10_LifeInSolarSys - GEL36 SOLAR SYSTEM Lecture 10 Life in...

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1 GEL36 SOLAR SYSTEM Lecture 10: “Life in the Solar System and Beyond?” (Ch. 26) Goal of the Lecture: To investigate the origin of life on Earth, the possibility of life in our solar system, and the potential for life elsewhere in the universe. The idea is to gain a deeper appreciation of the special and unique planet that is Earth. Origin of Life . . . All theories about the origin of life based on the rules of chemistry, planetary physics, and informed speculation about the state of the early earth. . . . . Numerous competing theories for the various steps and the fact of the matter is that no one actually knows. No direct physical or astronomical evidence exists. Fundamental requirements for life to originate and evolve: 1) simple inorganic and organic molecules – supplied by impacts with asteroids and comets during planetary accretion and released to the planet’s surface through outgassing volcanoes - four elements that combine to form organic molecules: C, H, N, O - simple organic compounds like amino acids & sugars are found in carbonaceous chondrites (see below) and in comet dust - Carbon is particularly suitable as a building block for life because it is abundant in the universe (4 th most common element), and no other known element can naturally form the complex, stable molecular chains necessary for life as we know it. 2) liquid water to aid in the synthesis of complex organic molecules from simple compounds - likely brought to Earth and all other planetary bodies by comets, then ‘outgassed’ through magma oceans or volcanoes - liquid water aids chemical reactions - liquid water acts as a medium for reactions and transportation - liquid water changes temperature easily Earth lies in the “habitable zone” (aka “Goldilocks zone”) around the sun where the pressures and temperatures are “just right” for water to occur in a liquid form on its surface.
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2 - most other planets or moons in the solar system are either too hot or too cold for liquid water to exist on the surface (but some have the potential for water below the surface). - Venus and Mercury are too close to the sun – water would vaporize. - planets beyond about Mars are too far away – water would freeze - some planets and moons are too small to retain an appreciable atmosphere or hydrosphere (Moon, Mercury and Mars all have low escape velocities). - habitable zones where water takes the form of a liquid also occur on certain moons of the Jovian planets where the tidal energy of their huge mother planets creates internal heat inside the moons 3) Energy is needed to "move" the chemical reactions to transform non-living organic molecules to ‘life’ - heat from volcanic lava - ultraviolet radiation from the sun - electrical energy from lightning - heat from meteorite impacts 4) Construction of complex organic molecules (e.g., proteins, nucleic acids, carbohydrates) followed by replication and development of miniscule proto-organisms * Inorganic elements to simple organic molecules (easy) – complex organic molecules to
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10_LifeInSolarSys - GEL36 SOLAR SYSTEM Lecture 10 Life in...

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