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

GEOLOGIC TIME scale Geologic time scale is divided based on fossil evidence. and extinction-0916 and for extinction informationhttp://news.mit.edu/2015/siberian-traps-end-permian- extinction-0916https://youtu.be/y6ig6zKiNTc end-permian-extinction-0916

The fossil Record Examination of the fossil record shows a general tendency of organisms to become increasingly more complex through geologic time. This finding supports the theory that living things have undergone evolution. The oldest known fossils, in fact, are cyanobacteria (single -celled, blue-green algae) from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old!

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. and-are-we-in-it /?no-ist Do you think we should name the current epoch the anthropocene? Provide an argument based on evidence

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 History GEOLOGIC TIME scale

stromatolites

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

1.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. Geologists make Some assumptions about strata In order to interpret rock layers:

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. and to see an unconformity form. What’s missing? Rock layer(s) and Time

Oldest 1.Deposition of layer 1 2.Deposition of layer 2 3.Deposition of layer 3 4.Intrusion of 4 with contact metamorphism 5.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

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

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

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

82. Siccar Point Aug 2009

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

What are ISOTOPES? Atoms with the same number of protons, but different numbers of neutrons. This is how many protons rubidium has 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: Watch me to see a cartoon of radioactive decay: When the # of protons (atomic number) changes the atom becomes a new element!

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.

Carbon 14 molecule How many 14 C turned to 14 N? Nitrogen 14 molecule 8/16 = ½ 50% 1 red: 1 green 1 half life! 5700 years Did the number of total molecules change? NO! So if I cut the sample in half what would happen to the C14 half life? It would remain the same! In other words, if the dino only started with 8 C14 then it would still take 5,700 to be 4 N14. GET IT? After two half lives, how much 14 C will be left? How much 14 N? 11, 400 years years 4/16 = 1/4 =25% 14 C, 75% 14 N 1 part red 3 parts green :

How many Half- lives? How much of the original left? Original:Decay Product 1 half life½ (.5) 50%1 part Original:1 part Decay Product 2 half lives¼ (.25) 25%1:3 (1 quarter : 3 quarters) 3 half lives1/8 (.125) 12.5%1:7 4 half lives1/16 (.0625) 6.25%1:15 5 half lives1/32 (.03125) 3.125%1:31

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

PRACTICE: a.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 14 N is left after that many half- lives?

1. I found a rock that was 4.5 Billion years old. a. How much 238 U 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?

2. I found a rock which was 3.9 x 10 9 years old. How much 40 K 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 40 K and 10 grams of its decay products. During which geological time interval was it formed? 1.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? 1.carbon-14 2.potassium-40 3.uranium rubidium A sample of rock contained 100 grams of potassium-40 ( 40 K) when it was formed. Today the rock contains 50 grams of potassium-40 ( 40 K). According to the Earth Science Reference Tables, what is an approximate age of the rock? 1.4 x 10 9 years 2.8 x 10 9 years 4.5 x 10 9 years 5.6 x 10 9 years

Radiocarbon Dating Radioactive carbon-14 (C 14 ), 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 (N 14 ), producing radioactive C 14. This C 14 is unstable and will eventually change back into N 14 through the process of radioactive decay. The proportions of C 14 and ordinary C 12 in Earth’s atmosphere remain approximately constant. Radioactive C 14, just like ordinary C 12, can combine with oxygen to make carbon dioxide. Plants use CO 2 during photosynthesis. The proportion of C 14 to C 12 in the cells and tissues of living plants is the same as the proportion of C 14 to C 12 in the atmosphere. After plants die, no new C 14 is taken in because there is no more photosynthesis. Meanwhile, the C 14 in the dead plant keeps changing back to N 14, so there is less and less C 14. The longer the plant has been dead, the less C 14 is found in the plant. The age of organic remains can be found by comparing how much C 14 is still in the organic remains to how much C 14 is in a living organism.

Radioactive C 14 was used to determine the geologic age of old wood preserved in a glacier. The amount of C 14 in the old wood is half the normal amount of C 14 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).

The End! Up next- our last topic: Fossils! Helpful Links: Help w/ pgs8-9 ESRT: and and Half-life animation: Half-life animation: How does Carbon dating work: How does Carbon dating work: Unconformity animations: Unconformity animations: and and