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Earth Science and Climate Change Session 2 “The Earth – An Introduction” Bradley Hubbard-Nelson Concord Carlisle Continuing Education Fall, 2014 The earth – such a nice place to be • Rather unique circumstances make the earth not only a habitable planet, but comfortable, bountiful, magnificent… o Distance from the sun, given the sun’s radiated heat, provide a temperature where we can have liquid water o Size of the earth make the gravitation not too strong to support us o Atmosphere has evolved to be a nice mix of gasses (shaped by the biosphere) The Solar System (not to scale) If the planets were drawn at the correct distance from the sun and each other, they would be tiny dots, impossible to see Brief history of the solar system • After the big bang (13 billion years ago), the solar system originated around 4.6 billion years ago in the gravitational collapse of a molecular cloud • The earth and other planets formed along with the sun when the rotating disc of dense, hot gasses coalesced into liquid droplets, and solidified as they continued to cool. Oldest rocks ~ 4.4 billion years old • Inner planets (Mercury through Mars), closer to the sun, formed mostly from elements with relatively high melting points (Iron, Nickel, Aluminum and Silicates), while the outer “gas giant” planets condensed from much more abundant gasses "ʺProtoplanetary-‐‑disk"ʺ by NASA -‐‑ NASA; hKp://origins.jpl.nasa.gov/stars-‐‑planets/ra4.html. Licensed under Public domain via Wikimedia Commons Early history of earth • Earth’s atmosphere caused probably by volcanic outgassing, but contained no oxygen, mainly water (H2O), carbon dioxide (CO2) and nitrogen (N2) • Frequent collisions with numerous proto-planets, allowed the earth and other terrestrial planets to grow to current sizes • Gradual cooling from molten state to form a solid crust, which allowed continents to form and liquid water to exist on the surface • A glancing collision with a protoplanet suspected of forming the moon and tilting the earth’s rotation axis, presumably while the earth was still molten The Earth and its Orbit • Radius Re = 6370 km (3958 mi) = 6.37 x 106 m • Mass Me = 6 x 1024 kg • Distance from sun De = 150M km = 1.5 x 1011 m (93M mi) on average, varies +/- 1.3% (the “eccentricity”) Orbit periods of the planets Kepler (16th century) observed: period T2 ~ D3 2 ! $ 3 4 π 2 &D More accurately: T = # " G * M SUN % Where G = gravity constant, M is the mass of the big object you’re rotating around Planet Distance T (Revolution) Radius T (Rotation) Mercury 58M km 88 days 2440 km 59 days Venus 108M km 224 days 6054 km 243 days Earth 150M km 365.25 days 6370 km 24 hrs Mars 228M km 687 days 3397 km 24.6 hrs Jupiter 778M km 11.9 years 71,492 km 9.8 hrs Pluto* 5913M km 248 years 1137 km 6.4 days Halley** 90-‐‑5200M km 75 years 11 km Comparison with nearby planets • The earth is in what is called the Circumstellar Habitable Zone (“the Goldilocks zone”) Venus – too hot! 462°C due to dense CO2 atmosphere Mars – too cold! -‐‑50°C average due to very thin atmosphere Solar radiation • Surface area Ae = 4π Re2 = 5.09 x 1014 m2 • Sun radiation power: Isun = 3.9 x 1026 W (1 Watt = 1 J/sec) • At earth distance, solar power/area is: ! I sun $ 2 S0 = # = 1370W / m 2& " 4π De % at the top of the atmosphere (absorption ignored) • Changes with time: ! De $ S(t) = S0 * # & " D(t) % 2 • Minimum(June): Smin =1333 W/m2 • Maximum(Dec): Smax =1407 W/m2 • Solar output varies in time << 1% in ~11 yr solar cycle Earth’s Rotation • One rotation per 24 hour day • Velocity at equator V = distance/time = (2π Re)/(24 hr) = 1668 km/hr (~1000 miles/hr) • Rotation plays a role in climate by its effect on the oceanic and atmospheric circulations, through the Coriolis effect. For example: o Gulf stream (surface ocean current) o Overturning circulation (deep ocean current) o Hadley Circulation (tropical air circulation) o Mid-latitude eddy’s (our weather patterns) Latitude and Longitude Spherical polar coordinates: R-‐‑ radial distance from earth center (constant) Θ (theta) -‐‑ latitude angle [-‐‑90° to 90°] Φ (phi) -‐‑ longitude angle [-‐‑180° to 180°] zero arbitrary Degrees subdivided into minutes (x60) and seconds (x3600) Distance between longitude lines gets smaller at high latitude: # 2π *ΔΦ & LΦ = Re * % * cosΘ o ( $ 360 ' Seasons and latitude • Declination angle 23.5° gives us seasonal variability Length of day Zenith angle Season variations from sun’s angle Intensity as function of zenith angle ζ: S(ζ ) = S0 * cos(ζ ) ζ (ignoring absorption by atmospheric gasses) Total incoming (W/m2) Noon “Insolation” (at T.o.A.) 1600 1400 Concord 1200 1000 Miami 800 600 Singapore 400 200 0 1-‐‑Jan 11-‐‑Apr 20-‐‑Jul Date 28-‐‑Oct Earth’s water (the “hydrosphere”) • Earth’s surface mostly covered with water (71%) which scientists think came with asteroids and comets • Ocean typical depth 4km (a very thin covering relative to the earth’s radius 6370km radius (0.06%)) • Oceans moderate earth’s temperature in the short and long time scale Oceans and seas • Fresh water only 2.5% Ice caps and glaciers Saline groundwater 70% locked in ice Fresh groundwater • Water vapor (0.001%) Permafrost Strong climate Lakes Atmosphere influence Swamps Rivers Soil moisture Biological Oceans – basic features • An incompressible fluid – nearly uniform density, depending slightly on salt content and temperature • Large heat capacity – 1000x that of the atmosphere – strong but slow effect on climate • Salty : typically 3.4% concentration by weight • Acidity: pH of 8.1, about 0.1 lower (25% higher acidity) than pre-industrial value from CO2 absorption Tropical paradise Southern Ocean Sea Surface Temperature • Varies dramatically with location and time of year • Temperature units: °C = 5/9 * (°F-32°) = (°K - 273.15) H20 based scale: 0°C = freezing, 100°C = boiling °C °F 0 32 5 41 10 50 15 59 20 68 25 77 30 86 35 97 40 106 0°C 10°C 20°C 30°C 3 layers, by temperature • Mixed layer at sea surface, 50-100m depth, winddriven wave mixing, sizable currents (up to 2m/sec) • Thermocline, 500-600m thick, large T gradient • Abyss, deep layer, cold (0-2°C), very slow currents (<1m/hr), less well understood and measured Ocean currents • • Wind driven currents, constrained by land masses Persistent “gyres” - CW in Northern hemisphere, CCW in southern, separated by equatorial current Ocean currents play critical role in climate by transporting heat Count Rumford (1800): “if the water of the ocean … descends to the boKom of the sea, cannot be warmed where it descends,…, it will immediately begin to spread on the boKom of the sea, and to flow towards the equator, and this must necessarily produce a current at the surface in an opposite direction.” First gulf stream map (Ben Franklin) Ocean current dynamics • Fascinating subject of research, involving complex geophysical fluid dynamics (GFD) • Surface currents have “permanent” features and also chaotic “weather” patterns which last for weeks or months NASA/MIT Ocean Current Simulation Geomorphology – formation and structure of the earth Layer Thickness State -‐‑ Ocean floor 7-‐‑10 km Solid Si/Mg/Fe -‐‑ Continental 20-‐‑70 km Solid Si/Al/Fe Mantle 2900 km Viscous Outer core 2200 km Liquid Fe/Ni Inner core 1200 km Solid Ni Temp Lithosphere (crust): • Magnetic field from fluid flow in the outer core (“dynamo”), changes with time and may have had climate impact; • Core heat ~1/2 from radioactive decay, rest is primordial heat • Heat loss through lithosphere ~ factor of 10,000 less than incident solar 800-‐‑4000°K 6000°K Lithosphere movement • Thin Lithosphere (‘rocky crust’) divided into continental plates, floating on earths semi-liquid mantle • Important geologic processes occur where plates come together or separate • Earthquakes, volcanos are the external phenomena Continental Drift – Plate Tectonics • Continental plates move at speeds of 10 to 40mm/yr • Time scale for large movement (1000km) of order: Time = Distance/speed = 106m/10x10-3m/yr = 100 M yr • • Thought to have been one continent during Cretaceous period (early dinosaur age) Continental arrangement very different than today – most land in southern hemisphere Ocean & land masses Note distortion on rectangular projection (Continental US really ~4x bigger than Greenland Arctic: frozen à Temperate: wet à Sub-‐‑tropics: dry à Tropics: very wet à Sub-‐‑tropics: dry à Southern Ocean à Antartic: frozen à Distribution of land not uniform 80% 70% Land fraction 60% 50% 40% Antartica 90% Concord 100% North Pole Most of the land in northern hemisphere Continental arrangement plays dominant role in climate, particularly regionally Southern Ocean • • Land fraction Area Weighted 30% 20% 10% 0% -‐‑90 South -‐‑60 -‐‑30 0 30 Latitude 60 90 North The Earth’s Atmosphere • A thin gaseous skin with multiple layers • A compressible fluid - Pressure, density fall exponentially with height - 80% of atmosphere inside 10km Atmosphere at moon-‐‑rise from the International Space Station Atmosphere structure Four layers, differentiated by the temperature gradient: Pressure units: 1 atm (sea level) = 1000 hectopascals = 1000 milliBar The troposphere and (to a lesser extent) the stratosphere are important for climate Tropospheric gas mixture • What are these? • How did it get this way? Volume fraction N2 -‐‑ Nitrogen (diatomic) O2 -‐‑ Oxygen (diatomic) Ar -‐‑ Argon (Noble gas) H2O CO2 other Atmospheric constituents Name Activity % Where from? Absorption Respiration of living vegetation, plankton Absorbs visible N2 Nitrogen Mostly inert 78% O2 Oxygen Active 21% Ar Argon Totally inert 0.9% Radioactive decay of 40K (Potassium) No absorption Somewhat active 0.2-‐‑ Evaporation, plant 0.5% respiration Absorbs IR and visible H2OWater vapor CO2 Carbon Somewhat dioxide active 0.04% Volcanos and humans (fossil Absorbs 400ppm fuel burning, agriculture, etc) infrared CH4 Methane Active 1.7 ppm Organic decay Absorbs infrared Highly active 500 ppb Exhaust, photoproduced in stratosphere Absorbs IR and UV Somewhat active 310 ppb Agriculture Absorbs infrared Inert <1 ppb Absorbs infrared O3 Ozone N2O Nitrous oxide Freons Refrigerant, industrial processes History of the Atmosphere • Atmospheric gasses have changed dramatically since the formation of the earth • Strongly influenced by life forms and gradual oxidation of the lithosphere • Early sun was 30% weaker (strong greenhouse effect) General features of changing gas mixture with time (Source unknown) Appearance of Oxygen Stages 0.5 1 3 2 4 5 Atmosphere P O 2 (atm) 0.4 0.3 0.2 0.1 0 3.8 ? 3 2 1 Ga 0 Stages: 1: Practically no O2 in atmosphere 2: O2 produced, but absorbed in oceans & seabed rock. 3: O2 starts to gas out of oceans, but is absorbed by land surfaces. 4 & 5: O2 sinks filled and the gas accumulates. Modern stromatolites (Shark Bay, Australia): rock structures made of cyanobacteria, which contribute O2 to the atmosphere • Heinrich D. Holland - Oxygenation-atm.svg. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons Carbon dioxide (CO2) • A trace gas (0.04% by volume), oversized climate effect • The “Keeling curve” measured since 1958 started by Charles Keeling (Scripps institute of Oceanography) • Seasonal variation with Northern hemisphere respiration Currently, more than ¼ of CO2 molecules in the atmosphere was put up there by humans (and will stay for centuries) Ozone – stratospheric gas, tropospheric pollutant • Ozone (O3) created in stratosphere, shields us from most harmful UV rays • O3 in troposphere is a greenhouse gas (GHG) • Stratospheric O3 has been depleted by long lived synthetic chemicals • Example of coordinated societal action to solve a similar atmospheric crisis Water vapor • The most plentiful greenhouse gas (~0.25% typical) • Continuously changing with time scale in days • Concentration a strong function of temperature, latitude and altitude Equator Concord Arctic Parts per thousand by weight Water vapor and clouds • Water exists on earth in all 3 phases (solid, liquid and gas), so affects climate in numerous ways • As vapor, is the most prevalent GHG (warming) • Frozen in icecaps and glaciers, it reflects light due to its low albedo value (cooling) • Cooling as air rises, forms clouds of liquid droplets, blocking sunlight (cooling) and extracting and releasing energy from the atmosphere and land General circulation, effect on regional climate • Rising air, driven by moisture, cools and expands outward, causing wet and dry regions in tropics and subtropics Atmospheric circulation • Like the ocean circulation, wind patterns move heat and affect the climate dramatically • Winds driven by pressure gradients (change of pressure with position) which themselves are due to temperature gradients • Earth’s rotation causes air to flow around pressure H L extremes, so-called “geostrophic flow” – not from high pressure to low Paleozoic era “Carboniferous” Mesozoic era “Dinosaur age” Proterozoic Eon Cenozoic era present -‐‑ Human predecessors -‐‑ Great apes 60 My -‐‑ Primtes extinction event 150 My -‐‑ Birds 130 My -‐‑ Flowering plants Archean Eon 200 My -‐‑ Mammals extinction event 300 My -‐‑ Reptiles -‐‑ Amphibians 400 My -‐‑ Insects, seeds -‐‑ Land plants 500 My -‐‑ Fish -‐‑ Simple 600 My animals Eucaryotes (complex cells) Cyanobacteria, photosynthesis Prokaryotes (simple cells) -‐‑ Earth formed Appearance of different life forms in geologic record 600 My present -‐‑ Simple animals 1.0 By -‐‑ Multicellular life 2.0 By 3.5 By 4.6 By Timeline of life on earth • • • • • • • • • • • • Major events Earth forms 4.6 billion years ago Life starts (?) 3.8 billion years ago Age of Bacteria: Archaean era Oxygen atmosphere: 2 B years ago. Eukaryotes develop. Proterozoic era 650 M years ago. First multicellular life, forms unknown today Cambrian explosion: wide variety of life forms appear 550 million years ago Paleozoic era: 550 – 250M years ago. Marine invertebrates, fishes, amphibians, invasion of land. Coal formation. Permian mass extinction: 250 million years ago. 95% of all life dies; end of Paleozoic Mesozoic: 250-66 million years ago. Age of dinosaurs (reptiles). Mammals, birds, and flowering plants Cretaceous mass extinction: asteroid hits the Earth, killing much of life, including the dinosaurs. Cenozoic era: 65 million years ago - present. Mammals dominant Cenozoic Era • From 65 million years ago, continues to present. • Mammals become the dominant life form on land. An “adaptive radiation” that took advantage of the sudden loss of dinosaurs. • Another large group evolves: the grasses. • Adaptive radiation of birds and flowering plants. • Geologically, continents that had been separated started to collide: Africa with Europe, North America with South America, India with Asia Modern period (since dinosaurs) Climate from Cenozoic era through modern day: CH4 • Glacial/interglacial cycles, mostly glacial • Holocene may be a typical interglacial cycle • Source: National Climatic Data Center (NOAA) Holocene Last million years (ice core data) 600ppb 300ppb CO2 300ppm NA Ice thicknes s 200ppm 50M 0M -‐‑10C 1000 900 800 700 600 500 400 300 200 100 Time Before Present (Thousands of Years) 0 Global temp 0C