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Chapter 10 - 2HO3.docx

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McMaster University
Life Sciences
Luc Bernier

2HO3 Chapter 10: Origin of Earth and of Life Chapter 10: Origin of Earth and of Life - The earth was formed 4.6 billion years ago, in a universe which was formed 14 billion years ago Formation of the Solar System: - Formation of the Solar Nebula: o The sun formed from the collapsing cloud of interstellar dust and gas o The clouds are many times the mass of the sun o These clouds have a slight rotation which caused them to spin into a solar nebula - Formation of Planets: o As the solar nebula began to decrease in size a proto-sun formed and smaller fragments formed around it (planets) o The hot inner part of the nebula consisted of rocky planets with inner iron portions  The earth and the other terrestrial planets (Mars, Venus, & Mercury) are all composed of rocks o The outer regions of the nebula consist of H2O, CH4 & NH3  This is why the outer planets are composed of volatile compounds  Volatile compounds are substances that have a low boiling point o Some of the small fragments, called planetesimals, collided together to form larger bodies due to a process called accretion  While the earth was growing via accretion its nickel and iron core started to form - Formation of Jupiter: o Has over 300 times the mass of Earth o Jupiter is so large due to the fact that its core accreted early enough to capture large amounts of hydrogen and helium o Jupiter’s core grew quickly and accreted hydrogen efficiently - Formation of the Moon: o Many theories but the most popular and likely one is that a large impact between earth and a large space object occurred  When the two collided, the impact caused debris from the earth to be scattered  The debris then collided and accreted into a moon  The moon continued to rotate around the earth and eventually moved further away due to angular momentum  When the moon was moving quickly it was able to stay close to the earth  The moon was slowing down therefore the radius at which it rotated continued to get larger 1 2HO3 Chapter 10: Origin of Earth and of Life Formation of the Atmosphere and Ocean: - Even after the formation of the moon the earth was further bombarded by planetesimals - This caused the degassing of the earth, which lead to the release of CO2 gases - The energy released due to the impacts and the degassing lead to the earths surface staying hot, this heat would have caused the water on earth to remain as steam o Since then the earths oceans have periodically condensed and re-evaporated Composition of the Early Atmosphere: - Free oxygen which makes up about 21% of our current atmosphere, was non-existent in the early atmosphere o O2 was not present due to the absence of photosynthesizing plants - The current amount of N2 is the same as the amount that was present in the early atmosphere o N2 is very bad at precipitating into the geochemical cycles o N2 would have been formed nitrogen-rich organic compounds and ammonia (NH3) ice - Much of todays CO2 is found in carbonate rocks such as limestone o CO2 was originally brought to earth via incoming comets  The CO2 would have been immediately degasses upon impact, leading to an increase in the amount of atmospheric CO2 o The exact amount of CO2 present in the early atmosphere is difficult to determine Origin of Life: - The Oparin-Haldane Hypothesis: o Life arose from chemical reactions that were initiated in a strongly reduced early atmosphere and came to completion in the early oceans o Energy sources such as sunlight and lightning caused gases (CH4 & NH3) to react with each other to form organic compounds in a process termed chemical evolution o These organic compounds assumed the characteristics of early life - Miller-Urey Experiment: o Used a flask full of CH4 and NH3 along with water vapour and molecular hydrogen o The flask was then sparked with stimulated lightning o After several minutes of electrification the walls of the flask became coated with brown material o The material included amino acids, important compounds for the formation of proteins  Many of the basic compounds on which life depends can be synthetized by a straightforward process that could have occurred in nature 2 2HO3 Chapter 10: Origin of Earth and of Life - The RNA World: o Some scientists believe that proteins were not the earliest structural elements o Instead they believe that RNA molecules were the first elements on earth o It was discovered that RNA molecules were capable of cleaving themselves into smaller molecules  Therefore it is theoretically possible for RNA molecules to replicate itself without the help of any other molecule  This cannot be done in DNA containing organisms, since the require complex enzymes made of proteins in order to duplicate o Life depends on DNA, RNA and proteins o RNA-based organisms could have been much simpler then todays organisms o RNA not DNA could have been the molecule in which the genetic information was stored  RNA is less stable then DNA but it carries the same inform
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