Lecture 11 - Chapter 25. The History of Life on Earth We...

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Chapter 25. The History of Life on Earth We will not cover section 25.5 in class. Macroevolution. The pattern of evolution over large time scales. Examples of macroevolutionary change include: The origin of photosynthesis First terrestrial vertebrates and plants Mass extinctions on the diversity of life
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Concept 25.1 Conditions of early Earth Earliest evidence of life comes from fossils of microorganims that are about 3.5 billion years old. The chemical and physical forces on early Earth coupled with the emerging force of natural selection could have produced very simple cells through a sequence of four main stages:
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Concept 25.1 Conditions of early Earth Stage 1. Synthesis of organic compounds on early Earth The solar system form about 4.6 billion years ago. Conditions favorable for the emergence of life started around 3.9 billion years ago. The first atmosphere had water vapor, compounds released from volcanic eruptions. As Earth cooled, the water vapor condensed into oceans.
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Concept 25.1 Conditions of early Earth In the 1920’s scientists Oparin and Haldane hypothesized that Earth’s early atmosphere was a reducing (electron-adding) environment in which organic compounds could have formed from simple molecules. The energy for this organic synthesis could have come from lighting and intense UV radiation. Haldane suggested that the early oceans were a solution of organic molecules, a “primitive soup” from which life arose.
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Concept 25.1 Conditions of early Earth In 1953 Miller and Urey tested the Oparin-Haldane hypothesis by creating laboratory conditions that emulated the primitive atmosphere of Earth. Their apparatus yielded a variety of amino acids and other organic compounds. However, it is unclear whether the atmosphere of young Earth contained enough methane and ammonia to be reducing. Growing evidence suggests that the early atmosphere
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LE 26-2 Water vapor CH 4 NH 3 H 2 Electrode Condenser Cold water Cooled water containing organic molecules Sample for chemical analysis H 2 O
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Concept 25.1 Conditions of early Earth Growing evidence suggests that the early atmosphere was made up primarily of nitrogen and carbon dioxide and was neither reducing or oxidizing. Experiments using a N 2 -CO 2 atmosphere have not produced organic compounds. The Miller-Urey experiments demonstrate that the abiotic synthesis of organic molecules is possible. Equal concentrations of D and L isomers of amino acids have been found in meteorites. Organisms use only L isomers.
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Concept 25.1 Conditions of early Earth Macromolecules could have assembled abiotically given the conditions on early Earth. Two key properties of life are accurate replication
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Lecture 11 - Chapter 25. The History of Life on Earth We...

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