Life History Chapter 12.3 don’t copy. IV. Geologic Time Scale A. Model of history of life on Earth...
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Transcript of Life History Chapter 12.3 don’t copy. IV. Geologic Time Scale A. Model of history of life on Earth...
![Page 1: Life History Chapter 12.3 don’t copy. IV. Geologic Time Scale A. Model of history of life on Earth 1. Most change happened slowly 2. Catastrophic events.](https://reader036.fdocuments.us/reader036/viewer/2022062321/56649f175503460f94c2d586/html5/thumbnails/1.jpg)
Life History
Chapter 12.3 don’t copy
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IV. Geologic Time Scale
A. Model of history of life on Earth1. Most change happened slowly2. Catastrophic events change surface + climate quickly
a. Put large amounts of fine dust in atmosphere
b. Volcanic eruptions, meteor impacts
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a. Period – smaller blocks based on fossils found in parts of each era
B. Divisions of Time
1. Era – big block determined by life form dominant at the time
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C. Precambrian era
1. Biggest time block in Earth’s history
2. From Earth’s formation 4.6 billion years ago 542 million years ago (mya)
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3. Earliest atmosphere – no O2
4. First cells – 3 bya anaerobic
a. cyanobacteria made O2 ozone layer
first eukaryotic cells
first life on land
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D. Paleozoic era
1. 542 to 251 mya2. Paleo- means ancient, -zoic means life3. Fossils of trilobites, snails, clams, and corals
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4. Fish, land plants, ferns, palms
5. Crawling and winged insects
15 foot flying cockroaches!!! Aren’t you glad they’re extinct?
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E. Mesozoic era
1. 251 to 65 mya
2. Mesozoic means middle life
3. Age of Reptiles, dinosaurs dominant
4. first birds
5. flowering plants
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6. End of era – giant meteor or asteroid mass extinction
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F. Cenozoic era
1. 65 mya still going on
2. Cenozoic means recent life
3. Cenozoic fossils closest to surface, easiest to find
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4. Age of Mammals, humans 4 mya, modern humans 40,000 ya
Ramses II
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G. Mass extinctions
1. Periods of time when many plants + animals went extinct
2. Most recent one between Meso- + Cenozoic 65 mya
Asteroids may have played a part in previous
mass extinctions.
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4. Biggest - Permian extinction (end of Paleo-) killed 90% of life
5. Allows new life forms to appear
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H. Absolute dating
1. Method of estimating age of fossil or rock in years
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a. Most elements are stable but some are not, they have too much energy
b. Radioactive decay – elements with too much energy release energy to get to their stable form
2. Radioactive decay
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Energy
Amount of the energetic form decreases and amount of the stable form of the element
increases
100 atomstoday
50 atomsafter 5 yrs
25 atomsafter 10 yrs
12 atomsafter 15 yrs
Energy
StableStable
Energy
Stable
Energy
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Radioactive Decay
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Number of Half-Lives
RadioactiveAtoms
1) Time it takes for half the energetic atoms to stabilize (decay)
c. Half Life
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2) happens at known rate
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1) uranium-238 to lead (half-life - 4.5 billion years)
d. Two elements
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2) C-14 (half-life - 5,730 years)a) in all living organisms, even us!
What is the second half-life of C-14 in total years?
5,730 x 2 = 11,460 years
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3. Using absolute dating
a. moon rocks thought to be same age as Earth
b. Scientists think Earth is 4.6 billion years old and life has existed for 3 billion
years on Earth