1. Biology, 9th ed,Sylvia Mader
Chapter 19
Chapter 19
Origin and History of Life
Origin and History of Life

2. Outline Origin of Life History of Life Factors Affecting Evolution
Primitive Earth
Origin of First Cells
History of Life
Fossils
The Precambrian
The Paleozoic
The Mesozoic
The Cenozoic
Factors Affecting Evolution
Continental Drift
Mass Extinctions

3. Origin of Life The earth & its atmosphere formed
The primordial seas formed
Complex molecules were synthesized
Polymers & self-replicating molecule are synthesized
Organic molecules were concentrated & isolated into protobionts
Primitive Heterotrophic prokaryotes formed
Primitive Autotrophic prokaryotes formed
O2 & ozone layer formed – abiotic evolution ends
Eukaryotes formed (endosymbiotic theory)

4. Enlightening Quote
Mark Twain, on science (undoubtedly evolutionary science), wrote:
“There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”

5. Another Enlightening Quote
Francis Crick said out of frustration,
“Every time I write a paper on the origin of life, I swear I will never write another one, because there is too much speculation running after too few facts”

6. Origin of the First Cell(s)

7. The Primitive Earth Primitive atmosphere: Most likely consisted of:
Water vapor
Nitrogen
Carbon dioxide
Small amounts of hydrogen and carbon monoxide
Little free oxygen
Originally too hot for liquid water to form
Earth cooled and water vapor condensed to liquid water

8. Monomers Evolve Stanley Miller (1953)
Conducted an experiment
Showed that biochemicals could be produced from simple nonbiological sources
Primitive atmospheric gases
Strong energy sources
Led to theory of the Hot Thin Soup

9. Miller’s & Urey’s Apparatus & Experiment.

10. Monomers Evolve 1) methane (CH4) 2) ammonia (NH3) 3) hydrogen (H2)
Aleksandr Oparin’s 1938 Hypothesis:
Suggested organic molecules could be formed in the presence of outside energy sources:
1) methane (CH4)
2) ammonia (NH3)
3) hydrogen (H2)
4) water (H2O)
Experiments performed by Stanley Miller and others show these gases in the primitive atmosphere reacted with one another to produce small organic molecules

11. Monomers Evolve These complex molecules included:
acetic acid
Formaldehyde
amino acids
These kinds of molecules would later serve as monomers, or building blocks, for the synthesis of polymers.
Lack of oxidation and decay allowed organic molecules to form a thick, warm organic soup

12. The Earth & Atmosphere
The primitive atmosphere contained little free oxygen (O2) and was a reducing atmosphere as opposed to the oxidizing atmosphere of today.
A reducing atmosphere lacks free O2 and allows formation of complex organic molecules.
An oxidizing atmosphere contains free O2 and inhibits formation of complex organic molecules.

13. Monomers Evolve
A.I Oparian and J.B.S. Haldane independently theorized that simple molecules were able to form only because oxygen was absent. As a very reactive molecule, oxygen had it been present, would have prevented the formation of organic molecules by supplanting most reactants in chemical reactions

14. Monomers Evolve
Stanley Miller tested the theories of Oparin and Haldane by simulating an experiment under primordial conditions. He applied electric sparks to simple gases (but no oxygen) connected to a flask of heated water. After one week, the water contained various organic molecules including amino acids.

15. Flaws in Miller-Urey Experiment
O2 present in primitive atmosphere
Kenneth Towe (Smithsonian Institute paleobiologist) reviewed the evidence in 1996 & concluded that “Early earth very likely had an atmosphere that contained free oxygen”
British geologists Harry Clemmey and Nick Badham wrote that the evidence showed “from the time of the earliest dated rocks at 3.7 billion years ago, Earth had an oxygenic atmosphere.”

16. Flaws in Miller-Urey Experiment
Primitive atmosphere not a reducing atmosphere.
1953 Miller-Urey (reducing atmosphere)
Methane, ammonia, hydrogen & water
1960’s Heinrich Holland, Princeton University geochemist & Philip Abelson, Carnegie Institute geophysicist – (neutral atmosphere)
Water vapor, carbon dioxide, nitrogen & hydrogen
Abelson concluded, “What is the evidence for a primitive methane-ammonia atmosphere on Earth? The answer is that there is no evidence for it, but much against it.”

17. Flaws in Miller-Urey Experiment
National Geographic March 1998 carries a photo of Stanley Miller next to his experimental apparatus. The caption reads:
“Approximating conditions on the early Earth in a 1952 experiment, Stanley Miller – now at UCSD – produced amino acids. ‘Once you get the equipment together it’s very simple’ he says”
Several pages later the article explains, “Many scientists now suspect that the early atmosphere was different from what Miller first supposed”
BUT A PICTURE IS WORTH 1,000 WORDS!!!

18. Origin of the First Cell(s)

19. Polymers Evolve
Monomers join to form polymers in the presence of enzymes
Protein-First Hypothesis:
Assumes protein enzymes arose first
DNA genes came afterwards
RNA-First Hypothesis:
Suggests only RNA was needed to progress toward formation of the first cell or cells

20. Quotes on the Origin of Life
The late astronomer Carl Sagan said,
“The receipt of a single message from space’ would be enough to know there’s an intelligence out there. That’s reasoning by analogy – we know that where there’s intelligent communication, there’s an intelligent cause.”
How do we deal with the vast amounts of information stored in the DNA molecule?

21. Protocell Evolves Protocells:
Hypothesized precursors to the first true cells
A structure with a lipid-protein membrane that carries on energy metabolism
Semipermeable-type boundary may form around coacervate droplets
Liposomes form spontaneously in liquid environments

22. Heterotrophophic Prokaryotes formed
If a protocell was a heterotrophic fermenter living on the organic molecules in the organic soup that was its environment; this suggests heterotrophs preceded autotrophs.
A heterotroph is an organism that cannot synthesize organic compounds from inorganic substances and therefore must take in preformed organic compounds. (ex. pathogenic bacteria)
An autotroph is an organism that makes organic molecules from inorganic nutrients. (ex. photosynthetic bacteria)

23. A Protocell Evolves
If the protocell evolved at hydrothermal vents, it would be chemosynthetic and autotrophs would have preceded heterotrophs.(ex. Chemosynthetic bacteria)
As there was no free O2, it is assumed that protocells carried on a form of fermentation.
First protocells had limited ability to break down organic molecules; it took millions of years for glycolysis to evolve.

24. Chemical Evolution at Hydrothermal Vents

25. Autotrophophic Prokaryotes formed
As a result of mutation, a heterotroph gained the ability to produce its own food
As an AUTOTROPH, this cell would be highly successful.

26. Oxygen & Ozone Layer formed
As a by-product of the photosynthetic activity of autotrophs, oxygen was released and accumulated in the atmosphere. The interaction of UV light and oxygen produced the ozone layer.
As a result of the formation of the ozone layer, incoming UV light was absorbed, preventing it from reaching the surface of the earth. Thus, the major source of energy for the abiotic synthesis of organic molecules and primitive cells was terminated.

27. Eukaryotes Formed Endosymbiotic Theory
Eukaryotic cells originated from a mutually beneficial association (symbiosis) among various kinds of prokaryotes.
Mitochondria, chloroplasts, and other organelles established residence inside another prokaryote, producing a eukaryote.

28. Endosymbiotic Theory Evidence for Endosymbiotic Theory
Mitochondria & Chloroplasts contain their own DNA.
Ribosomes of Mito & Chloro resemble those of bacteria.
Mito & Chloro reproduce independently (similar to binary fission)
Thylakoid membrane of chloroplasts similar to the membranes of photosynthetic cyanobacteria.

29. Quotes on the Origin of Life
Klaus Dose (Institute for Biochemistry in Mainz, Germany)
“More than thirty years of experimentation on the origin of life in the fields of chemical and molecular evolution have led to a better perception of the immensity of the problems of the origin of life on Earth rather than its solution. At present all discussions on principle theories and experiments in the field either end in stalemate or in a confession of ignorance”

30. Quotes on the Origin of Life
Robert Shapiro – chemistry professor New York University wrote in 1986:
“We have reached a situation where a theory has been accepted as fact by some, and possible contrary evidence is shunted aside.” He concluded that this is “mythology rather than science.”
Dean Kenyon – biologist SFSU, author of the book Biological Predestination. In 1984 he wrote in the forward to The Mysteries of Life’s Origin,
“The authors believe, and I now conclude, that there is a fundamental flaw in all current theories of the chemical origins of life.”

31. Quotes on the Origin of Life
Stanley Miller (40 years after his famous experiment) said in a great understatement to Scientific American,
“The problem of the origin of life has turned out to be much more difficult than I, and most other people, envisioned”