the time of the Earth's origin has just reached about one half-life? carbon-14 potassium-40 uranium-238 rubidium-87 6. A sample of rock contained 100 grams of potassium-40 (40K) when it was formed. Today the rock contains 50 grams of potassium-40 (40K). According to the Earth Science Reference Tables, what is an approximate age of the rock? 1.4 x 109 years 2.8 x 109 years 4.5 x 109 years 5.6 x 109 years

Radiocarbon Dating Radioactive carbon-14 (C14), because of its short half-life, is used for the absolute dating of organic remains that are less than 70,000 years old. Carbon-14 is an isotope of carbon that is produced in Earth’s upper atmosphere. High-energy cosmic rays from the Sun hit nitrogen-14 (N14), producing radioactive C14. This C14 is unstable and will eventually change back into N14 through the process of radioactive decay. The proportions of C14 and ordinary C12 in Earth’s atmosphere remain approximately constant. Radioactive C14, just like ordinary C12, can combine with oxygen to make carbon dioxide. Plants use CO2 during photosynthesis. The proportion of C14 to C12 in the cells and tissues of living plants is the same as the proportion of C14 to C12 in the atmosphere. After plants die, no new C14 is taken in because there is no more photosynthesis. Meanwhile, the C14 in the dead plant keeps changing back to N14, so there is less and less C14. The longer the plant has been dead, the less C14 is found in the plant. The age of organic remains can be found by comparing how much C14 is still in the organic remains to how much C14 is in a living organism.  

Radioactive C14 was used to determine the geologic age of old wood preserved in a glacier. The amount of C14 in the old wood is half the normal amount of C14 currently found in the wood of living trees. What is the geologic age of the old wood? State one difference between dating with the radioactive isotope C14 and dating with the radioactive isotope uranium-238 (U238).

Up next- our last topic: The End! Helpful Links: Help w/ pgs8-9 ESRT: https://www.youtube.com/watch?v=y9LhrG5b8CM and https://youtu.be/arz-r0weWXg and https://youtu.be/5fbx4TBIZPE Half-life animation: http://www.absorblearning.com/media/attachment.action?quick=185&att=3167 How does Carbon dating work: https://youtu.be/phZeE7Att_s Unconformity animations: http://www.classzone.com/books/earth_science/terc/content/visualizations/es2902/es2902page01.cfm and http://www.bioygeo.info/Animaciones/Unconformity.swf and http://www.wwnorton.com/college/geo/egeo2/content/animations/10_4.htm Up next- our last topic: Fossils!