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).


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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.


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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.


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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.


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Cyanobacteria were photosynthetic organisms that began adding oxygen to the atmosphere.


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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


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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.


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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)


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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

early origins

Documents

formation of cells step

building blocks of life

building proteins

cells form

oxygen early earth

reliable code

earliest code

offspring cells