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ENVR 202 - Lec 3.docx

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McGill University
ENVR 202
Brian Leung

Lecture 3 - (January 14 , 2013) CHNOPS – most abundant elements, carbon based life, why?  Chance, history, necessity (something that is predictable, that will follow as a result of physical laws) Reading:  “evolving Earth” ch 10, pages 1-9 – origin of solar sys, Earht, atmosphere and the moon Formation of the Solar Sys and Earth  Hard – Earth is our only example  Was it a lucky accident (statistical exception)? Or a predictable event (highly probable)?  How do we reconstruct the steps leading to an event that happened only once? o Worth thinking about, how do we approach this concept  How long ago was Earth born? How was it different in the past? Story of a Solar System  Begins with death of a previous one (star) o We can see these “star deaths” o A star becomes a nova or supernova, destroying itself and it‟s solar sys  At the same time as it dies, elements are made and the seeds of a new solar sys are created o All elements of periodic table built during that high energy reaction  Something like this happened ~5 billion yrs ago  A Model for which we have observations of some the stages that we have connected to a series of processes, made sense of certain obvs, connected them in a sequence based on processes which then develop a predictable pattern based on stages  A Model o What evidence supports it? o Does it predict patterns? o What patterns disprove it? Hardest Q to answer  Remnants of a destroyed solar sys are visible o Nebula – diffused clouds of gases and dust o Ex: Crab Nebula in constellation Taurus  Ring like pattern w/in the cloud of gas and dust  RINGS: matter moved through space due to shock waves. Shockwave compresses cloud o Nebula (dense cloud) left behind after passage of shockwave  Collection of denser clouds, no longer dispersed  Building blocks of future solar sys  Nebula -> solar sys o Predictable phys processes o Gravitational energy is converted to heat o Vaporization of all elements occurs o Most heat at center – 10*10^6 K , nuclear fusion “lights” up the sun o Gas/vapor blown away from the sun, cools and re- condenses as dust o Planets grow from that dust  Condensation of Planetesimals from dust and gas o Abundant elements bond w/ themselves (ex: H2) very few are unreactive (noble gases) o Elements will bond, compounds are formed if close enough  Many elements give up e-„s willingly to others (metals like Al, Fe, Si give to C, N, O for ex)  When they get close enough, e- donors bond with e- acceptors o Planetesimals clump due to gravitational pull and bonding o Get bigger and bigger  Progressively less gas and dust  Fewer, but larger planetesimals  Planetesimals merge to form planets (10‟s to 100‟s million yrs) o Impacts play a significant role in the growth  Orbits are erratic as growth occurs but can collide, need to settle into clear orbits around the sun  Transferring energy  Heated the earth, creating magma. An Fe rich fraction of this liquid settled to the Earth‟s center The Earth  Melting drove off any H, He rich primordial atmosphere  By 4.4 Ga (billion yrs) Earth had: o A solid core (Fe core condensed under pressure) o An outer core of liquid metal  Partially molten mantle (siliceous, SiO2 rich magma)  Thin skin of cold rock – the primordial crust at surfave, think of stuff that forms on top of soup, VERY much thinner than now  This surface was too hot for liquid water Each planet and atmosphere is unique and different from the next  They did not all follow the melting thing earth did  Why? They are diff, but some are more similar than others o Earth vs Mars  Different sizes, both siliceous  The terrestrial planets (mars venus earth) o Jupiter and Saturn  Mostly gas (H and He rich primordial atmosphere: these gases were abundant while planets were forming) o Uranus and Neptune  Same compounds as gas giants, but its sooooo co
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