Great Ideas in Science: Lecture 9 – Earth as a Planet Professor Robert Hazen UNIV 301 Great Idea: Earth, one of the planets that orbits the Sun, formed 4.5 billion years ago from a great cloud of dust and gas.

Today: Key Ideas About Earth 1.Earth, one of the planets that orbits the Sun, formed 4.5 billion years ago from a great cloud of dust and gas. 2. The surface of our planet changes constantly; no feature is permanent. 3. The entire Earth is still changing, due to the slow convection of soft, hot rocks deep within the planet. 4. Earth materials move in cycles; a change in one cycle affects others.

Clues to the Origin of the Solar System Solar System = Objects gravitationally bound to the Sun

Clue #1: Planetary Orbits Features of solar system –All planets orbit in the same direction –All planets orbit in the same plane –Most planets rotate in the direction of orbit

Clue #2: Distribution of Mass Almost all mass is in the Sun (99.9%) Two types of planets –Terrestrial planets –Jovian planets Other objects –Moons, asteroids, comets

The Nebular Hypothesis

Terrestrial (Inner) Planets Mercury, Venus, Earth, Mars –Rocky and relatively small –Mercury and Venus too hot for life –Mars may have had life long ago

Terrestrial (Inner) Planets Mars Exploration –Multiple missions –Found evidence of water

Jovian (Outer) Planets Jupiter, Saturn, Uranus, Neptune

Jovian (Outer) Planets Jupiter, Saturn, Uranus, Neptune –Layered structure –No solid surface

Pluto and the Plutoids –Only 0.3% of Earth’s mass –Three moons –Captured comet or asteroid? –Is it a planet?

Asteroids, Comets, and Meteors Asteroids Small rocky bodies Orbit sun Asteroid belt Comets Dirty snowballs Highly elongated orbits Stardust and Deep Impact missions Meteors and Meteorites Meteor showers Original solar system material

The Formation of Earth The Great Bombardment

Differentiation Heat produced from collisions Dense material sank to center Lighter material rose to surface Layered structure –Core –Mantle –Crust

The Formation of the Moon “Big Splash” Large object impacted Earth Parts of mantle blown into orbit Moon formed from this material

The Formation of the Moon “Big Splash”

The Evolution of Earth’s Atmosphere 1.Volcanoes released N 2, CO 2, H 2, & H 2 O 2.Large impacts blew off most atmosphere 3.Hydrogen lost by gravitational escape 4.Living organisms introduced oxygen

Volcanoes and Earthquakes: Evidence of Earth’s Inner Forces Volcanoes: Magma breaks through surface

Volcanoes and Earthquakes: Evidence of Earth’s Inner Forces Earthquakes –Rocks breaks along fault –Energy transmitted as wave –Tsunamis

The Case of the Disappearing Mountains Young Old

Deep Time James Hutton at Jedburgh Scotland ca.1790

Deep Time 1.Sediments 2.Burial 3.Uplift 4.Sediments

Plate Tectonics Great Idea: Earth is constantly changing, due to the slow convection of soft, hot rocks deep within the planet.

Plate tectonics – 6 lines of evidence 1.Physiology: Similar shapes of continents

Plate tectonics – 6 lines of evidence 1.Physiology: Shape of continents 2.Seismology: Earth’s inner structure

Plate tectonics – 6 lines of evidence 1.Physiology: Shape of continents 2.Seismology: Earth’s inner structure 3.Geology: Distribution of rocks and fossils

Plate tectonics – 6 lines of evidence 1.Physiology: Shape of continents 2.Seismology: Earth’s inner structure 3.Geology: Distribution of rocks and fossils 4.Oceanography: Sea floor topography Bruce Heezen and Marie Tharp

Plate tectonics – 6 lines of evidence 1.Physiology: Shape of continents 2.Seismology: Earth’s inner structure 3.Geology: Distribution of rocks and fossils 4.Oceanography: Sea floor topography 5.Volcanology: Ages of Atlantic volcanoes <5

Plate tectonics – 6 lines of evidence 1.Physiology: Shape of continents 2.Seismology: Earth’s inner structure 3.Geology: Distribution of rocks and fossils 4.Oceanography: Sea floor topography 5.Volcanology: Ages of Atlantic volcanoes 6.Paleomagnetismof sea floor rocks

New Support for Plate Tectonics Measurements of the distance between continents North America and Europe are separating at ~5 cm per year

Earth’s Tectonic Plates

Plate Boundaries Three Main Boundary Types – Divergent – Convergent – Transform

Divergent Boundaries

Convergent Plate Boundaries Three Types: 1. Ocean-ocean

Convergent Plate Boundaries Three Types: 1. Ocean-ocean 2. Continent-continent

Convergent Plate Boundaries Three Types: 1. Ocean-ocean 2. Continent-continent 3. Ocean-continent

Transform Plate Boundary

Another Look at Volcanoes and Earthquakes Volcanoes Occur: 1. At Divergent Plate Boundaries 2. Close to Convergent Plate Boundaries 3. Above Hotspots

Another Look at Volcanoes and Earthquakes Earthquakes Occur at: 1.Transform Plate Boundaries 2.Convergent boundaries

Earth’s Geochemical Cycles Earth materials move in cycles; a change in one cycle affects the others. 1. Atoms recycle; they’re used over and over. Reservoirs (Aluminum can) Hydrologic cycle Atmospheric cycle Rock cycle 2. Energy flows through the system.

Geochemical Cycles Account for all the repositories of that substance. Document processes by which the substance moves from repository to another. Gold

ROCK CYCLE: Igneous Rocks Igneous Rocks –Solidify from hot liquid Types –Extrusive rocks solidify at the surface –Intrusive rocks solidify below surface

ROCK CYCLE: Sedimentary Rocks Rocks deposited layer by layer from weathered particles (sand, silt, etc.) or chemicals (i.e., coral).

ROCK CYCLE: Metamorphic Rocks Rocks formed by pressure and heat Examples –Slate –Schist –Gneiss –Quartzite –Marble

Atmospheric Cycle Air mass: Uniform temperature and moisture Weather: State of the atmosphere Climate: Long-term average of weather

The General Circulation of the Atmosphere Circulation powered by Sun –Air heated and rises –Cools and sinks Prevailing winds –Caused by earth’s rotation

Weather Five variables define state of atmosphere –Temperature –Air pressure –Humidity –Cloudiness –Prevailing winds

Climate Gradual change over long periods Influences on climate –Large bodies of water –Ocean currents –Mountain ranges –Position of tectonic plates –Solar output –Greenhouse gases

The Water (Hydrologic) Cycle The total amount of Earth’s water is constant; the same atoms cycle from one reservoir to another Total volume ~ 1.4 billion km 3 Oceans 97.3% Lakes and Rivers 0.01% Groundwater 0.6% Ice Caps & Glaciers 2.1% Atmosphere 0.001% All life %

How does water move among reservoirs?

Ocean Currents Redistribute heat across planet

Ice Ages As the ice caps and glaciers grow, the sea level drops. Cycle tied to Earth’s tilt and orbit

Two facts about water use A human requires about 2 liters of water per day to survive The average American uses about 6,000 liters of water per day

The Water Table The water table will drop when discharge exceeds recharge (like a bank) In the US we “mine” about 100,000,000 gallons of water every day (more than the recharge) Artificial recharge helps Urbanization and pollution hurt