42. Briefly describe the formation of Earth.
A: It is proposed that the solar system was formed by a condensing nebula which is a cloud of gas and dust in space.  Over time, most of the material in the nebula pulled together due to gravity and materials that remained in the nebula's disk circled the newly formed sun.

Repeated collision of this space debris over time built up into planets of our solar system.  Many asteroids struck the planet Earth releasing enormous amount of heat which kept materials making up Earth in a molten state which eventually separated into different layers.

Hydrogen, carbon monoxide, and nitrogen were released from the interior which combined to form an atmosphere.  Oxygen only formed after the first forms of life had begun to evolve.  As impacts became less frequent, Earth cooled don, continents formed, and water vapor condensed as rain and got collected into large bodies of water.

43. What is the Miller-Urey experiment?
A: It suggests that organic compounds could be formed from inorganic materials by passing an electrical current, representing lightning, through a mixture of gases.

44. What are the two main early cell structure hypotheses?
A: - Iron-sulfide bubble hypothesis: when warm sodium sulfide is injected into cool iron-rich solution, they form a chimney-like structure.  These structures could have acted as the first cell membranes.

- Lipid membrane hypothesis: lipid membranes could form membrane-enclosed spheres or liposomes which could form around a variety of organic molecules.

45. List a few reasons that support the hypothesis that RNA, rather than DNA, was the genetic material that stored information in living things on early Earth.
A: - RNA can copy itself and chop itself into pieces without enzymes.

- Since RNA could fold into different shapes, it can perform more functions that DNA.

46. What is the theory of Endosymbiosis?
A: It is a relationship where one organism lives within the body of another and both benefit from the relationship.  The theory suggests that early mitochondria and chloroplasts were once simple prokaryotic cells that were taken up by larger prokaryotes.  The large cell got energy from mitochondria while the mitochondria found a stable environment and nutrients.

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