1. ORIGIN OF LIFE SC.912.L.15.8 Describe the scientific explanations of the origin of life on Earth.
Essential Question: How does science help us explain how all life came to be?

2. Bell Ringer
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by the merging of prokaryotic organisms and their hosts. Which of the following is the best evidence to support the endosymbiotic theory?
A. Mitochondria and chloroplasts contain DNA similar to bacterial DNA.
B. Both prokaryotic and eukaryotic organisms require oxygen in order to use energy.
C. Bacteria, mitochondria, and chloroplasts all divide by mitosis, while the cells containing them divide by binary fission.
D. Bacteria and mitochondria contain many features that are similar to each other but different from those of chloroplasts.
Follow your classroom rituals and routines for bell ringers: 3 minutes
Have students put these in their notebooks on the left side
Pass out guided notes while students are completing this question.

3. Interactive Journal
Right side
Left side

4. What is the origin of life?
Even though scientifically the origin is uncertain, scientists do know that the earliest life form must have been:
Heterotrophic – cloudy atmosphere, too much radiation for photosynthesis or chemosynthesis
Anaerobes – live without oxygen in the atmosphere (Earth was acidic/plate disruptions)
Others?
Single-celled, prokaryotic, asexual binary fission
Which types of organisms developed first due to the early environmental conditions on Earth?
A. prokaryotic and aerobic
B. prokaryotic and anaerobic
C. eukaryotic and aerobic
D. eukaryotic and anaerobic
2009 What is Life - W.H. Freeman
And for life to rapidly evolve, oxygen was needed to first develop the ozone layer (UV filter) and then to gather in concentration in the troposphere for aerobic respiration
What developed to allow Oxygen to increase in concentration?

5. Louis Pasteur Contributions
Pasteur discovered the role of bacteria in fermentation.
His experiments with bacteria conclusively disproved the theory of spontaneous generation and led to the theory that infection is caused by germs.

6. Alexander Oparin Contributions
In 1924 he put forward a theory that life on Earth developed through gradual chemical evolution of carbon-based molecules in primordial soup
the mix of gases in the atmosphere and the energy from lightning strikes, amino acids could spontaneously form in the oceans

7. Lynn Margulis Contributions
Margulis is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted for how certain organelles were formed.
While her organelle genesis ideas are widely accepted, symbiotic relationships as a current method of introducing genetic variation is something of a fringe idea.

8. Evidence of Endosymbiosis theory
Chloroplast and Mitochondria
Double membranes
Outer membrane is of eukaryotic origin
Inner membrane is of prokaryotic origin
Single loop of DNA
Reproduce by binary fission
Have ribosomes of prokaryotic origin
About the same size as prokaryotes

9. The Miller Urey Experiment
In the 1950's, biochemists Stanley Miller and Harold Urey, conducted an experiment which demonstrated that several organic compounds could be formed spontaneously by simulating the conditions of Earth's early atmosphere. They designed an apparatus which held a mix of gases similar to those found in Earth's early atmosphere over a pool of water, representing Earth's early ocean. Electrodes delivered an electric current, simulating lightning, into the gas-filled chamber. However, there are still many skeptics of this theory who remain unconvinced.

10. Sidney Fox Contributions
The production of amino acids from inorganic molecules
1964 Dr. Sidney Fox based his experiments off of the information found in the Miller-Urey experiment.
The creation of proteinoids
He demonstrated that amino acids could spontaneously form small peptides. These amino acids and small peptides could be encouraged to form closed spherical membranes, which show many of the basic characteristics of 'life

11. Earth in 24 hours
Earth in 24 hours

12. Three scenarios have been proposed for the origin of life:
organic molecules :
were synthesized from inorganic compounds in the atmosphere
rained down on Earth from outer space;
were synthesized at hydrothermal vents on the ocean floor.
Chemical evolution
The formation of complex organic molecules from simpler inorganic molecules through chemical reactions in the oceans during the early history of the Earth; the first step in the development of life on this planet. The period of chemical evolution lasted less than a billion years.
Endosymbiotic theory
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Which takes a big part in the building blocks of life. This theory postulates that several key organelles of eukaryotes originated as symbioses between separate single-celled organisms. According to this theory, mitochondria, plastids and possibly other organelles--represent formerly free-living bacteria that were taken inside another cell as an endosymbiont.

13. We Do
Origins worksheet

14. Bell Ringer
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by the merging of prokaryotic organisms and their hosts. Which of the following is the best evidence to support the endosymbiotic theory?
A. Mitochondria and chloroplasts contain DNA similar to bacterial DNA.
B. Both prokaryotic and eukaryotic organisms require oxygen in order to use energy.
C. Bacteria, mitochondria, and chloroplasts all divide by mitosis, while the cells containing them divide by binary fission.
D. Bacteria and mitochondria contain many features that are similar to each other but different from those of chloroplasts.

15. Bell Ringer
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by the merging of prokaryotic organisms and their hosts. Which of the following is the best evidence to support the endosymbiotic theory?
A. Mitochondria and chloroplasts contain DNA similar to bacterial DNA.
B. Both prokaryotic and eukaryotic organisms require oxygen in order to use energy.
C. Bacteria, mitochondria, and chloroplasts all divide by mitosis, while the cells containing them divide by binary fission.
D. Bacteria and mitochondria contain many features that are similar to each other but different from those of chloroplasts.

16. You Do
According the the hypothesis of Oparin and the subsequent experiments of Miller and Urey, which of the following situations contributed to the origin of life on Earth?
A. Organic compounds formed from meteorites that had fallen to Earth.
B. Cells evolved in an environment lacking oxygen.
C. Organic compounds formed from gases available in the atmosphere.
D. Cells evolved from large prokaryotic cells that engulfed smaller prokaryotic cells
Correct answer C

17. Scientists theorize that it took a billion years or more for oxygen in the atmosphere to reach the levels of today. Based on this idea, the first cells could be classified as which of the following?
A. aerobic and photosynthetic
B. anaerobic and heterotrophic
C. photosynthetic and unicellular
D. heterotrophic and eukaryotic
Correct answer B

18. In the 1950s, Stanley Miller and Harold Urey conducted experiments in which they fired electrical sparks in the presence of a mixture of different gases. How did these experiments contribute to the theory of the origins of life on Earth?
A. They proved that organic molecules formed from the accumulation of debris from space.
B. They showed that organic molecules could be formed from materials available in the Earth's early atmosphere.
C. They determined that the age of organic molecules can be measured by the half-life of isotopes.
D. They discovered that organic molecules would not have formed without the presence of oxygen in the atmosphere.
Correct answer B