1. Theories of the Origin of Life
Chapter 19.3
SC.912.L.15.8
Describe the scientific explanations of the origin of life on Earth

2. Scientific Theory Vs. Scientific Law
Scientific theories and laws are very similar but different things.
Scientific Theory
Explains a natural phenomenon
Based on observations and data
99% proven, can change over time with new evidence
Scientific Law
States a natural phenomenon exist
Based on quantitative data
100% proven
Can never change

3. Theories on the Origin of Life
The origin of life is a big mystery that scientist have been trying to solve for years. There are many theories of where life began on Earth.
Aristotle
350 BCE
Spontaneous generation theory – life comes out of nowhere
Pasteur
1864
Biogenesis- life comes from other life
Arrhenius Panspermia
1903
Panspermia theory – life came from out of space in asteroids
Oparin Primordial Soup Theory
1924
Early life came from primitive molecules based on chemicals
Modern Theories
1950 – present
Chemical Evolution
RNA world

4. Early Earth’s Atmosphere
Earth’s early atmosphere contained little or no oxygen. It was principally composed of carbon dioxide, water vapor and nitrogen, with lesser amounts of carbon monoxide, hydrogen sulfide and hydrogen cyanide.

5. Early Atmosphere: Production of Oxygen
Microscopic fossils evidence shows that prokaryotes resembling bacteria have been found in Archean rocks dating 3.5 billion years old. These evolved in the absence of oxygen Fossil evidence also shows that photosynthetic bacteria began producing oxygen about 2.2 billion years ago. The increase of oxygen reduced the prokaryotes bacteria and organisms that evolved new metabolic ways to use oxygen for respiration increased.

6. Organic Molecules: Primordial Soup Theory
The primordial soup theory was hypothesis by various scientist that build on each others work. Alexander Oparin in 1922s had believed that organic molecules had developed from the gases of Earth’s early atmosphere. However he wasn’t able to perform experiments. Miller and Urey in the 1950’s conducted a series of experiments on the same hypothesis.

7. Organic Molecules: Primordial Soup Theory – Miller and Urey
In 1953 chemist Stanley Miller and Harold Urey tried to answer the question: “Could organic molecules assemble under conditions on early Earth’s atmosphere?”
Experiment:
Used a flask of water to simulate ocean, boiled it and added methane, ammonia and hydrogen to simulate early Earth’s atmosphere.
The passed the gases through electricity to simulate lightning.
Then passed them through condensed chamber, to create rain drops (water cycle)
Circulated the experiment in the apparatus for a week.
Results
Brown water that contained 21 amino acids, building blocks of proteins.

8. Organic Molecules: Primordial Soup Theory
Miller and Urey’s experiment suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds on a primitive Earth. However: Miller and Urey’s ideas of early Earth’s atmosphere were incorrect. New experiments based on current ideas of the early atmosphere have also produced organic compounds, in 1995 Miller’s more accurate mixture produced cytosine and uracil, 2 bases found in RNA.

9. Organic Molecules: Endosymbiosis -Margulis
Endosymbiotic theory by scientist Lynn Margulis hypothesis that about 2 billion years ago some ancient prokaryotes began evolving internal cell membranes. Remember that there are two types of cell known as of today:
Prokaryotic Cells
Bacteria
No nucleus
No other membrane-bound organelle
Eukaryotic Cells
Single celled or multi cell organism
Animals, plants, fungi
Organelles
nucleus

10. Organic Molecules: Endosymbiotic Theory - Margulis
These prokaryotes were the ancestors of eukaryotic organisms today. According to Endosymbiotic theory prokaryotic cells entered those ancestral eukaryotic cells. They did not infect their host, as parasites, host cell didn’t digest them, instead the prokaryotic cell began living inside the eukaryotic cell. Endosymbiotic theory proposes that symbiotic relationships evolved over time, between primitive eukaryotic cells and the prokaryotic cells within them.

11. Organic Molecules: Endosymbiotic Theory - Margulis
This was proposed based on the data observed by scientist a century ago. They observed that mitochondria and chloroplast resembled the cell membrane of free living prokaryotic cells. This led to the hypothesis and theory. Margulis found data that could support this theory in 1960.

12. Chemical Evolution
The idea that earliest organisms on Earth evolved from simple compounds to more complex through a series of events using chemicals and some form of spark.
Various theories are included under chemical evolution:
Miller and Urey’s theory – early atmosphere with a spark
Deep Sea vent Theory – deep ocean chemosynthesis
Spark theory – a spark with chemicals

13. Chemical Evolution Theory
Early Earth’s atmosphere was radically different – nitrogen, carbon dioxide, water vapor
Reducing, not oxidizing atmosphere like today.
A series of chemical reactions spark first life
Energy such as solar radiation drove these reactions
Organic molecules evolved from simple to complex

14. Scientific Theory
The theories on the Origin of Life are all scientifically accepted theories that are based on observational data and evidence that supports those theories to an extend, however they do not prove 100% the origin of life and therefore are only accepted scientifically theories. They explain a possible origin but do not prove it completely. A scientific law would not explain the origin of life but state it as a fact based on 100% prove. The scientific body of knowledge is based on work, research, data and ideas from past scientist that continues to build forward.