EPSC201 Section 1&2 Review.doc

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McGill University
Earth & Planetary Sciences
EPSC 201
Anthony Williams- Jones

EPSC 201 UNDERSTANDING PLANET EARTH SECTION 1: From the Big Bang Theory to the birth of the planet The Big Bang · All energy was concentrated in an infinitely small volume – estimated13.7 bya · Universe was all energy – no matter, infinitely hot 2 · E = mc → convert energy to matter → universe cools as it expands · The universe is continually expanding Evidence of an expanding universe: Background info: · Doppler effect – you hear a higher frequency when noise making object is moving towards you · In the visible spectrum, blue light has a high frequency, and red light has a low frequency · If the object were coming toward you, there would be a blue shift · If the object were moving away from you, there would be a red shift Hydrogen and Red Shift · The universe is ~75% H · Absorption spectrum of H= wavelengths of light at which H absorbs light · Point spectrometer at star – the absorption spectrum of H shifts → virtually all galaxies are red shifted → everything is moving away from us Hubble and the Age of the Universe v = Hd v = d/t t = 1/H Hubble wanted to estimate the age of the universe. He could figure velocity at which stars are moving away from us by measuring the amount of red shift. To figure out the distance from stars: · Can’t simply plot luminosity as inversely related to distance away – not all stars are the same and they have vari- able brightness · Plotted apparent brightness to period of max brightness to min brightness then extrapolate to get 0 period · Got absolute brightness scale to figure out the distance Then he plotted recession velocity (from red shift) against distance (from brightness scale) → H is slope of line. His estimate was 13.4 x 10 years 9 · Pretty good estimate, although modern estimate is 13.7 x 10 years because the universe hasn’t been expanding at a constant rate Expansion of Universe Will the universe continue to expand or will it shrink back? · Problem: we don’t know mass of the universe – because we don’t know much about dark matter which could com- pose a lot of the universe’s mass · As the universe expands, it is fighting gravity · Will gravity eventually dominate as more mass is created as universe expands?? The Big Bang At 10-10s, 10 degrees · When energy is converted to matter you have subatomic particles called quarks (building blocks – up, down, strange, charm, top, bottom) buzzing around · Universe = soup of matter and antimatter, expanding -6 10 At 10 s, 10 degrees · Universe now making protons (up, up, down) and neutrons (up, down, down) · Still antimatter – but matter eventually wins out At 3 min, 10 degrees · Cooling down → particles interact: larger particles being formed · Protons and neutrons collide and combine to form nuclei · Ex – Deuterium (isotope of H) = 1 proton + 1 neutron; Li and He nuclei also formed · No atoms yet – still too hot Nucleosynthesis: > 1 sec, < 5 min after Big Bang · Nuclear reactions give rise to new particles, generating energy · Nuclear fusion occurs · Neutrinos, positrons, gamma rays involved At 300 thousand years, 6000 degrees · Atoms form (electrons orbit around nuclei) · Atoms don’t absorb energy as easily – more organized universe 379 thousand years Last scattering of CMB (Cosmic Microwave Background Radiation) · Energy decoupled from matter · Earlier → energy scattered among subatomic particles (energy bounced around between particles) · Analogy: light is scattered in cloud on a cloudy night → can’t see individual stars · Atoms combine to form molecules, matter starts to separate, radiation no longer scattered CMB and Black Body Radiation · Black body radiation – no atoms are absorbing energy from spectrum; expect before 379 thousand years (no atoms) · Peak shifts to longer wavelengths at lower temps · Measured spectrum = theoretically produced from Big Bang theory · Average temp now: 2.75 K (-270 C) Picture of Universe: · Clusters of warm and cool areas · There are clusters of mass in warmer areas → energy released when they collide · Gravity will be dominating force – masses come together Formation of Stars · As particles come closer together, temperature increases and star factory created At 10 million degrees (critical temp): → Electrons are stripped, nuclei collide (nuclear synthesis) → Cloud of stars – star factories form → Stars pull in other material, tends to spin (conservation of momentum) - form series of spirals, eddy currents → Star factory becomes galaxy (our galaxy - The Milky Way contains 400 billion stars) · Nuclear fusion reactions create the energy that makes stars shine · Our Sun – He is created from collisions of H, core temp is 15 million · Stars with higher temperature can create heavier elements * luminosity and surface temperature of stars show a roughly linear relationship Evolution of Galaxies · As the galactic material starts to spin, disks or spiral arms form in the outer parts and mass concentrates in the centre to form a core · Eddies develop in the outer parts to form stars, the core becomes hotter and more massive due to gravity, core becomes a black hole (so massive that nothing, not even energy, can escape it) · Our galaxy is 90,000 light years across, 3000 light years thick, and rotates on its axis every 250 million years and has a black hole at centre Birth and Death of a Star Birth · Starts as a blob, then develops into a protostar · Begins to burn H at core, pulls in matter due to gravity - force of gravity (compression) > nuclear reaction force (expansion) · Star shrinks to an equilibrium point where the force of gravity equals the force from the nuclear reactions at the core Death · Eventually, the core will run out of fuel (H), so it burns H in the outer parts · This makes it easy to overcome the force of gravity - force of gravity (compression) < nuclear reaction force (expansion) · The star expands, becoming a red giant or supergiant (at end of life) · The core will collapse, increasing the temperature to hundreds of billions degrees → more nuclear reactions form- ing larger elements · So much nuclear energy causes an explosion → Supernova · Core will either become a black hole or neutron star (in case of a initially large star - > 8 times the mass of our sun) Our Sun · Our Sun is a “middle aged star” – formed 4.65 bya and will die in about the same amount of time · Also relatively small · Will eventually expand to Jupiter’s orbit, then gently fizzle out to a white dwarf star · Same will happen to a star < 8 times the Sun’s mass Supernovas viewed · Crab Nebula – 1066 AD · Eta Carinae – 2003 Evolution of the Solar System · The nebula (cloud) condenses into a swirling disk, with a central ball surrounded by rings · The ball at the centre becomes the Sun, dust (solid particles condenses in the rings) · Dust particles collide and stick together forming planetesimals · Earth (and other inner planets) mainly composed of Fe and olivine because they condense at higher temperatures – about 1800 C · Eventually gravity shapes the planet into a sphere (because it is the shape with the smallest surface area to volume ratio) · The outer planets – “gas giants” are composed both materials that condense at high temperatures and materials that condense at low temperatures (gases like NH , CH ,3CO )4 2 · Pluto is not a planet (2006)! Its orbit isn’t really around the Sun. - it is now classified as a dwarf planet – there are others similar to it in the Kviper belt in the outer region of our Solar system Moons · Io – a moon of Jupiter; large and therefore round; surface is continually changing (volcanic eruptions) · Almathea – another moon of Jupiter; smaller and potato shaped, not active and ther
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