AST251 Midterm Notes

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Department
Astronomy & Astrophysics
Course
AST251H1
Professor
H.Pfeiffer
Semester
Winter

Description
AST251 Midterm NotesLecture 1How did life begin and evolve on Earth How did the Earth formCan life exist elsewhere in the Universe WhereWhat is lifeoWe can recognize life but how do we knowoWe have NO good definition of lifecan describe it but cant define it oDarwinian genetic definitiona system capable of evolution by natural selection Has drawbacksmain time needed to detect any evolutionTo search for life in the universe then we will look for what we knowoBacteria and microbesoPlants oAnimalsoIntelligent lifeThe only life we know of right now is the life on Earth no manifestations of life currently known anywhere else Where to lookoSolar systemcomplex life seems to exist only on Earth but other planets and moons may contain microbial lifeoExtrasolar planets in the habitable zones around starsWhen a planet is deemed habitable is life guaranteedHow difficult is it for life to originate even in acceptable conditions Three essential groups of sciencesoAstronomy and astrophysicsAddresses the questions How was the Earth formed Are there other celestial bodies that may harbor lifeoEarth sciencesHow does the Earth function the only known planet with life oBiologyHow did the life as we know originate How does it functionThree lines of evidence that indicate that biological life is common in the UniverseoOrganic molecules are common oLife originated quicklyperhaps as early as 39 Gyr ago only 06 Gyr afterformation of EarthoVery high degree of lifes adaptability in spite of changing Earth conditionsLong time periods6oMyrmillion yr1 000 000 yr10 yr9oGyrbillion yr1 000 000 000 yr10 yrSpeculation on extraterrestrial lifeoSolid flat earth with some mysterious phenomena in the skyoPredictions of astronomical phenomena eg eclipses by the Babylonians and the Mayans 2500 BCEtheir purely empirical models sometimes worked but without understandingoEarly conclusionhumans plants and animals the only types of lifeoGreek philosophers 2500 BCEDemocritus 460370 BCEatoms are indivisible units that make up the four main elements earth air fire water would have inevitably led to belief in extraterrestrial life since it is natural to assume that the same processes that created this world couldve created othersAristotle 350 BCEfour elements confined to Earth while the Heavens consist of ether the fifth elementthe world must be unique there cannot be several worldsEpicurus 341270 BCEatomist There are different worlds both like and unlike this world of ours we must believe that in all worlds there are living creatures and plants and other things we see in this worldMetrodorus of Chios 400 BCEatomist student of Epicurus It is unnatural in a large field to only have one shaft of wheat and in the infinite universe only one living worldTitus Lucretius Carus 50 BCENothing in the universe is unique and alone and therefore in other regions there must be other Earths inhabited by different tribes of men and breeds of beaststho1112 c Aristotles doctrine that the Earth and Man are special is incorporated into the Western and Christian thoughtThomas Aquinas integrated Aristotles philosophy into Christian theology saying that God could create many worlds but obviously created just oneQuestioning the one Earthbased Cosmos was one of 217 reasons for excommunicationo15001700 Copernicus model of the Solar System 1543 slowly accepted after discoveries of Brache Kepler Newtonas opposed to the Ptolemy geocentric model5 visible planets and the Earth revolve around Sun heliocentric and the moon is a satellite of the EarthEarth no longer center of universeCopernican principle the principle of mediocrity Essence of principleEarth is not specialBrahe et al observed carefully whats going on then developed simple rules to explain universe
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