Geobiology 2006 Introductions Rationale The interactive Earth system: biology in geologic, environmental and climate change throughout Earth history. Since life began it has continually shaped and re- shaped the atmosphere, hydrosphere, cryosphere and the solid earth. ‘Geobiology’ introduces the concept of 'life as a geological agent' and examines the interaction between biology and the earth system during the roughly 3.5 billion years since life first appeared. 12.007 GEOBIOLOGY SPRING 2007 Instructor: Roger Summons Guest Lecturers: Professor Richard Binzel Professor Ed Boyle Dr D’Arcy Meyer-Dombard Lectures: Tues. & Thurs. 11-12:30 Course Description: The interactive Earth system: biology in geologic, environmental and climate change throughout Earth history. Grading: 15% Participation in class discussions 20% Problem Sets/Assignments 20% Final Paper & Oral Presentation 20% Midterm Exam 25% Final Exam Week 1 Lecture 1 • Introduction and requirements • Time Scales; Some introductory Geology; How to Make a Habitable Planet: Big Bang; Origin of The elements; How we date things Lecture 2 • Origin of the Solar System, Earth and Moon, early Earth segregation, atmosphere and hydrosphere; characteristics of the ‘habitable zone’ Week 2 Æ What is Life? Theories about the origin of Life Weeks 1&2 Assignment Essay: What is the Universe made of? 4 pages incl. figures Check recent literature on…….. ‘Ordinary matter’ (~4%); we know mostly H, He What and where is the rest and how was it made? ‘exotic matter’ = dark matter (~23%) and ‘dark energy’ (~73%) OR: Essay: What is meant by the concept of Galactic Habitable Zones 4 pages incl. figures Making a Habitable Planet • The right kind of star and a rocky planet • A benign cosmological environment • Matter, temperature where liquid water stable, energy • And many more…………see WS Broecker, How to Build a Habitable Planet Cosmic Time Scales Oxygen December First trees and atmosphere January 1 12 23 reptiles Origin of the February Universe Origin of 2 13 24 our galaxy March First dinosaurs 3 14 25 April 4 15 26 May 5 16 27 June 6 17 28 July Origin of solar system 7 18 29 August Dinosaurs wiped out, First land plants 8 19 30 mammals take over September First primates 9 20 31 All of human October Life on Earth history Origin of sex Neanderthals November 10 21 Oxygen December atmosphere 11 22 Early homo sapiens last 10 minutes The cosmic calender - the history of the universe compressed to one year. All of recorded history (human civilization) occurs in last 21 seconds! Figure by MIT OCW. Avg. human life span=0.15 s Image removed due to copyright restrictions. See illustration in Des Marais, D. J. "Evolution: When Did Photosynthesis Emerge on Earth?" Science 289 (2000): 1703-1705. Time T(K) E Density What’s Happening? The standard cosmological model of the formation of the universe: Figure removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/bbang.html “The Big Bang” New NASA Speak: The theory of The Big Bang •From: The First Three Minutes, by Steven Weinberg Evidence for the Big Image removed due to copyright restrictions. Bang #1: An Illustration of the raisin bread model of expanding universe. Expanding Universe •The galaxies we see in all directions are moving away from the Earth, as evidenced by their red shifts (Hubble). •The fact that we see all stars moving away from us does not imply that we are the center of the universe! •All stars will see all other stars moving away from them in an expanding universe. •A rising loaf of raisin bread is a good visual model: each raisin will see all other raisins moving away from it as the loaf expands. Evidence for the Big Bang Image removed due to copyright restrictions. #2: The 3K See http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod/bkg3.gif. Cosmic Microwave Background •Uniform background radiation in the microwave region of the spectrum is observed in all directions in the sky. •Has the wavelength dependence of a Blackbody radiator at ~3K. •Considered to be the remnant of the radiation emitted at the time the expanding universe became transparent (to radiation) at ~3000 K. (Above that T matter exists as a plasma (ionized atoms) & is opaque to most radiation.) Science Magazine: Breakthrough of the Year 2003 • Wilkinson Microwave Anisotropy Probe (WMAP) produced data to indicate the abundances and sizes of hot and cold spots in the CMB. • Universe is very strange • Universe not just expanding but CREDIT: GSFC/NASA Image courtesy of NASA. accelerating • Universe is 4% ordinary matter, 23% ‘exotic matter = dark matter’ and 73% dark energy • Age is 13.7± .2 b.y. and expanding • It’s flat Evidence for the Big Bang #3: H-He Abundance Image removed due to copyright restrictions. See http://hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/hyhel.gif. •Hydrogen (73%) and He (25%) account for nearly all the nuclear matter in the universe, with all other elements constituting < 2%. •High % of He argues strongly for the big bang model, since other models gave very low %. •Since no known process significantly changes this H/He ratio, it is taken to be the ratio which existed at the time when the deuteron became stable in the expansion of the universe. Nucleosynthesis Image courtesy of Wikimedia Commons. Nucleosynthesis I: Fusion Reactions in Stars Fusion Ignition T Reaction Process (106 K) Hydrogen Produced in H-->He,Li,Be,B 50-100 Burning early universe Helium Burning He-->C,O 200-300 3He=C, 4He=O Carbon Burning C->O,Ne,Na,Mg 800-1000 Neon, Oxygen Ne,O-->Mg-S 2000 Burning Fe is the end of the Silicon Burning Si-->Fe 3000 line for E-producing fusion reactions... Hydrogen to Iron •Elements above iron in the periodic table cannot be formed in the normal nuclear fusion processes in stars. •Up to iron, fusion yields energy and thus can proceed. •But since the "iron group" is at the peak of the binding energy curve, fusion of elements above iron dramatically absorbs energy. Fe The 'iron group' yield from 8 of isotopes are the nuclear fission most tightly bound. r a 62 V e Ni (most tightly bound) l e c 28 u M 58 n Fe n 6 Elements heavier r i e 26 ) 56 p than iron can yield n Fe o y e 26 energy by nuclear g l r have 8.8 MeV c e u fission. n n per nucleon e ( g yield from e 4 binding energy. l n i c i d nuclear fusion t n r i a B p 2 Average mass of fission fragments 235 is about 118. U 50 100 150 200 Mass Number, A Figure by MIT OCW. Nuclear Binding Energy •Nuclei are made up of protons and neutrons, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. •The difference is a measure of the nuclear binding energy which holds the nucleus together. •This energy is released during fusion. •BE can be calculated from the relationship: BE = Δmc2 •For α particle, Δm= 0.0304 u, yielding BE=28.3 MeV **The mass of nuclei heavier than Fe is greater than the mass of the nuclei merged to form it.** Elements Heavier than Iron •To produce elements heavier than Fe, enormous amounts of energy are needed which is thought to derive solely from the cataclysmic explosions of supernovae. •In the supernova explosion, a large flux of energetic neutrons is produced and nuclei bombarded by these neutrons build up mass one unit at a time (neutron capture) producing heavy nuclei. •The layers containing the heavy elements can then be blown off be the explosion to provide the raw material of heavy elements in distant hydrogen clouds where new stars form. Image courtesy of NASA. Neutron Capture & Radioactive Decay •Neutron capture in supernova explosions produces Image removed due to copyright restrictions. Illustration of Cd undergoing neutron capture until an unstable isotope some unstable is produced, at which point it undergoes radioactive decay into a new nuclei. element; see http://abyss.uoregon.edu/~js/images/neutron_capture.gif •These nuclei radioactively decay until a stable isotope is reached. Cosmic Abundance n o e l c u N of the Elements Fusion r e p y g r Fission •H (73%) & He (25%) account for e n E 98% of all nuclear matter in the Fe universe. Atomic number = Number of protons •Low abundances of Li, Be, B due H 10 to high combustibility in stars. 9 He •High abundance of nuclei w/ mass 8 O 4 C 7 divisible by He: e Ne l a c N s Si 6 Fe C,O,Ne,Mg,Si,S,Ar,Ca g S o l Ar The "cosmic" abundance of the e 5 c Ca Ni elements is derived from •High Fe abundance due to max n a spectroscopic studies of the sun d 4 n u supplemented by chemical analyses of Zn binding energy. b K a 3 chondritic meteorites. e F v i •Even heavy nuclides favored over t 2 Cu a Li l e R 1 B Sc odd due to lower “neutron-capture Sn Pb cross-section” (smaller target = 0 Pt Be -1 Bi higher abundance). Au -2 Th •All nuclei with >209 particles U (209Bi) are radioactive. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Figure by MIT OCW. Basics of Geology Lithosphere & Asthenosphere Mantle and Crust Lithosphere/Asthenosphere Outer 660 km divided into two layers based on mechanical properties Lithosphere Rigid outer layer including crust and upper mantle Averages 100 km thick; thicker under continents Asthenosphere Weak, ductile layer under lithosphere Lower boundary about 660 km (entirely within mantle) The Core Outer Core Earth’s Interior: How do we know its ~2300 km thick structure? Liquid Fe with Ni, S, O, and/or Si Avg density of Earth (5.5 g/cm3) Magnetic field is evidence of flow Denser than crust & mantle Density ~ 11 g/cm3 Inner Core Composition of meteorites ~1200 km thick Seismic wave velocities Solid