Early Origins
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Transcript of Early Origins
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Early OriginsChapter 19.1 & 19.3
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The ideas presented here are hypotheses.
The evidence for life’s origin’s are speculative and difficult to find (since these events occurred much further back in Earth’s history)
How Did Life Begin?
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Early Scientists hypothesized that the Earth’s early atmosphere was rich in ammonia, methane, water vapor, and hydrogen.
Earth’s atmosphere lacked oxygen
Early Earth
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Step 1: Formation of the building blocks of life
Step 2: Formation of cells
Step 3: Formation of a reliable CODE for building proteins
How Did Life Begin?
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Can the components of living organisms form all by themselves from simple chemicals? YES
The Miller-Urey experiment demonstrated how cells formed all by themselves.
Step 1: Formation of the Building Blocks of Life
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Miller-Urey Experiment:
Miller and Urey placed Ammonia, Water, Methane, and Hydrogen gases into a device.
To simulate lightening they used electrical sparks. Heat could also be used
They found organic molecules in the device after 3 days. (fats/lipids & amino acids).
Step 1: Formation of the building blocks of life
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Step 1: Formation of the building blocks of life
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The Miller-Urey experiment did NOT yield living organisms … so how did the first cells form?
Experiments show that membranes can form by themselves when lipids (fats) are added to water.
Step 2: Formation of cells
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Cells may have formed on their own, but eventually cells would need to replicate and pass on their ability to make proteins to offspring cells.
Some evidence exists that the earliest code for building proteins may have been an RNA code.
Step 3: Formation of a reliable CODE for building proteins
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RNA can code for building proteins as well as serving as enzymes to speed up other reactions.
Later, a DNA code developed which was more stable and held the protein code longer.
Step 3: Formation of a reliable CODE for building proteins
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Earth is 4.6 billion years old
Fossil evidence indicates that the earliest life on Earth might have existed 3.5 billion years ago…………
Suggesting that it took approximately 1.1 billion years for life to evolve
History of Life On Earth 19.3
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Stramatolites or mats of Cyanobacteria
Oldest Fossils
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The earliest life forms on Earth were prokaryotic.(before the nucleus)
They were also almost certainly heterotrophs early on.
History of Life On Earth
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Development #1: Autotrophy
Development #2: Evolution of Eukaryotic cells
Development #3: Evolution of Multicellular Organisms
Early History of Life Can Be Characterized By 3 Developments
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Autotrophs make their own food by the process of photosynthesis.
The byproduct that autotrophs release into the atmosphere is oxygen.
Development #1: Autotrophy
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Cyanobacteria were photosynthetic organisms that began adding oxygen to the atmosphere.
Development #1: Autotrophy
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Over time oxygen built up in the atmosphere, eventually forming the Ozone Layer O3
The Ozone Layer blocked UV rays to allow for land life
Development #1: Autotrophy
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The evolution of some eukaryotic organelles such as chloroplasts and mitochondria can be explained by the endosymbiotic theory.
Development #2: Evolution of Eukaryotic Cells
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Endosymbiotic Theory:
1. Large Prokaryotic Cells engulfed Smaller aerobic bacteria and cyanobacteria, which then began to live inside the larger cells.
2. Aerobic bacteria are thought to give rise to the mitochondria.
3. Cyanobacteria (contain chlorophyll) are thought to give rise to chloroplasts.
Development #2: Evolution of Eukaryotic Cells
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Evidence that supports the Endosymbiotic Theory:
1. Size & Structure: Mitochondria & Chloroplasts are the same size as most bacteria
2. Genetic Material: Mitochondria & Chloroplasts contain DNA different from the nucleus
3. Reproduction: Mitochondria and Chloroplasts reproduce similarly to bacteria (binary fission)
Development #2: Evolution of Eukaryotic Cells
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Only organisms made of eukaryotic cells can be multicellular
Multicellularity first developed in protists in Precambrian Time
Development #3: Evolution of Multicellular Organisms
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The End