chapter 19 origin and history of...
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Origin and History of Life
Chapter 19
Origin and History of Life
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OutlineOrigin of Life
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
Origin and History of Life
4Enlightening 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.”
Origin and History of Life
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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”
Origin and History of LifeWhat is Life?
organized as cells
respond to stimuli
regulate internal processes (aka homeostasis)
• use energy to grow
- metabolism
develop
reproduce
- heredity
DNA / RNA
- adaptation & evolution
Origin and History of Life
The Origin of Life is Hypothesis
Special Creation
Was life created by a supernatural or divine force?
not testable
Extraterrestrial Origin
Was the original source of organic (carbon) materials comets & meteorites striking early Earth?
testable
Spontaneous Abiotic Origin
Did life evolve spontaneously from inorganic molecules?
testable
Origin and History of Life
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Origin of
the First
Cell(s)
Origin and History of Life
When did life form?
Age of the Earth: 4.6 billion years
Oldest rocks: 3.8 – 4.0 billion years
Oceans established > 3.8 billion years ago
Life not possible during period of heavy bombardment ~ 4.0 billion years ago
Signatures of life: 12C/13C suggests photosynthetic life existed ~ 4.0 billion years ago
Origin and History of Life
Earliest life on Earth
Stromatolites ~ 3.8 billion years old
Earliest known fossils ~ 3.5 billion
years old
Origin and History of Life
Where did life form?
Rule out lands of the Earth
Oceans, lakes, ponds, tide pools?
Deep ocean geothermal vents?
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The Primitive EarthPrimitive atmosphere:
Most likely consisted of:
- Water vapor
- Nitrogen
- Carbon dioxide
- Small amounts of hydrogen and carbon monoxide
Little free oxygen (anaerobic respiration)
Originally too hot for liquid water to form
Earth cooled and water vapor condensed to liquid water
Origin and History of LifeStanley Miller
University of Chicago
produced-amino acids
-hydrocarbons-nitrogen bases-other organics
It’s ALIVE!
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Monomers EvolveStanley 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
Origin and History of Life
Miller Urey Experiment
Water vapor + methane + H2 + (CH4) + ammonia (NH3)
Primitive ocean
Source of energy
Condensation and recycle
Ran for a week
Condensed mixture contained amino acids and complex organic molecules
Origin and History of Life
Problem – early atmosphere was mostly CO2, little methane and ammonia
Experiment redone with CO2 and UV light
Less quantities but produced all amino acids found in life on Earth
Complex sugars and lipids formed
All 5 chemical bases used in DNA and RNA formed
Miller Urey Experiment
17Miller’s & Urey’sApparatus & Experiment.
Notice no O2
Origin and History of Life
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Monomers EvolveAleksandr 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
Origin and History of Life
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Monomers EvolveThese 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
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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 O2and allows formation of complex organic molecules.
An oxidizing atmosphere contains free O2 and inhibits formation of complex organic molecules.
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Monomers Evolve
A.I Oparian and J.B.S. Haldaneindependently 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
Origin and History of Life
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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.
Origin and History of Life
23Flaws 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.”
Origin and History of Life
24Flaws 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.”
Origin and History of Life
25Flaws 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!!!
Origin and History of Life
Other sources of Organic Molecules
External sources (comets, asteroids, meteors)
100’s of tons of debris fall to Earth each year
Murchison Meteorite (1969)
74 amino acids – 8 used by life on earth, 55 extraterrestrial found
All 5 bases used in DNA/RNA found
Simple sugars and fatty acids were found
Origin and History of Life
Organic Molecules in Comets
Origin and History of Life
Problems still to overcome
Miller – Urey type experiments do not produce all of the ingredients for DNA and RNA
Earth’s primitive atmosphere still debatable (though the absence of free oxygen is a must!)
Sources of energy are varied
However, definite pathways to life are evident in each experiment
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Origin of the First
Cell(s)
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Polymers EvolveMonomers 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
-DNA genes came afterwards
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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?
Quotes on the Origin of Life
Origin and History of Life
Key Events in Origin of Life
Key events in evolutionary history of life on Earth
life originated 3.5–4.0 bya
Origin and History of Life
Origin of Genetics
RNA is likely first genetic material
multi-functional
codes information
- self-replicating molecule
- makes inheritance possible
- natural selection & evolution
enzyme functions
- ribozymes
- replication
regulatory molecule
transport molecule
- tRNA & mRNA
Dawn of natural selection
Origin and History of Life
Prokaryotes
Prokaryotes dominated life on Earth from 3.5–2.0 bya
3.5 billion year old fossil of bacteria modern bacteria
chains of one-celledcyanobacteria
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Origin of Cells (Protocells)
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
Origin and History of Life
36Heterotrophophic
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)
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A Protocell EvolvesIf 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.
38Chemical Evolutionat Hydrothermal Vents