Study Materials • Final Review Sheet (and these slides) • The sheet and slides are not comprehensive. These slides will be available online later. • SA-54 Final Preparation Google Doc • 25 practice questions with answers and useful comments, some from 2008 final • Midterm and Homework Solutions (conceptual questions, Answer What Is Asked) • Section handouts and your notes • Midterm Review Session video • Lecture slides/videos • Etc.
Section 3: Microorganisms • 3 major Domains—Bacteria, Archaea and Eukarya • Phylogenetic trees are constructed based on comparing sequences of RNA in the ribosomes of different organisms • eukaryote, prokaryote, and Archaeans - horizontal gene transfers • Traits of life – cellular organization, reproduction, metabolism, growth and development, adaptation through evolution
Life and Evolution • Darwin’s natural selection, diversification (mutations and adaptations), permissible environments • Need resources to evolve and diversify (changes in environment, extinctions) • ALH-84001: meteorite from Mars; was thought to contain evidence of biology/life (proved inconclusive)
Life and Evolution • Proteins, Nucleic Acids, DNA, RNA, Ribosomes, Membranes, Carbohydrates and how they interact with each other • Multicellularity requires: Cohesion, Communication, Genetic program to guide cell differentiation • Active predation requires: sensory systems, Coordinated action of many cells (movement), Nerve ganglia that can coordinate stimuli and responses (a brain!) • Only oxygen provides enough energy to fuel active multicellular heterotrophs
Section 4: Rocks and Fossils • 3 rock types – igneous, sedimentary, and metamorphic • Had parts most commonly preserved, some impressions, soft part preservation is rare (Burgess shale) • Can use fossils to date rocks, can use rocks to date fossils • Sedimentary rocks as old as 3.8Ga and contain microfossils, molecular fossils (mainly lipids), stromatolites, and C and S isotopic signatures
Cretaceous-Tertiary (K-T) impact extinction • Permian-Triassic extinction • Extinction causes – volcanoes, impacts, snowball Earth
Section 5: Mars Missions • Missions need • radiation shielding • redundant equipment • communication • minimum weight/fuel/ size for objectives • choose objectives and landing site to best suit mission • Drawbacks • very expensive • don’t always work • take time
Mars • Smaller and less massive, cooled faster than Earth and Venus, differentiated interior • Surface - no plate tectonics, evidence for strong basaltic volcanism in the past • Atmosphere - thin, mainly of CO2 (95%), N2 (2.5%), Ar (1.5%) • Water - water ice in the polar caps, old drainage channels, floods; terrains and impact craters indicating frozen sub-surface water
Habitability • Habitable Zone: range of distances from a star where the temperature on some of the surface of a rocky planet allows water to be liquid • Phase diagrams – triple point: the temperature and pressure at which the liquid, solid and gaseous phases are all stable
Questions • Which of the following is not thought to be a critical aspect of the emergence of life: • Liquid water • Oxygenated atmosphere • A surface or interface • A stable environment • What is the medium of life that renders the Earth a "Habitable Zone"? What properties of this particular medium allow for the emergence of life?
Questions • What are Europa and Enceladus? What are their most notable features? What is the location of Europa with respect to the Habitable Zone in our Solar System? Explain the role tides play on Europa.
Life Outside the Habitable Zone • Europa – water ocean under a solid ice crust; tidal heating • Enceladus – geysers: hydrothermal circulation close to the ice crust surface; pure water observed in eruptions; tidal heating • Titan – largest satellite of Saturn, thick atmosphere of N2 (>90%) and methane (CH4), evidence for CH4 rain, complex organic chemistry on surface
Properties of Light • Visible light - electromagnetic energy (radiation) to which our eyes are sensitive • Energy - depends on the wavelength – smaller wavelength = higher energy • Spectrum - the amount of light of any given wavelength emitted or reflected by an object; • Thermal spectrum - simple spectrum that depends only on the object’s temperature • Spectral lines - absorption or emission at particular wavelength
Questions • Define absorption and emission. • A prominent spectral line of the sodium atom has a laboratory wavelength of λrest= 589.0 nm. We observe the spectrum of a distant star and measure the same sodium absorption line to be at l = 589.12 nm. Calculate the star’s speed and determine whether the star is moving away or toward us. • What are redshift and blueshift? What can it tell us?
How to Answer Quantitative Questions • Deterine what facts you know and what fact(s) you want to know. • Find an equation that includes the fact(s) you want to know. • Make sure this equation is applicable to your problem. • Do you know (given in problem or a universal constant) everything else in this equation? • If yes, solve for that variable (algebraically is best) and then substitute in what you know KEEPING THE CORRECT AND CONSISTENT UNITS • If not, then determine what (intermediate) facts you want to know. Repeat this process. • Check whether your answer seems reasonable. • Write out brief phrases and connecting thoughts that you had while folllowing the above pattern in words to show your work. Include a meaninful and descriptive conclusion.
Remote sensing – observing the spectra and spectral lines of distant stars and planets to determine temperature, abundances of gases, etc. • Telescopes • Main types: refractors (with a lens), reflectors (with a mirror) • Main functions: collecting more light (depends on the area of the lens, angular) resolution (proportional to the diameter of the lens and inversely proportional to the wavelength observed)
Section 6: Meteorites and Asteroids • Meteorites 4.55Ga • Types - Stony, Carbonaceous Chondrites, Pallasites and stony-Iron, Iron • asteroid belt caused by orbital resonance with Jupiter • Panspermia – life transported from one world to another • Impact velocities: KE=½mv2; v~11km/s
Extrasolar Planets • Extrasolar planet detection by Doppler (minimum mass), Transit (size), and Astrometric method (using Newton’s laws –orbital motion due to unseen planet), Direct Imaging (taking a picture), Microlensing, etc. • 450+ such planets known, with ~70 transiting; wide variety of orbits, mostly large planets (easier to see), but Kepler is working its way down to Super-Earths: the more habitable type of planet
Habitable Extrasolar Planets • Super-Earths: two basic families small atmospheres and solid surfaces (water & dry), and mini-Neptunes; ~20 so far • Global geochemical cycles: the carbon dioxide cycle keeps the climate stable on Earth (long term and short term) • Edge on (i=90o) vradial = vorbital can calculate true mass and from transit get radii → densities, etc.
Extrasolar Planet Formulas Semi-major axis: Mass: vplanet=2πa/P and vstar=vradial Radius: Density: Density = M/V = M (4/3)πr3
Understanding Radial Velocity and Transit Graphs RV: Go to website http://library.thinkquest.org/C003763/flash/extrasolar1.htm Transit: http://www.youtube.com/watch?v=a4M4Es3aQ7M Just a couple examples of many many such animations.
Question: what is orbital velocity of the planet? Assume the planet is 1/1000 times as massive as the star. Is the velocity consistent with the duration of the transit?
The Search for Life • Drake equation – estimate the number of civilizations in our galaxy with interstellar communication: N = R*×fp×ne×fl×fi×fc×L • Radio SETI and Optical SETI • Atmospheric biomarkers: pairs of non-equilibrium gases in the atmosphere (O2 and CH4), unusual abundances (O3 indicating lots of free oxygen O2)
Answers to Questions Answers to Questions provided in these slides are in the online Google Doc