1. Ideas on the Origin of Life on Earth
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Ideas on the Origin of Life on Earth
General Biology
ANSWER KEY

2. Early Ideas
Spontaneous generation - the idea that nonliving material can produce life.
Examples:
mud producing fish
grain producing mice
decaying meat producing maggots

3. Redi’s Experiment Effort to disprove spontaneous generation
Decaying meat in uncovered control jars vs. covered experimental jars.
Results: maggots and flies filled the open jars but not covered jars. Showed only flies produce flies.

4. People still didn’t believe it…
Although Redi disproved spontaneous generation of large organisms, many scientists thought microorganisms must arise spontaneously, probably from a vital force in the air.

5. Pasteur’s Experiment (mid-1800s)

6. Two things must have occurred before life arose:
The formation of simple organic molecules
The organization of those molecules into more complex organic molecules such as proteins, carbohydrates, and nucleic acids.

7. Earth’s Early Atmosphere
Contained:
Little oxygen
Mostly water vapor, carbon dioxide gas, nitrogen gas, methane gas, ammonia gas
Energy sources - heat from Earth’s formation, lightning, UV radiation

9. Oparin’s Hypothesis
Energy from the sun, lightning, and earth’s heat triggered chemical reactions to produce small organic molecules from the substances in the atmosphere. Rain washed these into the oceans, forming a “primordial soup”.

10. Miller and Urey (1953)
Set up a simulation of conditions on early earth.
After 1 week, found they had produced several kinds of amino acids, sugars and other small organic molecules.
Supported Oparin’s hypothesis.

11. How did simple organic molecules form complex organic molecules?
Studies in 1950’s showed that if amino acids are heated without oxygen, they form proteins. A similar process produces ATP and nucleic acids from small molecules.
Therefore, this may have occurred on early earth in the warm pools of water.

12. How did these molecules become CELLS?
Sidney Fox: Protocells could be formed by heating solutions of amino acids.
Protocell is a large, ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division.

13. ~LIFE BEGAN!~
We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells.
Reminder:
prokaryotic:
example:
eukaryotic:
examples:

14. ~LIFE BEGAN!~
We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells.
Reminder:
prokaryotic: simple cell structure, no nucleus
example: bacteria
eukaryotic:complex cell structure, has nucleus
examples: protists, fungi, plants, animals

15. The First Cells
First cells were probably prokaryotes that evolved from protocells; didn’t need oxygen, used molecules in oceans for food.
At some point, some cells developed the ability to make their own food
CHEMOSYNTHESIS - making glucose from inorganic molecules, probably near deep sea vents or in hot springs. No light needed.

16. And later...
Some cells developed the ability use light to perform PHOTOSYNTHESIS. This started increasing the amount of oxygen in the atmosphere.
Some cells developed the ability to use oxygen through respiration.
Lightning caused some oxygen (O2) to form ozone (O3).
Protective layer, prevents most UV radiation from sun
stopped origin of cells; enabled evolution of more complex cells.

17. Evolution of Eukaryotic Cells
Lynn Margulis (1960s) - Endosymbiont Theory
Ancient bacteria may have “taken in” other bacteria, which evolved to become cell structures such as mitochondria and chloroplasts.
Supporting Evidence:
M & C have their own DNA (similar to prokaryotes)
M & C have ribosomes (similar to prokaryotes)
M & C reproduce independently within cells

18. And finally...
Over millions of years, these early cells evolved to the diversity of living things we have on Earth today!!
This likely involved many, many different mutations over time. Survival was likely determined through natural selection (“survival of the fittest”).

19. Evolutionary Timeline

20. Time From the Present First Records of:a
4.5 billion years ago
origin of the Earth b
* billion years ago
prokaryotic heterotrophs c
*2.5-3 billion years ago
prokaryotic autotrophs, first evidence of photosynthesis d
1.5 billion years ago
unicellular (single celled) eukaryotes e
650 million years ago
multicellular eukaryotes f
400 million years ago
plants invade the land g
300 million years ago
animals invade the land h
200 million years ago
first mammals i
150 million years ago
first dinosaurs j
100 million years ago
last dinosaurs k
*100,000 years ago
human development