1. Unit 1 NOS/Evolution ppt #6 Evolution: Early Earth History
Photo credit: Jackie Beckett/American Museum of Natural History
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2. Earth is about 4.6 Billion years old!!
Fossil records tell the Earth’s story. Over years many many layers of rock have formed. Many fossils are found within layers of rock. Fossils are the preserved remains or traces of organisms that lived in the past
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3. Interpreting Fossil Evidence
Interpreting fossil evidence to show evolution or organisms
Relative Dating
Using the LAW of SUPERPOSITION:
Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.
In relative dating, the age of a fossil is determined by comparing its placement to that of fossils in other layers of rock.
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4. Interpreting Fossil Evidence
Relative Dating
In relative dating, a paleontologist estimates a fossil’s age in comparison with that of other fossils. Each of these fossils is an index fossil. It enables scientists to date the rock layer in which it is found. Scientists can also use index fossils to date rocks from different locations.
Photo credit: l. ©David Hanson/Stone; r. ©CORBIS
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In Relative dating you are comparing 1 fossil to another, generating a history. For this you need an INDEX FOSSIL
INDEX FOSSIL = An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range.
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6. Interpreting Fossil Evidence
Interpreting Fossil Evidence to show evolution of organisms
2. Absolute Dating= radioactive dating
Paleontologists determine the age of fossils using the fact that elements decay into measureable radioactive quantities. Scientists use radioactive decay to assign an absolute age to rocks
Using radioactive decay, C12-C14scientists can determine true age of a fossil.
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7. Radioactive dating is the use of half-lives to determine the age of a sample.
A half-life is the length of time required for half of the radioactive atoms in a sample to decay.

8. Interpreting Fossil Evidence
By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived.
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.
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9. Compare/Contrast Table
Section 17-1
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to another rock or fossil (that is, older or younger)
Age of a fossil in years
Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock
Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen
Imprecision and limitations of age data
Difficulty of radioassay laboratory methods

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Geologic Time Scale
Paleontologists use a scale called the geologic time scale to represent evolutionary time.
It is time on the scale of the history of Earth, which spans 4.6 billion years
Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide.
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11. Geological time scale shows macroevolution marked by mass extinctions and episodic speciation. Episodic speciation is a pattern of periodic large scale increase in new species that follows mass extinctions.

12. Compare/Contrast Table
Section 17-1

13. Over Earth’s History, 99.9% of all species that have lived on Earth have become extinct, which means that the species has died out.
Extinction means the death of an entire species.

14. Major Extinctions Precambrian Extinction:
The abrupt and nearly complete disappearance of life form in late Precambrian may have resulted from unbalanced predation, grazing, or competition, or yet another environmental crisis such as supercontinent breakup, changes in ocean chemistry, and/or rising sea levels.
Whatever the causes, most species disappeared by the end of the Precambrian, about 542 million years ago.
Their extinction, however, appears to have paved the way for a spectacular evolution of much more familiar life, which marks the beginning of the modern Phanerozoic Eon: the Cambrian explosion.

15. Cambrian Explosion
Cambrian explosion followed Precambrian extinction. The evidence shows that nearly all modern animal phyla, including our own chordate phylum, are represented in this diversity of life.

16. Major Extinctions Permian Extinction:
During the Permian period, all the major landmasses of earth combined into a single supercontinent, Pangaea. During the formation of the supercontinent Pangaea, most marine invertebrate species disappeared with the loss of their coastal habitats. The Permian ended with the most massive extinction of all time; 99.5% of all species disappeared, opening the door for a new radiation of species in the Mesozoic.

17. Major Extinctions “K-T” (Cretaceous-Tertiary) Extinction:
The dramatic extinction of all dinosaurs (except the lineage which led to birds) marked the end of the Cretaceous. A collision/explosion between the Earth and a comet or asteroid could have spread debris which
set off tsunamis, altered the climate (including acid rain), and reduced sunlight 10-20%. A climatic shift to cooler temperatures because of diminished solar energy coincided with the extinction of dinosaurs.
A consequent reduction in photosynthesis would have caused a drastic disruption in food chains. The massive extinction and sharp geologic line led geologists to define the end of the Mesozoic and the beginning of our modern Era, the Cenozoic, with this event.

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Formation of Earth
Evolution of THE FIRST ORGANISMS…
What substances made up Earth's early atmosphere?
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Formation of Earth
Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
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21. The Puzzle of Life's Origin
Evidence suggests that 200–300 million years after Earth had liquid water, cells similar to modern bacteria were common.
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22. The Puzzle of Life's Origin
Formation of Protocells 
In certain conditions, large organic molecules like RNA form tiny bubbles called protocells.
Protocells are not cells, but they have selectively permeable membranes and can store and release energy.
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23. The Puzzle of Life's Origin
Hypotheses suggest that structures similar to protocells might have acquired more characteristics of living cells.
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24. The Puzzle of Life's Origin
Evolution of RNA and DNA 
How could DNA and RNA have evolved? Several hypotheses suggest:
Some RNA sequences can help DNA replicate under the right conditions.
Some RNA molecules can even grow and duplicate themselves suggesting RNA might have existed before DNA.
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Free Oxygen
About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans.
Next, oxygen gas accumulated in the atmosphere.
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Free Oxygen
The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.
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27. Origin of Eukaryotic Cells
The Endosymbiotic Theory
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.
Prokaryotes became the organelles within the Eukaryotic cell.
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28. Origin of Eukaryotic Cells
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Plants and plantlike protists
Aerobic
bacteria
Photosynthetic bacteria
Nuclear envelope
evolving
Mitochondrion
Primitive Photosynthetic
Eukaryote
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Animals, fungi, and
non-plantlike protists
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
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29. Origin of Eukaryotic Cells
About 2 billion years ago, prokaryotic cells began evolving internal cell membranes.
The result was the ancestor of all eukaryotic cells.
According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotes.
Eukaryotic, multicellular life evolved with sexual reproduction which increases genetic variability. Thus…evolution of higher life forms!
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30. Concept Map Evolution of first life Section 17-2
Early Earth was hot; atmosphere contained poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the oceans..
Small sequences of RNA may have formed and replicated.
First prokaryotes formed when RNA or DNA was enclosed in microspheres.
Later prokaryotes were photosynthetic and produced oxygen.
An oxygenated atmosphere capped by the ozone layer protected Earth.
First eukaryotes may have been communities of prokaryotes.
Multicellular eukaryotes evolved.
Sexual reproduction increased genetic variability, hastening evolution.