1. Earth’s Early History Essential Questions:
How did life on Earth evolve?
What were the conditions on Earth like when life evolved?

2. Early Ideas: Spontaneous Generation
About 2300 years ago, Aristotle
argued that air provided a vital life force
That could produce life from nonliving
substances. This is called spontaneous generation.
The idea of spontaneous generation prevailed for thousands of years.
This idea was not formally tested until the 1700s.

3. How did we go from Spontaneous Generation to Biogenesis??
Life from air
Life from life

4. Early Earth
The atmosphere was very different than it is now, containing little or no oxygen.
Earth was too hot for liquid water.
Once the surface cooled enough for rocks to form, the surface was covered with volcanic activity.

5. Early Earth
About 3.8 billion years ago the Earth cooled enough for liquid water to remain.
Thunderstorms drenched the planet and oceans covered most of the surface.
Carbon, Hydrogen, Nitrogen, and Oxygen have existed on Earth since its formation.

6. Early Earth
If early earth was so harsh,
how did life come about?!

7. Key Scientists – Origin of Life
Francesco Redi ( )
First strike against spontaneous generation, his work:
Remember, around 1678, Anton van Leeuwenhoek observed “animalcules” in water. We now know that these are protozoa.
Experimental Group: Covered jars with meat = NO maggots
Control Group: Meat in uncovered jars = maggots
Conclusion: Only flies where there are
maggots AND only maggots where there had been flies… flies must come from flies.
It was concluded and believed they were a product of spontaneous generation from a “vital force” or life force in the air.
*As the microscope became a widely used tool for scientists, microorganisms were seen everywhere.

8. Key Scientists – Origin of Life Key Scientists – Origin of Life
Lazzaro Spallanzani ( )
Experimental Group: Boiled meat broth and sealed it in flasks = no microorganisms
Control Group: Boiled meat broth, unsealed flask=microorganisms.
Conclusion: Only had presence of microorganisms when they had access to the broth.
*His doubters claimed he had killed the “vital force” in the air when he boiled the broth and it could then not generate life.
It was convincing enough to keep the belief of spontaneous generation going for another 100 years!

9. Key Scientists – Origin of Life
Louis Pasteur ( )
Experiment: Boiled broth and enclosed it in an “S” curved neck flask. It was open and exposed to air, however not directly. Exposed for 1 year, no microorganisms; Removed “S” curve and exposed it for 1 day! = microorganisms
Conclusion: Spontaneous generation was disproved and biogenesis theory was substantiated. (Confirmed, make real or actuated) Contamination came from other microorganisms, not “air”.
Modern biologists support biogenesis, the idea that “living organisms only come from other living organisms.”
That then brings up the question of how life began on Planet Earth.
If Life can only come from life, we know at some point there had to be a start to “life”…
Where would you start looking for early life?

10. Key Scientists – Origin of Life
Oparin’s Ideas:
Alexander Oparin ( )
NO EXPERIMENTS!!
Earth’s early atmosphere: HCN, CO2, CO, N, H, S, HOH
Stated that the earliest living organisms on earth were simple heterotrophs (organisms that cannot make their own food)
Knew these elements (in the form of various gases) were present in the earth’s early atmosphere.
When heated (geologic activity) they might form organic compounds.
Once condensed these compounds would be in earth’s water bodies.
Oparin: “Life arose from the oceans.”
He believed that energy from lightning and the sun can spark chemical reactions to create macromolecules like proteins.
Heterotrophs ate the organic molecules in their environment until the food sources were very scarce
Organisms needed another source of energy
Autotrophs evolved (organisms that can make their own food source)
Oxygen became prevalent in environment so cellular respiration was possible
Eukaryotes evolved

11. Key Scientists – Origin of Life
Alexander Oparin ( )

12. Key Scientists – Origin of Life
In the 1950’s Stanley Miller and Harold Urey designed an experiment to simulate the conditions of early Earth.

13. Key Scientists – Origin of Life
In the 1950’s Stanley Miller and Harold Urey designed an experiment to simulate the conditions of early Earth.
They used Oparin’s concept and designed a contained experiment.
They passed sparks (representing lightning) through a mixture of hydrogen, methane, ammonia, and water (representing the atmosphere)

14. Miller and Urey showed that the mixtures of organic compounds necessary for life could have arisen on primitive earth!
Miller continued to perform experiments like the one in the 1950s. In 1995, he was able to produce cytosine and uracil, two of the bases found in RNA, a nucleic acid.

15. Key Scientists – Origin of Life
Sidney Fox ( )
-Studied the development of the first cells; found structures that have some cell life characteristics.
Microspheres – microscopic droplet enclosed by a membrane of organic molecules. (Predominantly proteins.)
They can form buds, split and take up certain substances from surroundings.
Microspheres
Sydney Fox produced coacervates by heating solutions of amino acids.
Coacervates – small organic droplet formed by different types of organic molecules.
They can grow and take up substances from surroundings. (lipid bi-layer)
NOTE: These are NOT ALIVE  no heredity, instead of reproduction, they form spontaneously under proper conditions.
Coacervates

16. Coacervates  Protocells
Scientists hypothesize that coacervates acquired more and more characteristics of living cells as time went on, eventually becoming early forms of bacteria.

17. Protocells Protocells are actually theoretical!
They are extremely simplified versions of cells.
They act alive but aren’t!