1. Early Origins
Chapter 19.1 & 19.3

2. How Did Life Begin? 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)

3. Early Earth
Early Scientists hypothesized that the Earth’s early atmosphere was rich in ammonia, methane, water vapor, and hydrogen.
Earth’s atmosphere lacked oxygen

4. How Did Life Begin? Step 1: Formation of the building blocks of life
Step 2: Formation of cells
Step 3: Formation of a reliable CODE for building proteins

5. Step 1: Formation of the Building Blocks of Life
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.

6. Step 1: Formation of the building blocks of life
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).

7. Step 1: Formation of the building blocks of life

8. Step 2: Formation of cells
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.

9. Step 3: Formation of a reliable CODE for building proteins
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.

10. Step 3: Formation of a reliable CODE for building proteins
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.

11. History of Life On Earth 19.3
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

12. Oldest Fossils
Stramatolites or mats of Cyanobacteria

13. History of Life On Earth
The earliest life forms on Earth were prokaryotic.(before the nucleus)
They were also almost certainly heterotrophs early on.  

14. Early History of Life Can Be Characterized By 3 Developments
Development #1: Autotrophy
Development #2: Evolution of Eukaryotic cells
Development #3: Evolution of Multicellular Organisms

15. Development #1: Autotrophy
Autotrophs make their own food by the process of photosynthesis.
The byproduct that autotrophs release into the atmosphere is oxygen.

16. Development #1: Autotrophy
Cyanobacteria were photosynthetic organisms that began adding oxygen to the atmosphere.

17. Development #1: Autotrophy
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

18. Development #2: Evolution of Eukaryotic Cells
The evolution of some eukaryotic organelles such as chloroplasts and mitochondria can be explained by the endosymbiotic theory.

19. Development #2: Evolution of Eukaryotic Cells
Endosymbiotic Theory:
Large Prokaryotic Cells engulfed Smaller aerobic bacteria and cyanobacteria, which then began to live inside the larger cells.
Aerobic bacteria are thought to give rise to the mitochondria.
Cyanobacteria (contain chlorophyll) are thought to give rise to chloroplasts.

21. Development #2: Evolution of Eukaryotic Cells
Evidence that supports the Endosymbiotic Theory:
Size & Structure: Mitochondria & Chloroplasts are the same size as most bacteria
Genetic Material: Mitochondria & Chloroplasts contain DNA different from the nucleus
Reproduction: Mitochondria and Chloroplasts reproduce similarly to bacteria (binary fission)

22. Development #3: Evolution of Multicellular Organisms
Only organisms made of eukaryotic cells can be multicellular
Multicellularity first developed in protists in Precambrian Time

23. The End