Climate ChangeThroughout the Solar SystemLecture 11: Earth as a PlanetAstro 202Prof. Jim Bell ([email protected])Spring 2008But first...PDFs for Lectures 7, 8, and 11 are postedPaper 3 is due at beginning of class ThursdayPaper 4 is now posted onlinePaper 4 is due at beginning of class on Mar. 13No extensions over Spring Break!Lectures 9 and 10 will be posted online soonInterior Atmosphere Crust Lithosphere Plate Tectonics LifeEarth as a Planet!Overview of Earth's basic properties!Earth's Surface and Interior–Surface Geologic Processes–Composition and Structure–Evolution of the Surface!Earth’s Atmosphere and Climate–Earth's atmosphere–Weather and climate–The greenhouse effect–Cosmic influences on the biosphere5Basic Properties of the Earth Average Distance from Sun: 150 million km = 1 A.U.Period of Rotation around Sun: 365.25 days = 1 yearPeriod of Spin: 23 hours, 56 minutes, 4 sec = 1 dayMass = 5.98x1024 kg = 1 MERadius = 6378 km = 1 REDensity = 5.5 g/cm3Escape Velocity = 11.2 km/sec (~ 25,000 mph) = vEAtmospheric Pressure = 105 N/m2 = 1 bar = PEMost of surface covered by liquid waterAtmosphere mostly N2, but with abundant free OSurface geologically active and young!6Other Properties!Earth has one large Moon !Earth has a strong Magnetic Field7Earth's Surface Topography8Earth's Surface Topography http://homes.jcu.edu.au/~glpww/EA1002/Geomorphology/Oceanography.htmlEarth'stopographyis“bimodal”• Deepest: -11 km• Highest: +8.8 km• 71% under water9Composition of the Earth’s Crust!Earth's crust is only ~ 0.4% of Earth's mass!But it is what we directly sample!!Earth's crust consists of three rock types:– Igneous: Rocks melted then cooled– Metamorphic: Rocks changed by heat+pressure– Sedimentary: Fragments created by erosion10Sedimentary Rock• Layers, beds, dunes, etc. • Formed by wind, water, iceMarsEarth11Metamorphic Rock• High pressure• High temperature• Compression and folding of previous igneous or sedimentary rocks12Igneous Rock• Example: volcanic rock from Hawaii• Dozens of active volcanoes on Earth today!• Not all igneous rock is erupted onto the surface13Volcanoes of the World (USGS)14Earth's Surface is Divided into Plates!15The Plates Move!Lots of Action at Plate Boundaries...16The fact that the plates move was highly controversial when first proposed (Wegener, 1915)"Anecdotal" evidence:S. America & Africa fit like a jigsaw puzzleBetter evidence: Magnetic "stripes" on the seafloorOther evidence:• Similar fossils across continents• Similar rocks across continents• Earthquakes at plate boundaries• Very young age of seafloor17Abundant geologic evidence of tectonic forces at work on our home world18 And these forceshave been actingfor long periodsof time!19Have there been asteroid impacts on the Earth?• Several hundred impact craters identified on Earth• Most highly degraded by wind, water, ice, tectonics• Geologically "rare"Yes!http://www.unb.ca/passc/ImpactDatabase/20Earth:What's Inside?!! implies rock+metal!"Onion Skin" layering– From differentiation!Crust, Mantle, Core– Crust is thin (5-10 km) under oceans – Crust is thick (20-70 km) under continents– Mantle is hot but solid --> convection– Core is liquid (outer) or metallic (inner)21How do we know what's inside? We can directly measurethe behavior of seismicwaves that travel throughthe Earth's interiorEarth's Atmosphere Composition of the Earth’s AtmosphereGasSymbol Percent PPMPermanentNitrogenN278.08OxygenO220.95ArgonAr 0.93NeonNe 0.0018 18HeliumHe 0.0005 5HydrogenH20.00006 0.6XenonXe 0.000009 0.09VariableWater VaporH20 0 to 4Carbon DioxideCO2.0364 364MethaneCH4.00018 1.8Nitrous OxideN2O .000031 0.31Ozone (Troposphere)O3.000004 0.04Ozone (Stratosphere)O3.0012 12Particulates.000001 0.01Chloroflourocarbons.00000001 0.0001• Highly oxidizing atmosphere ("Non-Equilibrium")• Surface pressure: 1 bar (~ 1 kg/cm2)• 1 bar = 10 m of water• Oceans equivalent to 300 bars!Origin of the Atmosphere!Three main possibilities:– (1) Primordial: Formed along with the rest of the Earth ~4.6 billion years ago– (2) Internal: Gases released by volcanism over the history of the Earth– (3) Extraterrestrial: Volatiles delivered from impacts of icy comets and asteroidsVolatiles: materials that evaporate at relatively low temperaturesAtmosphericGainsAtmosphericLosses25"Weather" vs. "Climate"!Day-to-day, quasi-random fluctuations in atmospheric circulation and precipitation are called weather!Patterns of weather observed over decades to centuries are the climate!Weather changes quickly; climate slowly!Climate changes have occurred throughout Earth's history (how do we know this?)Evidence for Past Climate Change • Geologic evidence for massive glaciations: glacially-carved landforms, transported boulders, till, moraines, etc.• Fossil evidence: periodic fluctuations in warm vs. cold water organisms• Variations in Oxygen isotopes: 16O evaporates easier than 18O and thus is more enhanced in snow & ice sheets. So 18O enhanced in seashells in ice ages• Greenland and Antarctic ice cores show variations in temperature, dust• Last ice age was ~20,000 years ago• Others at 150,000; 250,000; 350,000...• Caused by changes in Earth's orbital parameters? (theory...)http://en.wikipedia.org/wiki/Image:Co2-temperature-plot.svgWill the Climate Change in the Future?Naturally by fluctuations in Earth's orbital parameters?ORWith a little (or more) help from humans?(or both?)Yes!28An example of some "help"...The Antarctic Ozone Hole19791998High O3Low O3Why is Ozone important?How did this happen?Ozone Layer• Creation of ozone blocks high energy UV radiation from getting to Earth's surface• Makes life possible!30The Ozone Layer• Destruction of ozone allows more UV to get to the surface:• Health risks!Cl and other O3destroying phases last hundreds of years in the atmosphere!Another example...Atmospheric carbon dioxidemeasured from Mauna Loa, HIWhy is CO2 important?http://en.wikipedia.org/wiki/Image:CO2-Mauna-Loa.pngprevious natural “record”The Greenhouse Effect!Some of the infrared (heat) radiation that would normally escape to space is absorbed by certain gases in the Earth's atmosphere!This is the greenhouse effect, responsible for warming the Earth by more than 30°C above its equilibrium temperature!Carbon dioxide